# Homemade air filters - Good indoor air quality, cheap



## Poindexter (Nov 1, 2021)

This is pre-pub.  I have a lot of documentation to do after I collect a bale of data.  I wasn't expecting to post here for another 6-8 weeks, but check this out.





This is in my living room, about 10 feet from my wood stove that has been running 24/7 for days.  I also have a geriatric long haired cat in the house, and some 12 year old carpet that was on the block to be replaced "next month" in December 2019.

This is the second of my two particle counters that came in today.  My first particle counter, a Dylos 1100PRO, came in Friday and the numbers I was getting kinda made me wonder if the Dylos didn't get a bump on the noggin knocking it out of calibration.  I just couldn't quite believe the filter system I built is working this good, but it seems to be working that good.

So how did I do it?  Meet the Poindexter box:





Straight up WYSIWYG.  20 inch box fan on low, wafting cool air from the bedroom floors down the hall towards the stove room.  Top and bottom panels are cardboard from the box the fan came in.  The other three sides are 20x20x1 inch MERV 13 furnace filters.  MERV is an ASHRAE (hvac industry) standard.  If you are shopping at the team orange homestore look for filters at level 10.  If you are shopping 3M filters you want either 1900 or 2200.  Assembly, all of it, about half a roll of duct tape.  Tools required, something sharp.  I used a drywall knife and a pair of scissors.  

Assembly instructions: Gather materials.  Cut the two largest possible panels from the box the fan came in.  Assemble with duct tape, trim cardboard to fit as you go.  

I did use 3M 2200 for mine.  As a clinican at the bedside for a quarter century now I think MERV 13 is a very reasonable household filtration level for particles.  If MERV 13 isn't enough, your kid is still sick or etcetera, then look at HEPA and money.  Baseline healthy people in a  baseline healthy house, my opinion, do not require household wide HEPA level filtration.

I have been collaborating, loosely, with a couple guys on a different website.  Alan and David.  One of them is a cardiothoracic anesthesiologist with a professional interest in whole life air quality.  The other is an MSEE who got interested in airflow dynamics as a hobby.  No idea if either will register here.  Also I must give credit to Comparetto of "Comparetto cube" fame, and Corsi and Rosenthal of "Corsi-Rosenthal box" fame.  The Poindexter permutation or Poindexter box is clearly an evolution.  I don't give a hoot if the Poindexter Box is patentable or something that could be monetized.  I want you and your kids breathing the cleanest air you can get so there will be somebody healthy to take care of me when I am old and feeble.  Older and Feebler.

I gave @begreen a heads up a bit ago.  He said this research is going to end up in the green room.  I asked him to leave it in this section for at least a few days so you guys could see it first.  @BKVP , this should be the first you have heard of this unless begreen spilled.  My research is not supported by any commercial entity and I will publish my findings no matter what they are.

For now I am not prepared to exhaustively defend this thing I made, but now I have something to do this winter I can win at doing.  

I do recognize MERV 13 filters don't do anything about VOCs.  I have a plan for that, hopefuly something to say by Christmas.


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## ABMax24 (Nov 1, 2021)

I like the idea, pretty practical and affordable for almost everyone.

Step one for me is air quality monitoring, where did you get that meter from? I'd like to get one for our house.

Edit: Found it on Amazon, will have it Friday.


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## Poindexter (Nov 2, 2021)

ABMax24 said:


> I like the idea, pretty practical and affordable for almost everyone.
> 
> Step one for me is air quality monitoring, where did you get that meter from? I'd like to get one for our house.
> 
> Edit: Found it on Amazon, will have it Friday.



Yup.  My goal wasn't to see how good I can get my air quality.  My goal starting out was how good of air quality can anybody have.

I did put the cart before the horse.  I do not know "how bad" my house air quality was when I started running the filter.  I was running a Corsi-Rosenthal filter in my wood shop in the garage.  One night watching TV upstairs with the wife I went down to the shop to get a beer out of the downstairs fridge, went back upstairs, put my beer down, went back downstairs, brought the C-R upstairs and started running it.

The Corsi-Rosenthal and Comparetto models (configurations?) both break the convective loop I used to have with the box fan on the floor, therefore horizontal output,  et viola.

There is consistent data out there that the $60 particle counter as pictured above runs pretty well neck and neck with the more expensive Dylos.  I will be building my own data set to compare the two with somewhat more robust data sets than I am accustomed to seeing online.  The pictured AQ meter is available on Amazon, and also from a company named "banggood" that will send you many many emails I am told.  I ordered mine from Amazon because I get enough email already.  Also be aware the more expensive Dylos counts particles per cubic foot, there is some assumptions and some math to get to micrograms per cubic meter from the raw Dylos data.

A brief word about VOCs.  There are four methods to measure VOC in an air volume.  Gold standard is to get an air flask in the mail, follow the directions, mail the specimen back to the lab and they hook your sample up to a gas chromatograph machine.  About $200 for a total VOC count, about $400 if you want the lab to print out every little thing to four decimal places.  Among reputable field devices the Flame Ionization Detector (FID) and Photo Ionization Detector (PID) sensor types retail in the $3-10k range but can sometimes be rented, with a hefty deposit.  

Finally, the Metal Oxide Semiconductor (MOS).  You may have heard of MOS-FETs, a metal oxide semiconductor field effect transistor.  A MOSFET is a thing that acts like a transistor but uses the electrical fields generated by the metal oxides instead of physical PNP or NPN  junctions in the dope inside the device.  You can get a MOS sensor to hook up to an Arduino or Pi for about $20,and they appear in full featured "air quality monitors" up to +/- retail $500.  I am not a fan of this sensor for VOC  detection for a number of reasons beyond the intended scope of this thread.

I look forward to finding out where @ABMax24 particulate air quality reads before he builds a filter.


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## kennyp2339 (Nov 2, 2021)

Your side projects always amaze me, solar kilns, anti-smoke re-loads on the stove, to clean in-door air, way cool.


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## EbS-P (Nov 2, 2021)

I’m going to borrow my dads air quality monitor that does pm 2.5 and voc and formaldehyde ect.  and get a weeks worth of data before I start burning.  I think that’s an important number.  I usually run two air purifiers  with a poodle, 4 kids and 100% hard wood floors the dirt is always stirred up and in the summer I need to clean my ac filter very frequently like every two weeks.  All the articles about wood stoves and indoor air quality I would like a personal data point.


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## Poindexter (Nov 2, 2021)

EbS-P said:


> I’m going to borrow my dads air quality monitor that does pm 2.5 and voc and formaldehyde ect.  and get a weeks worth of data before I start burning.  I think that’s an important number.  I usually run two air purifiers  with a poodle, 4 kids and 100% hard wood floors the dirt is always stirred up and in the summer I need to clean my ac filter very frequently like every two weeks.  All the articles about wood stoves and indoor air quality I would like a personal data point.



My wife and I haven't had to dust again since this thing has been running.  I am sure we will have to dust again someday, but I can't tell you what the new interval is yet.


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## peakbagger (Nov 2, 2021)

So next thing to do is incorporate a UVC lamp or two with appropriate shading and interlock to deal with airborne pathogens. I did a lot of work over recent years in various hospitals HVAC systems and I am always running into UVC banks in the supply air ducts. I think they were put in years ago to deal with TB.


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## stoveliker (Nov 2, 2021)

about UVC, just be careful that you measure the ozone concentration. It produces ozone, and too much is not good for your lung (lining) either. Never let that UV light on when air is not flowing (local concentration goes up too much).


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## Poindexter (Nov 2, 2021)

peakbagger said:


> So next thing to do is incorporate a UVC lamp or two with appropriate shading and interlock to deal with airborne pathogens. I did a lot of work over recent years in various hospitals HVAC systems and I am always running into UVC banks in the supply air ducts. I think they were put in years ago to deal with TB.


I am not encouraging healthy adults in healthy homes to take this step at this time.

1. MERV 13 filtration will catch 75% of virus sized particles and 90+% of bacteria and mold sized particles on the first pass.

2. Hospitals are full of sick people, none of the beds are for healthy people to take a nap on their way to the golf course.

3. As @stoveliker already mentioned, ionizing radiation like UV or an "ozone generator" is actually a pollutant on its own.  

For the operating rooms it makes sense to kill every possible living organism in the air ducts to reduce the number of living organisms that get through the skin at the surgical incision.  It also makes sense to not be pumping Legionella bacteria into a room with a sick sleeping elder in it.   But the air coming out of the ducts now has 'some' nonviable organic debris in it, as ionized particles.  So no infectious materials, but ozone as an introduced pollutant and ionized particles as an introduced pollutant.  At the hospital level adding on another filter to deal with the ionized particles and ozone is probably regulated at the federal level.  

At the household level the "cure" may be worse than the disease.  The most common exception would be a home with so much mold in the ductwork (I don't have forced air at all) that a UV light or ozone generator brings the mold counts down far enough to be tolerable, but now the homeowner should be doing something about the ozone and the ionized particles. - and looking at this as a temporary AQ fix while the mold in the duct work is remediated.

I should reiterate that I do NOT advocate sticking a MERV 13 filter in an air handler that is not rated MERV 13.  It will throw your air handler out of balance, just like a super dirty hasn't been changed in 3 years MERV 11 filter might.  I actually joined an hvac forum for this project because I was tired of proving I wasn't a robot everytime I wanted to use the search button.  With an overrated or very dirty filter the most common service call is the condensor coils ice up because of diminished air flow and then the compressor blows up.  Hundreds of dollars to repair.  Or an $80 standalone filter cleaning the air you are actually breathing inside the house might work.


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## ABMax24 (Nov 2, 2021)

Poindexter said:


> Yup.  My goal wasn't to see how good I can get my air quality.  My goal starting out was how good of air quality can anybody have.
> 
> I did put the cart before the horse.  I do not know "how bad" my house air quality was when I started running the filter.  I was running a Corsi-Rosenthal filter in my wood shop in the garage.  One night watching TV upstairs with the wife I went down to the shop to get a beer out of the downstairs fridge, went back upstairs, put my beer down, went back downstairs, brought the C-R upstairs and started running it.
> 
> ...



I'm definitely curious to see what I end up with for air quality. I already run MERV 13 filters in the furnace and do notice an increase in buildup on the filter when the stove is operating. It would have been nice to see a baseline reading before starting the stove, but that will have to wait until spring. I'm also curious to see what the indoor air quality is like when wildfire smoke blows into the area.


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## Poindexter (Nov 2, 2021)

I am posting my first data set now that I have two particle counters telling me the same thing.  I will come up with a more organized way to present data in the future.  All particle counts are expressed in micrograms per cubic meter.

Briefly I did a cold start on my stove last night at 2200 with no visible smoke in the room and trivial readings for air quality in continuous mode.  Once I had the loading door shut I set the Dylos to sample one minute of every hour and store the data.  The $60 thingy from Amazon doesn't record data, just real time display.  So cold start last night at 2200, then hot reload around 0830 this morning.

Sensor was on my chairside table 11 to 12 feet away from the closest vertical corner of the stove on the hearth.  Today I only was able to harvest outdoor PM2.5 data for 0800, 0900, 10, 11 and 1200.

Worst measured air quality (particles only) was at 0900 with indoor AQ 2.56 mcg/m3 of PM2.5 with indoor PM10 at 0.6 mcg/m3, simultaneous outdoor PM2.5 at the NCore sensor seven miles from my house was 13 mcg/m3.

There are many many variables to chase down.  I know perfectly well on hot reloads I am gettng both VOCs and particles coming out the open loading door.  I will eventually set up a tripod near the loading door and hang sensors on it, but my hypothesis is the 'stuff' coming out of the stove on hot loads is a chaotic rather than smooth flow.  Sort of like pouring cream into a cup of coffee, I expect to get perhaps a real high reading here, and then 5 cm away a very low reading.  

I am not interested in peak values for particles and VOCs coming out on hot reloads, I want to know total particles and total VOCs.  I have so far three ways to trial for hot reloads, two of which should produce lowest possible totals, the third should produce max.


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## woodgeek (Nov 3, 2021)

You could get a cheap pressure gauge off eBay and see what kind of pressure the fan is developing. 

Usually, fans don't move a lot of air when there is a back-pressure, and a squirrel-cage blower is more effective.  This translates to higher cfm per watt.


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## peakbagger (Nov 3, 2021)

30 years ago I owned a house in Wisconsin for a short time, the prior owner pulled a fast one and hid a hot air furnace issue and I ended up replacing it. I kept the belt driven squirrel cage blower and it came with me to NH. When I was building canoes and kayaks in my basement I generated lots of dust mostly cedar and it definitely floated around the house. I ended up building a wooden box  out of scrap plywood with filters on either side and the squirrel cage blower inside. It exhausted upwards into the room. I got a case of  filters for cheap at a close out sale of a Home Depot clone (anyone remember Home Quarters?). I had a regular prefilter on top of highest efficiency pleated filters they had (no doubt not up to current standards). It made a big difference when I was doing wood working.  My guess is slowing down the blower and running it continuously would improve air quality if I had an issue. I run a wood boiler with a very aggressive draft so I expect I just do not have the  air quality issues a stove operator would.


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## Poindexter (Nov 3, 2021)

I just saw this, like ten minutes ago, on youtube.

 

Now I got to register on youtube so I can message Troy Gardner and link him here and ask him if I should name this thing a Troy Gardner box.

Somebody figured out a couple years ago my Poindexter username was acutally a cartoon character.  Of the little eggheads, Poindexter is the coolest name, but my favorite character was Egghead Junior:


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## Poindexter (Nov 3, 2021)

woodgeek said:


> You could get a cheap pressure gauge off eBay and see what kind of pressure the fan is developing.
> 
> Usually, fans don't move a lot of air when there is a back-pressure, and a squirrel-cage blower is more effective.  This translates to higher cfm per watt.


I could also put a water tube manometer on it to see when I am getting more pressure drop, I am not too worried about that.  I am using an infrared pyrometer to check the motor temp, it has been stable between 69.5  and 70.5 degrees F so long I don't even check it any more.

One thing I will have to do is turn the fan off for a few hours while tracking temperature in the stove room and the back bedroom, to establish there really is a convective loop going.  Every house is different of course, but I get the smallest deltaT within the conditioned space with the fan on low.  My idea is to piggyback the filters onto the fan that is already running.


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## woodgeek (Nov 4, 2021)

I've played around with manometers and the filter on my whole house return.... I also found that you can buy (used) gauge manometers cheap on FleaBay if you shop a bit, and they are much more accurate/repeatable than water manometers at the required pressures.  I found that a higher quality (and MERV) 3M filter had a lower pressure drop than a cheaper, lower MERV filter.  This confirmed what 3M specs online said, and that my HVAC guy who said my blower would blow up if I put anything heavier than a floss filter in (that I can see through), well, he was full of chit.

I was suggesting that you would want to verify that you were getting the design pressure drop on the filters, to indicate that you were getting reasonable CFM, or reasonable CFM per watt.

I wasn't worried about the motor overheating, I am sure residential fans are thermally over-engineered for things like being laid flat on the floor, etc.  And when a fan is moving less than design cfm, the mechanical load usually goes down (bc output mechanical power is cfm*DeltaP).

If I was going to tinker with your system, I would perhaps make a guard on the intake of your box fan, like a circular hole on the intake side which was a bit smaller than the diameter of the blades.  If the current rig is open over the whole square of the fan (can't tell) you could be getting a lot of recirculation of the air from the blades back into the box due to the back pressure.  Improved CFM could be verified by manometer.


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## Poindexter (Nov 4, 2021)

@peakbagger , @woodgeek , I am glad to have the extra eyes.  I do agree a baffle behind the fan is likely to improve filter effeciency.  Any kind of manometer to estimate filter usage/ indiacte filter replacement would be inexpensive and possibly useful.

However, my goal is to put the best possible air quality into as many homes as possible, as cheaply as possible.  I got to zero PM2.5 without a baffle on the fan.  When the AQ  readings on the $60 meter start climbing, it is time to replace the filters.  When the filters get cruddy and the baby's nose is running again, time to change the filters.

I really don't want to make the filter array more complex or more expensive unless I just can't get to and maintain excellence.

But I do appreciate the pointers.  You both clearly have a better understanding of this process than the average bear.


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## Brian26 (Nov 5, 2021)

woodgeek said:


> I've played around with manometers and the filter on my whole house return.... I also found that you can buy (used) gauge manometers cheap on FleaBay if you shop a bit, and they are much more accurate/repeatable than water manometers at the required pressures.  I found that a higher quality (and MERV) 3M filter had a lower pressure drop than a cheaper, lower MERV filter.  This confirmed what 3M specs online said, and that my HVAC guy who said my blower would blow up if I put anything heavier than a floss filter in (that I can see through), well, he was full of chit.
> 
> I was suggesting that you would want to verify that you were getting the design pressure drop on the filters, to indicate that you were getting reasonable CFM, or reasonable CFM per watt.
> 
> ...


I use the old  school Dwyer Mark ii manometer to measure pressure drop on my hvac filter. Its only like $45 on Amazon and if its helped me save a ton of money on filter replacements. I also found the 3m 1900 Merv 13 to be an incredible filter. It has an extemely low pressure drop and can last for a really long time.  I was also quite surprised how restrictive all the cheap low merv filters were as well.


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## woodgeek (Nov 5, 2021)

Poindexter said:


> @peakbagger , @woodgeek , I am glad to have the extra eyes.  I do agree a baffle behind the fan is likely to improve filter effeciency.  Any kind of manometer to estimate filter usage/ indiacte filter replacement would be inexpensive and possibly useful.
> 
> However, my goal is to put the best possible air quality into as many homes as possible, as cheaply as possible.  I got to zero PM2.5 without a baffle on the fan.  When the AQ  readings on the $60 meter start climbing, it is time to replace the filters.  When the filters get cruddy and the baby's nose is running again, time to change the filters.
> 
> ...



I love a good project, and I am glad that it works for you, and think that many folks without a forced air system could benefit from it.  Waay better than those tiny $$$ 'Molekule' filters in the viral ads.

I just think most people with forced air can simply put a higher MERV (and rated low pressure drop) filter on their system and voila!  Better IAQ.  That was all I needed to do.  Checked the pressure drop against the rated max spec in the air handler manual, and never looked back.

I think this is a case where the 'old guard' HVAC dudes saying 'Don't do it! you will destroy your system' are doing a massive disservice to the general population (lower IAQ and all it implies).   Kinda like the same HVAC guys that talk people out of heat pumps, mini-splits and HPWHs bc 'they don't work' or 'are too expensive' doing a big disservice to the climate.

I have been told all of those things by most of the HVAC people I have let into my house.  Including one old feller recently that I told I was (1) happy, (2) comfortable (3) saving money and that the systems (ASHP and HPWH) had been running happily for years with zero maintenance...and then he told me that I would never be able to sell my house, and that I should tear it all out and put an oil boiler and indirect tank BACK IN.  And then told me that I didn't need to call him again for a '$50 checkup' bc my systems didn't need it!


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## clancey (Nov 5, 2021)

Now that's confusing..lol poor guy--he is retiring I bet --good for YOU....your house price will even be higher have faith..lol clancey


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## begreen (Nov 5, 2021)

Our heat pump air handler was setup with the factory 4" MERV13 filter and I have the 1" 3M MERV13 filter as a prefilter. This is as much for house air filtration for wildfire smoke as it is for winter use when the heat pump runs only occasionally


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## ABMax24 (Nov 5, 2021)

Got my monitor delivered today, so far I'm pretty impressed with it, was sitting at 1-5 ug.m^3 for PM 2.5 when I first turned it on for about an hour, then went outside and lit the pellet grill to cook supper, a little bit of smoke came in the door and right away it hit 76 ug/m^3, basically as quick as you can smell smoke the sensor is detecting it.

Will be interesting to see what it shows over the next few days, and even tonight when I light the stove again.


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## Poindexter (Nov 5, 2021)

@woodgeek, I am not liking this new reply feature with the last software upgrade.  

I stand by my previous advice that typical homeowners should not "upgrade" to a higher filtration filter without professional advice.

However, I do also agree a homeowner with a manometer and a written spec for pressure drop across the filter can run any MERV rating they like as long as they are within the specified pressure drop.


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## Poindexter (Nov 6, 2021)

@ABMax24 , awesome.

Be advised, the little number bottom right corner on the main screen, the "AQI" number on these items  uses the Chinese AQI calculation, which is different from the USA EPA spec (more conservative) and the World Health Organization (WHO) calculation, which is even more stringent.

What I am seeing so far at my house is PM2.5 is almost always the controlling pollutant for calculating AQI.  I am seeing more PM10 with cold starts than I do with hot reloads, but day in and day out PM2.5 is the thing to keep the closest eye on, at least seems to be so far.

In the US, PM2.5 from 0-6 mcg/m3 corresponds to 'excellent' AQI, with AQI numbers 0-25.  6.1 to 12 mcg/m3 @PM2.5 corresponds to AQIs from 26-50, "good" in the USA.


There is a PM2.5 to USA AQI calculator here: https://www.airnow.gov/aqi/aqi-calculator-concentration/ that returns 14 mcg/m3 of PM2.5 as AQI/55 - unhealthy for sensitive groups, aka moderate.

I haven't found a WHO calculator yet, there is a decent wiki article here: https://en.wikipedia.org/wiki/Air_quality_guideline

with this quote



			
				referencedwikipediaarticle said:
			
		

> The guideline stipulates that PM2.5 not exceed 5 μg/m3 annual mean, or 15 μg/m3 24-hour mean;


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## woodgeek (Nov 6, 2021)

True @Poindexter .... I don't advocate everyone just go out and get better filters and install them blind.  I also agree that MERV 13 is plenty for otherwise healthy people with IAQ issues/concerns.

I AM saying that the problem you are aiming to solve (getting higher IAQ in people's homes) is important but was solved many years ago by 3M engineers, who made low pressure drop MERV 13 filters.  And the rollout of that solution, both for existing homes and new construction, has been largely blocked by HVAC technicians, out of obsolete experience and a blind desire to avoid callbacks for any reason.  Those same techs on the HVAC forum that told YOU not to install a MERV 13 on your system.

Sometimes professionals prevent the adoption of simple solutions.

How could this be fixed?  Well, many of those HVAC pros have gauge manometers, and know the nominal cfm and rated max pressure drop for every air handler they install.  If the cfm (per square foot of filter) is below a threshold, and the max pressure drop above a threshold, then they KNOW that a 3M MERV 13 filter is aok and they could just tell the homeowner that.  The govt could help by certifying high filtration filters that have a pressure drop below some threshold as 'gold rated' or something.  The HVAC guy says, you can put any filter in that had a 'gold rating'.  DONE.

I am telling you that 100% of the air handlers installed in the last 10 years can handle these filters....they have LOWER drops than the low MERV filters from 20 years ago.

Have an ad campaign 'Have an IAQ problem, call your HVAC guy for advice'.  Your HVAC guy get s a damned callback and then googles your air handler part number, and replies 'Yeah, you can put in a gold filter' perhaps without even setting foot in your house, if he has the install info.

Folks doing an energy retrofit (often free from their utility)... well IAQ is ON THEIR LIST of improvements.  They could do the checking of air handler specs, pop in a gold filter, give the homeowner a years supply free, and tell them 'only put in filters with the gold label rating'.  As it is, they are giving some homeowners freestanding HEPA filters with expensive filters, that only treat one room, and which cost way more than a years supply of filters.

I am sure we will get some version of the above someday....when HVAC pros start to see IAQ as a serious, rather than nuisance, issue.

In the meantime, your box is a happy solution, and waaay better than the tiny boutique and super spendy 'air purifiers' being sold for hundreds of dollars.


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## Poindexter (Nov 6, 2021)

@woodgeek , you clearly know way more about HVAC systems than me.  I am simply not equipped to even attempt a peer to peer discussion with you, because I don't have the background to be considered your peer by any reasonable standard.  Thank you for sharing your perspective.

I don't have any duct work in my home, except for the courtesy fan in each bathroom.

My wife's office does have forced air, and some mold in the ductwork.  There is no visible labeling regarding MERV rating or pressure drop that I could find anywhere on the system near the filter.  I did find three new filters in the furnace closet, so replaced the filter that had been in use for 6-7 months.  Filter size is nominal 15x30x2, no printed MERV rating but visually less than MERV13.  Building is more than ten years old.

Right now I have another $700 worth of particle counters inbound.  When they get here I am going to have to run them a while all on the same table to see how close they read to each other, then I can start taping them to the walls in my hallway to see where the PM2.5 goes between leaving the open loading door of the stove and arriving at the filter array.

Once that is done I can rent a PID or FID VOC detector and go looking for VOCs in my house.

I share your dismay at the expensive room size air cleaners.  They are expensive up front and often use expensive proprietary shaped filter media.  I have two of them retired in my garage.  Both were noisy, as team the both of them could not keep up with my 1200sqft home, and I was able to get three furnace filters  cheaper than I could have replaced the filters in those two units.

I did build a somewhat prettier unit for my wife's office building.  She only has room for it in her office in a corner during the day.  After hours she pushes it out into the hallway and runs it on high overnight.  Filters on two sides and the bottom, weatherstripping under the fan for sealing.  If someone wanted to they could go bananas with birdseye maple, a french rub finish and maybe some speaker cloth over the filter media to make it look like a big subwoofer.  I used baltic birch plywood, spray shellac and got the item into service.

My immediate goal is cheap, simple to make and effective.  Make pretty is not on my current list of things to do.


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## woodgeek (Nov 7, 2021)

Passing the wife test is usually the biggest hurdle.    

The birch one looks great.  And the circular exit hole should boost performance by blocking recirculation.

I await your results on VOCs.  I haven't come up with a decent solution for that in my place.... I played around with activated carbon media, but never got a VOC detector or data.


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## semipro (Nov 7, 2021)

I recall seeing a very basic version of this being built on This Old House.




I agree that using centrifugal (squirrel cage) instead would be a great upgrade.  It looks like someone built something similar to your wood version that serves double duty as a work surface.  I like that.




I do recall some past concerns about using a  similar filtration system in a dusty area like a woodshop where the increased airflow can stir things up and actually decrease air quality with respect to particulate exposure to workers.  This may be why most shop operators focus on particulate extraction at the generation source rather than whole room air filtration. 
There's a somewhat dated discussion about this issue here.


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## Poindexter (Nov 7, 2021)

Thanks for your input so far everyone.  

I am deliberately choosing to not respond in to this tread for a while.  My ongoing results are good.  The trouble is if I continue to blab here then scholarly journals will be less interested in re-publishing data that is already in the public domain.

Once the data is either published or rejected, then I can preach it, either with or wthout a footnote. 

Thanks for understanding.


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## semipro (Nov 7, 2021)

Please share your citation with us when you get published.
Personally, I worry far more about VOCs and radon in our indoor environment.  I feel like our bodies are better equipped to handle particulate matter with nasal and bronchial cilia, mucous, expectoration, etc.   I don't feel as comfortable letting my body's natural defenses handle VOCs like formaldehyde, naphthalene, etc., and radon. 
Incidentally, I'm fairly certain I suffered from a minor case of naphthalene "poisoning" at work two weeks ago when mothballs were liberally spread around to deter snakes entering our office.
Also, our selves, our pets, and our clothes are constantly shedding particulates that get airborne.  Other particulates are constantly kicked up from the floor and spit out by candles, cooking, etc.  I'm always struck by this when I see the stuff floating around in a sunbeam.  It's hard to imagine a particulate-free environment even with extensive filtration.


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## Rusty18 (Nov 7, 2021)

So there I was trying to figure out how to implement this idea into a ceiling fan when she saw my sketches.  I don’t think it’s going to make it past the design stage. 
However I do have 3 filters and a box fan that will be assembled some time this week.  Been needing an air filter for a while now.


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## ben94122 (Nov 8, 2021)

Pardon my ongoing ignorance: how do the washable/reusable electrostatic filters compare with the disposable filters?


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## semipro (Nov 8, 2021)

ben94122 said:


> Pardon my ongoing ignorance: how do the washable/reusable electrostatic filters compare with the disposable filters?


The one we've been using for years is rated as FPR 4 / MERV 8 by the manufacturer.  

An explanation of MERV from Grainger here.


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## sloeffle (Nov 9, 2021)

My furnace came with a 2" thick MERV 11 filter so that's what I've always run on it. 

I use to run the garbage see through filters on my wood furnace. My house was always very dusty in the winter time. I switched to a decent MERV rated filter and the house is much cleaner in the winter time now.


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## Rusty18 (Nov 9, 2021)

Ran out of tape before I got it all sealed up but it’s still moving a lot of air through the filters.


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## begreen (Nov 10, 2021)

sloeffle said:


> My furnace came with a 2" thick MERV 11 filter so that's what I've always run on it.
> 
> I use to run the garbage see through filters on my wood furnace. My house was always very dusty in the winter time. I switched to a decent MERV rated filter and the house is much cleaner in the winter time now.


We have a 4" MERV 13 filter on our heatpump air handler. I added a 1" MERV 13 prefilter this year in anticipation of wild fire smoke that didn't happen.


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## EbS-P (Nov 11, 2021)

I think a great improvement would be and easy to build diy shroud for the standard 20” box fan.  Squirrel cafe may be better but it’s about what you can get cheap at Amazon or your local hardware store.  Off the shelf items that can easily be repurposed is what I’m thinking.  Next time at the hardware stores I’ll take a stroll and see if any ideas come to me.  

Ideally it would be more aerodynamic than just a circle and be rigid enough to maintain some minimum clearance to the blade tips.


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## Brian26 (Nov 11, 2021)

I'm on solar but here in CT with some of the most expensive electricity rates in the US it could make a difference. If one of those box fans with 3 filters is pulling a 100 watts or more it could cost a substantial amount of money to run nonstop for a month.


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## Rusty18 (Nov 11, 2021)

Brian26 said:


> I'm on solar but here in CT with some of the most expensive electricity rates in the US it could make a difference. If one of those box fans with 3 filters is pulling a 100 watts or more it could cost a substantial amount of money to run nonstop for a month.


Google says the 3 speed lasko pulls 55 watts on high.


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## semipro (Nov 11, 2021)

Brian26 said:


> I'm on solar but here in CT with some of the most expensive electricity rates in the US it could make a difference. If one of those box fans with 3 filters is pulling a 100 watts or more it could cost a substantial amount of money to run nonstop for a month.


I have that concern too so I install filters on many devices in our house that move air.  
Firstly, it turns these devices into air filtration units, and secondly, it keeps their innards clean.  
Solar inverter, HP clothes dryer,  fridge,  freezer, desktop computer, HPWH, portable electric heaters, etc.


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## ABMax24 (Nov 11, 2021)

So I've been watching the air quality monitor over the last few days, and if it is accurate the air quality within my house is very good, especially considering we are utilizing a wood stove. Generally it sits at an AQI of 0-1 with the odd time it goes to 5. Cooking has by far the largest impact on our air quality, it's not uncommon to see spikes to 20 while preparing meals.

It is very uncommon for us to have a wood smoke smell in the house from our stove, I attribute much of this to the high draft our 36ft of chimney provides, opening the flue damper prior to opening the door creates such an inrush of cool air into the stove that nothing can escape. Another factor is we don't have an OAK, the stove consumes the stale air from within the house to be replaced with cold fresh air from outside. I'm thankful to live in an area with generally good air quality in winter, so bringing pollutants in from outside isn't much of a concern.

We do have a 3M filtrete 2200 filter in the furnace that does help with air quality should it deteriorate, although I like to use it sparingly as the blower pulls 700 watts while on.


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## Brian26 (Nov 11, 2021)

semipro said:


> I have that concern too so I install filters on many devices in our house that move air.
> Firstly, it turns these devices into air filtration units, and secondly, it keeps their innards clean.
> Solar inverter, HP clothes dryer,  fridge,  freezer, desktop computer, HPWH, portable electric heaters, etc.


I have a Winix  air purifier that appears to have a brushless DC motor on a squirrel wheel style fan.  I was curious how much power it used so connected a killawatt to it. I was surprised how little electricity it used. On low it was moving a good amount of air and only drawing less than 10 watts. I think even at full bore it was only like 25 watts.  This unit also has a particle sensor and will ramp up and down the motor depending on the air quality.


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## EbS-P (Nov 11, 2021)

Brian26 said:


> I have a Winix  air purifier that appears to have a brushless DC motor on a squirrel wheel style fan.  I was curious how much power it used so connected a killawatt to it. I was surprised how little electricity it used. On low it was moving a good amount of air and only drawing less than 10 watts. I think even at full bore it was only like 25 watts.  This unit also has a particle sensor and will ramp up and down the motor depending on the air quality.


Mine alerts  me to every fart, human or canine.  I could do with out that feature on the homebrew version.  My nose works good enough.


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## begreen (Nov 12, 2021)

EbS-P said:


> Mine alerts  me to every fart, human or canine.  I could do with out that feature on the homebrew version.  My nose works good enough.


The only thing that regularly triggers ours is when something is being fried in the kitchen.


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## EbS-P (Nov 20, 2021)

I have been using these washable filters as pre filters for my hvac and got another for my MERV 13 box fan filter.  I feel like it extends my filter life considerably as I can wash every couple weeks.  And they are cheap. 

Just some thoughts. 
20-in x 30-in x 1-in Cut to Fit Adjustable Air Filter https://www.lowes.com/pd/Filtrete-20-in-x-30-in-x-1-in-Cut-to-Fit-Adjustable-Air-Filter/5005517111


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## peakbagger (Nov 21, 2021)

One somewhat sad observation over the years is that pets can really reduce indoor air quality. Open up any piece of equipment with air flow in it like a mini split indoor head and if its in house with pets, it going need to be cleaned. If its house without pets its going to be a lot cleaner. Same goes with homes  with smokers but luckily that habit seems to slowly dying out.


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## EbS-P (Nov 21, 2021)

peakbagger said:


> One somewhat sad observation over the years is that pets can really reduce indoor air quality. Open up any piece of equipment with air flow in it like a mini split indoor head and if its in house with pets, it going need to be cleaned. If its house without pets its going to be a lot cleaner. Same goes with homes  with smokers but luckily that habit seems to slowly dying out.


Pets (and kids) are dirty hence my washable pre filter.


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## SpaceBus (Nov 21, 2021)

We have decided against indoor pets in the future, just to improve our indoor air quality.


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## semipro (Nov 21, 2021)

With 4 dogs and a cat that live in and out, we fight a constant battle against hair.  We think it's worth it given the companionship and protection they provide. 
We have an army of vacuums and other air filtering devices throughout our home including one brave little robotic vacuum that deserves a medal.  Even our fridge functions as an air filter as I installed a washable filtering element at its air inlet. It also keeps the condenser clean.
Given the size of hair and dander, I'm more concerned about the smaller particles like smoke and soot that seem to be the cause of most respiratory problems as they make their way past our bodies' defenses and embed themselves in our lungs. 
We no longer burn candles or incense.


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## SpaceBus (Nov 21, 2021)

semipro said:


> With 4 dogs and a cat that live in and out, we fight a constant battle against hair.  We think it's worth it given the companionship and protection they provide.
> We have an army of vacuums and other air filtering devices throughout our home including one brave little robotic vacuum that deserves a medal.  Even our fridge functions as an air filter as I installed a washable filtering element at its air inlet. It also keeps the condenser clean.
> Given the size of hair and dander, I'm more concerned about the smaller particles like smoke and soot that seem to be the cause of most respiratory problems as they make their way past our bodies' defenses and embed themselves in our lungs.
> We no longer burn candles or incense.


Don't get me wrong, I love our dogs, but they are the last indoor dogs. I'm just to the point in my life that I don't want to vacuum three times a day and run a bunch of filters almost constantly. We recently invested in a "smart" filter with a air quality sensor. When our dogs play or pace around the room the air filter turns on. Sometimes it will turn on if my German shepherd walks too close to the filter. It doesn't help that our home isn't very large and the dogs have about 600 sqft of kitchen/living area, which isn't a that big, especially with furniture, counters, stoves, etc. We had different living arrangements when we first got the dogs, but that was also ten years ago. It's all a give and take, and we just don't think it's worth it for us anymore. If we didn't have 35 animals living on the property and never any mud I may feel differently. I'm not ruling out any dogs in the future, they would have to be working dogs and live outside though.


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## Rusty18 (Nov 21, 2021)

Umm are you all aware dogs can not survive outside?  Well unless they have a heated kennel, heated water bowl, heated bed, and hot meals twice a day...I lost that argument two years ago.  The “dog house” is nicer than some places I’ve lived.  
On a serious note, there are some designer breeds (see mutts) out there that shed very little/not at all.  Helps with the hair in the house greatly, they are usually smaller breeds so better for a smaller house too.


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## SpaceBus (Nov 21, 2021)

Rusty18 said:


> Umm are you all aware dogs can not survive outside?  Well unless they have a heated kennel, heated water bowl, heated bed, and hot meals twice a day...I lost that argument two years ago.  The “dog house” is nicer than some places I’ve lived.
> On a serious note, there are some designer breeds (see mutts) out there that shed very little/not at all.  Helps with the hair in the house greatly, they are usually smaller breeds so better for a smaller house too.


I have livestock, none of my animals live without a shelter. If we got an outdoor dog, it would be a working livestock guardian dog that lives with our livestock, not just wild like a coyote   My German shepherd would love to live outside and roam wild, but my alpacas don't like him and he isn't trained. Our indoor air quality is great, it just takes a lot of work when you have dander producing animals living indoors.


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## Brian26 (Nov 29, 2021)

Just saw that Lowes has the good Filtrete 1900 filters on sale. 20% off when you buy 4. I just went to my local store and stocked up.


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## lml999 (Dec 20, 2021)

I spent some time reading this thread as I'm concerned about IAQ. I've been burning for about ten years (two different houses) with an Enviro 1200 insert and lately, it seems, I get a good puff of smoke into the house every time I open the stove door. My wife has asthma and I'm concerned about the impact of IAQ on her and my health.

I run two HEPA air filters in the house, one in the room with the stove, and a second upstairs (traditional colonial). I also have an HRV that pulls air from the  (far end of the) room with the stove and has a MERV 13 filter installed. It returns the air via an inlet near the stove.

There's a new toy running around, sucking the dirt. dust (and dog hair) from the carpets and hardwood floors.

I just ordered the $60 IAQ meter from Amazon, will play with it for a while.

A home built cube fan/filter will have very low WAF. Moving to Florida (from New England) is higher on her list.

So...here's the question...from a health standpoint,  am I crazy to be burning?

Yes, I know, this is a provocative question, but in all other parts of my/our lives, we typically choose the healthy option...good diets, safe cars, exercise, etc.


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## tlc1976 (Dec 20, 2021)

It depends on what makes her asthma act up. I have asthma among many other things, and for me it’s crazy to have animals in the house, especially cats. No issues with burning firewood or pellets or even the cleaning procedure.


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## Rusty18 (Dec 20, 2021)

lml999 said:


> I spent some time reading this thread as I'm concerned about IAQ. I've been burning for about ten years (two different houses) with an Enviro 1200 insert and lately, it seems, I get a good puff of smoke into the house every time I open the stove door. My wife has asthma and I'm concerned about the impact of IAQ on her and my health.
> 
> I run two HEPA air filters in the house, one in the room with the stove, and a second upstairs (traditional colonial). I also have an HRV that pulls air from the  (far end of the) room with the stove and has a MERV 13 filter installed. It returns the air via an inlet near the stove.
> 
> ...


Yes.  Now for the rest of the story...is wood burning a hobby or a necessity for you/your wife?  Is the dog a necessity or a luxury/comfort?  Everything in the life has a price, only the purchaser can determine if it’s worth it.  (Please don’t assume price =$$)  our 6 month old is battling a stuffy nose so I’m not burning just to help keep the IAQ as high as I can, (not saying it lowers IAQ that much but right now I’m not willing to add any unnecessary particulate to the air).  However if I needed to fire up the wood stove to keep the house warm it’d be lit right now.  Necessity vs hobby with a slight sprinkle of unmeasured risk.   I think you’re on the right track with the air monitor, it will either put your mind at ease on the current IAQ or it will give you a base line and you can track down any offendering particulate emitters (stove or otherwise).
Good luck.


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## lml999 (Dec 22, 2021)

Rusty18 said:


> Yes.  Now for the rest of the story...



Thanks...

Burning is a hobby. We live in a well-insulated, tight traditional colonial, heated by gas.

The dog is a cavachon, pictured to the left, with hair rather than fur, hypoallergenic. He has never been an issue for my wife's asthma, which only pops up in cold months.

I have split hardwood delivered and pay $200-350 a cord for the privilege. I occasionally have wood to split, but might represent 10-20% of my wood supply.

I don't think I'm saving a substantial amount of money by substituting wood for gas. Saving money would be nice, but isn't a driver. When we heated with oil, we took several thousand dollars a year off our heating bills with the stove.

It's a hobby I like a lot, and my wife likes the comfort of a warm fire. But if it's causing her asthma to flare up...

She believes that it's the cold weather that affects her asthma. IDK how much, if any, a potential IAQ issue is making things worse...


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## woodgeek (Dec 22, 2021)

lml999 said:


> Thanks...
> 
> Burning is a hobby. We live in a well-insulated, tight traditional colonial, heated by gas.
> 
> ...



It seems to me that she would have a sense of whether the burning is triggering her asthma, if you are only doing it sometimes.

Also, think about wood storage....firewood could contain mold spores or other allergens.  IF so, you could get a closed wood box, store the wood in the garage, etc.


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## Rusty18 (Dec 22, 2021)

Something else to consider, humidity.  If you aren’t measuring it indoors you might want to.  I’ve got two humidifiers running, one is a wick type that will evaporate about 3-4 gallon a day on high and a hot mist one in the bedroom that will burn about 2 gallon when it’s clean (see hard water issues).   When heating on electric they struggle to keep house 55-60 range, when I fire up the wood stove I add a pot with water to the top to help out.  With the wood stove on I can’t keep the humidity above 50, below 50 we all have a noticeable deterioration in sleeping ie waking up with scratchy throat/coughing, irritated nose etc.  The 6 month old is affected the most.  In my case I don’t think I’m getting issues from smoke/particulate because it’s not cold enough to do a reload, just a packed full top down and let it go cold.  We both forgot to fill the wick type last night before bed and it went dry, this morning was 46% in bedroom and 40% in the rest of the house.
I guess the short version is wood stove may be driving your humidity so low that’s cause part or all of her issues in the winter.


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## tlc1976 (Dec 22, 2021)

Do you usually open windows to get some fresh air when it’s not cold outside? It might be the lack of fresh air in a tightly sealed house.

Since gas is not totally prohibitive for you, you could try just gas for awhile, no fires, no wood…. and see if it helps her. That might help determine if it’s the fire/wood or not.


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## lml999 (Dec 26, 2021)

As mentioned above, we have an HRV and two HEPA air filters. *Sometimes* if the stove and chimney is cold I have to open a window briefly when starting up the stove.

So...I got the AIQ device, and it's showing that our air quality is NG. Moderate to heavy air pollution when the stove is running. It clears to good if the stove stays closed and burns down overnight. The device is on the second floor in our bedroom, pretty far away from the stove.

I definitely have an issue...every time I open the stove door (Enviro Kodiak 1200 insert), I get a stream of smoke out. Doesn't matter whether the fire is new or well established.

I think I have a pretty significant draft problem, will not be using the stove until my local chimney sweep (who installed the stove a couple of years ago) can take a look. I called today...expect that they will be here by early/mid week.

I expect that I will get yelled at for not burning fully seasoned wood, but even seasoned wood is smoking up the room. Perhaps it might be more complicated than that... I will report back.


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## Rusty18 (Dec 26, 2021)

well that sucks but at least you have confirmed there is a problem, have a means with which to measure progress on the issue, and are taking steps to fix the problem.


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## Rusty18 (Dec 26, 2021)

Sounds like you have a draft issue for sure, hopefully a good chimney cleaning will get you back in business.


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## lml999 (Dec 26, 2021)

Agreed. Curious to see the IAQ measurement after the flue is cleaned, or whatever else needs to be done...

Also, curious to take the IAQ meter into my woodworking shop, where I run a dust collector and two midsize WEN filtration systems.


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## lml999 (Dec 26, 2021)

Poindexter said:


> This is pre-pub. I have a lot of documentation to do after I collect a bale of data. I wasn't expecting to post here for another 6-8 weeks, but check this out.



Thanks again for your work and the mention of this IAQ meter. I got one earlier this week and it seems to be working quite well. I was surprised at how compact it is!


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## Rusty18 (Dec 26, 2021)

The box took up too much space and made too much noise to be left in the middle of the living room but it did make a noticeable difference in the dust level.  Long story short I “made” the filter fit in the hvac system right above the hog hair filter (I guess those were put in to keep the odd Racoon from getting sucked into the coils cause they sure ain’t stopping anything else).  That’s about 3 weeks worth of run time.  Soon as I get a free minute I’m getting out the tin snips and making a tray to hold a 20-20-2 and doing away with the old filter. 
The sunbeam through the window particulate monitor also supports the reduction in dust floating about too.

No pets inside but they do keep the porch dirty, barn shoes/boots get left in the garage so not making a bunch of dust, just haven’t filtered any out since we moved in in ‘18.


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## lml999 (Dec 29, 2021)

Rusty18 said:


> Something else to consider, humidity.



Yea, humidity. Haven't been burning for a couple of days, have a cleanout scheduled for Monday.

In the meantime, my IAQ meter really doesn't like my Air-O-Swiss ultrasonic humidifier. I've cleaned it, started using filtered water, and while it's running, the IAQ reports unhealthy air.  The humidifer is on the second floor landing, blowing over the first floor entrance hallway. The IAQ meter is in our bedroom, 15' from the humidifier. 

Not long after the humidifer runs dry and stops, the IAQ readouts drop nicely. So I don't know whether it's something in the filtered well water or the moisture in the air itself that's driving up the IAQ readings.

...just to complicate matters, right?


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## woodgeek (Dec 29, 2021)

lml999 said:


> Yea, humidity. Haven't been burning for a couple of days, have a cleanout scheduled for Monday.
> 
> In the meantime, my IAQ meter really doesn't like my Air-O-Swiss ultrasonic humidifier. I've cleaned it, started using filtered water, and while it's running, the IAQ reports unhealthy air.  The humidifer is on the second floor landing, blowing over the first floor entrance hallway. The IAQ meter is in our bedroom, 15' from the humidifier.
> 
> ...



I believe it.  I am not a fan of those at all.

The ultrasonic formed droplets are of mineral laden water, which after evaporation makes a 'white dust' mineral microparticle, which an IAQ meter will certainly detect.  After using such humidifiers in my bedroom for a few years, I discovered I had become sensitized to the dust, and got nasty sinusitis reliably when we used it.  I switched to a wick based evaporative unit (which I keep clean with a bacteriocide) and my problem went away completely.

When I experimented with an oil diffuser, I ran distilled water for this reason...but not practical for home humidification.


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## Rusty18 (Dec 30, 2021)

Well shoot, I’ve got a hot mist one in the bedroom (not ultrasonic) that I have to clean weekly (not so soft soft water).  You’ve  got me wondering if that may be part of my problem now!


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## lml999 (Dec 30, 2021)

Rusty18 said:


> Well shoot, I’ve got a hot mist one in the bedroom (not ultrasonic) that I have to clean weekly (not so soft soft water).  You’ve  got me wondering if that may be part of my problem now!


Yes, you might be quite surprised. I haven't run the humidifer in 24 hours and the current reading is 0 ppm. 24 hours ago it was reading in the red, quite literally.


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## NorMi (Dec 30, 2021)

I never had a problem with evaporating water on the stove, hot mist, wick style, or now the Venta style I just got, but the ultrasonic when used with tap water was a IAQ disaster!


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## stoveliker (Dec 30, 2021)

lml999 said:


> Yes, you might be quite surprised. I haven't run the humidifer in 24 hours and the current reading is 0 ppm. 24 hours ago it was reading in the red, quite literally.



But you use an ultrasonic one. This shoots small droplets into the air, which includes the minerals. After the water of the droplets evaporates, the mineral dust remains aloft.

The hot mist one of Rusty  instead evaporates the water (I think), leaving the minerals behind, and should be much cleaner for the air.

Edit: Consistent with NorMi's observation.


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## Rusty18 (Dec 30, 2021)

stoveliker said:


> But you use an ultrasonic one. This shoots small droplets into the air, which includes the minerals. After the water of the droplets evaporates, the mineral dust remains aloft.
> 
> The hot mist one of Rusty  instead evaporates the water (I think), leaving the minerals behind, and should be much cleaner for the air.
> 
> Edit: Consistent with NorMi's observation.


Yes, it has a heating element that boils the water. Have to clean out a golf ball size chunk of minerals about once a week.
Just wondering if the boiling action is not sending some of the mineral laden water air borne similar, but to a much lesser degree, to the ultrasonic.   Guess I need to take my own advice and get something to measure IAQ.


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## peakbagger (Dec 31, 2021)

Years ago,I used to have to babysit a computer room HVAC system. The temp and humidity had to be controlled pretty carefully. The humidifier was a pan with an automatic level control with a timed bottom drain. There was infrared heater over the pan that turned on to give off water vapor into the air stream. It worked pretty well; the auto drain kept the minerals from precipitating into the pan. The trade off was those infrared coils were not free to run.


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## Poindexter (Jun 28, 2022)

So data.  Yay!!  I did get hooked into a group of kids at USC researching air quality and... nothing.

Briefly, running 3 MERV13s  on a 20" box fan as pictured on page one I, like ABMax, routinely see 5-6-7 mcg/ cubic meter for raw PM2.5  count- in the stove room while my wood is running, and 12-15 mcg/m3 in stove room while cooking in the kitchen.

New problem this week, wildfire smoke.  My raw outdoor PM2.5 count this morning was 189, a few minutes ago it hit 482 mcg/m3, highest reading I have ever seen.  The highest one I remember before today was a raw PM2.5 count of 364 mcg/m3 last summer, also during wildfire season.


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## Poindexter (Jun 28, 2022)

I shall not comment on EPA's displayed commitment to my pulmonary health while unseasoned wood is on fire and the smoke is on my lawn.

With all the windows in the house shut, and a 3 filter Poindexter box running upstairs on low, observed raw PM2.5 count was 24-25-26, right on the cusp between good and moderate.  

I shan't I shan't I shan't.  I will go kick some puppies and come back with other observations in a few minutes.


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## EbS-P (Jun 28, 2022)

Glad to see this. It reminded me I have a washable MERV 13 and a box fan sitting somewhere that never actually got built.  I should go find those.   We have several days a year with controlled burns around here.  It can be smoky when the the University burns basically my 300 acre+ backyard.  Then all the “Plantations” annually burn the understory but usually something gets out of hand and we end up with ash falling all over town.   Need to go clean my heap filters.


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## Poindexter (Jun 28, 2022)

FWIW I am in a nondescript suburban box shaped house, 1200sqft upstairs, and another 1200 sqft downstairs.  No filter running downstairs.

In my garage I have a boiler for the hot water baseboard heat, and a loop in the boiler for DWH.  I am reliably informed I am burning about one gallon of oil daily to make DHW and maintain the boiler core at 160dF/20psi.  I do not know how many cf of air I am bringing in daily to combust the oil, but clearly some.

Top right, the four inch stove pipe that goes over and up is the combustion air intake for the boiler.  As expected, observed AQ in the garage was 'worse' than upstairs, but I also have in stock a double decker P-box, six filters, one 20" box fan.  Garage volume is about 2000 cuft.


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## Poindexter (Jun 28, 2022)

The double decker is mostly for controlling sawdust from my woodworking hobby, but the lineage of the Pbox draws heavily on wildfire smoke abatement on the Corsi-Rosenthal side of the family tree.  The three filter system has done well, the six filter system took some names this afternoon.  Two of the eight openings on the double decker are covered with 20x20 plywood panels duct taped in, so 6 MERV 13 filters, one 20" Lasko on top blowing up.

Given the time stamps on the photos, the double decker with the fan on high, nominal 1000cfm, brought the garage to here in 6 minutes.


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## Poindexter (Jun 28, 2022)

The downstairs of the home is roughly half and half garage and living space, the living space includes 2 bedrooms, 1 full bath, a hallway and a stairwell.  I moved the double decker from the garage into the downstairs hallway.  I didn't take photos in the moment.  When I got home, raw PM2.5 count in my office was 122 mcg/m3.  Right now, with the double decker running out in the hallway less than one hour, the raw PM2.5 count in my office is 21 mcg/m3 and dropping.

Upstairs I bumped the fan on the Pbox from low up to high and moved the needle on the raw 2.5 count from 25 to 7 in about 45 minutes.

Observations:
1. The Utilitech (team orange) box fan is a noisy little beastie that moves about the same cfm as a Lasko, but makes a great deal more fuss about doing it.
2. MERV 13 filtration is very effective filtration for baseline healthy people facing wood smoke.


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## begreen (Jun 29, 2022)

The AQ improvements are impressive. The result is better than outside air which often is not the case in modern homes.


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## Poindexter (Jul 4, 2022)

The wild fire smoke continues.  There were two work days last week where I was running my headlights on the freeway so other drivers could see me coming, and no sunglasses required.

We have pretty much been running 125-250 mcg/m3 for (outdoor) PM2.5  for going on two weeks now.  We have a really big fire to the east, and another one to the west, so change in wind direction doesn't really help us.

One thing Alan and David and I haven't been able to agree on is filtering particles less than 2.5 microns.  I think, and I only have a little data, that running air through a filter slower lets more of the tiny's (0.3 and 0.5 micron) get trapped in the filter media. 

As an aside, I ran four of the $60 units from Amazon and two of the $$ Dylos devices side by side for two events, and the $60 unit correlates well.  The less expensive unit is going to be within a particle or two of either of my Dylos units from about 4mcg/m3 up to 200+ mcg/m3.  Under 4 mcg/m3 your AQ is excellent and it doesn't matter.  Above 200mcg/m3, you shouldn't need a meter to know you have a problem.

So here is my office right now.  I am running the double decker pictured recently, 6 of 20x20 MERV 13 filters, with the Lasko fan on low, in 600sqftof floor, about 4800 cuft downstairs.  The velocity of the air through each filter is not known, but it should be 1/6 of total fan throughput average.

In this moment, my nearest EPA certified AQ monitor is showing 112mcg/m3 for PM 2.5 outdoors.


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## Poindexter (Jul 4, 2022)

We did open the windows this morning to let in some cool air, but left them open when we left for church, and then we took another couple to lunch after church, should have closed the windows before we left, I came home to 122 mcg/m3 in the upper level of the house, 1200sqft x 8 ft ceilings, about 9600 cuft.

I am currently running a single box fan with a single MERV 13 taped to the front of it upstairs.  The P-box (3 filter) I did have upstairs went to my office when my employer, well anyway, the air quality at my day job office is good.

With the single box fan (on high) pushing through a single MERV 13 (3M filtrete model 2200) filter for close to 6 hours,  upstairs AQ is these:


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## Poindexter (Jul 4, 2022)

I fully understand wife approval factor (WAF) is an important parameter in every home.

I am, one data point, getting better absolute results with a relative muchness of filter area and low fan speed.  

Engineers will insist filter efficacy is a function of both time and effectiveness, how fast can the filter clean the air.  I can see this for industrial processes with point located and time limited sources of pollution.  Like welding a car body together 4x per hour or unloading a grain ship once a week.

Wildfire smoke, and wood stove smoke, and cat dander are all ongoing sources of pollution.  My problem is keeping the air clean, not getting the air clean after a one time event.  For my process, my challenges, I prefer a low fan speed with plenty of filter area.


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## EbS-P (Jul 4, 2022)

Smaller than 2.5 particles the physics is just different.       Electro statics play a really big role for the small particles.  First decent link that google gave me.  Can’t say I read it. I did look for important bits.    Looks like there is a size of particle that has a minimum filter effectiveness.  Both smaller and and larger particles are easier to capture.  





						Particle size for greatest penetration of HEPA filters - and their true efficiency (Technical Report) | OSTI.GOV
					

The U.S. Department of Energy's Office of Scientific and Technical Information




					www.osti.gov
				




Velocity is mentioned too.


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## Poindexter (Jul 4, 2022)

Thanks @EbS-P .  All I can get from home is the abstract, I will see if I can open that from inside my work network Tuesday.

I am building a new P box for home use, should have it up and running in a week or so.

The original in post one this thread exceeded expectations.  I had excellent air quality all through my heating season, except our indoor AQ dropped to good while we were cooking in the kitchen, same as @ABMax24 found .

There are two issues I am addressing with the second build.  

1. With filters on left, right and rear, the original P box cannot be shoved up against a wall without blocking off one of the filters.  To address this, I am putting the new build on casters to lift it up off the floor.  I will be able to mount one filter element in the bottom, and place a blank panel on one of the sides, so Pb2 can be shoved against a wall.

2. Our cat spent a great deal of the winter sleeping on top of Pbox1.  The cardboard top secured with duct tape made it through the heating season, but the tape was needing to be firmly pushed back down every 2-3 days as pollen season was spooling up.  So I am making Pb2 out of plywood.  My cunning plan is to put a cat bed up there.  She will either knock it off and sleep on the bare plywood, or go somewhere else to nap.

At this juncture I explicitly reiterate all you need for excellent IAQ is a box fan, the box the fan came in, 3 MERV13 filters at 20x20x1 inch, some duct tape and a sharp knife.  And dry wood and no draft problems, but let us not skid off into the weeds.  As pictured in post one, you can use the box fan to establish a convective loop in your home and clean your air at the same time.

An alternative, if you have a big enough box from Amazon, would be to make top, bottom and one side from cardboard and only buy two furnace filters.  Between wintertime wood stove, spring pollen and summer wildfire smoke I get about one year and have to replace three filters.  Two filters should work, just not last as long.  Or you could set two filters behind the fan to make a triangle and then cut a triangular top and bottom from the box the fan came in.

I am building Pb2 from plywood so in the future all I have to do is replace the filters annually, not rebuild from scratch every year.

I am putting in a baffle between the filter box and the fan intake, and I beveled the filter side of the baffle with a quarter inch roundover router bit.  This is NOT necessary for excellent indoor AQ.  It is a thing I am doing while I am starting with a fresh sheet of plywood that should make the finished item incrementally more efficient.  I doubt I will find a measurable increase in performance, but this should last 20 years and it would bug me to not do it.


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## EbS-P (Jul 4, 2022)

Trying to attach the pdf


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## Poindexter (Jul 7, 2022)

A good news/ bad news sort of day.

My upward blowing box passed electrical safety inspection today and is now in 24/7  use at the hospital I work for- in a non clinical area.  Under construction it made an appearance in post 26 this thread, page two in my browser.  AQI at my hospital office was unhealthy when I arrived this morning, it was down to unhealthy for sensitive groups at the end of the day and I am looking for good/excellent in the morning.

When I internet search on "passive solar firewood kiln" I hit five threads at this forum, and a picture of my back yard, on page one of search results.  When I internet search on "good indoor air quality cheap" this thread doesn't appear in the first ten pages of search results.  Not sure what to do about that.  If the man is out to get me he doesn't have the cojones to just ring my doorbell.


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## Rusty18 (Jul 7, 2022)

I think your kiln thread has been around longer/ has had more activity than this thread?  Of course if everyone on here googled it by it’s thread name we could probably get it to the top of the list a little quicker too.  

Back in 2007 when I was at WVU one of the teaching assistants made a wiki article on the weight of the walkway going to the main engineering building and searched it enough times to get it to the top of googles list.  One of the freshman projects was estimating the weight of the bridge.  It made it real easy for him to figure out who actually put some thought into it and who “googled” it.


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## begreen (Jul 9, 2022)

Yes, it takes time to build hits up. I will add Homemade air filters - to the title which may help improve search engine hits. However, unlike solar kiln, there are so many articles and videos on this topic that the competition is stiff. 

PS: Sorry to hear about the wildfires. AK and Siberia have been getting more of them and with the vastness of the wilderness, it's hard to fight them.


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## Poindexter (Dec 7, 2022)

It has come up twice recently in different threads.

On two occasions winter 21/22, with medical grade respiratory PPE and the wife not home, I left the loading door of my running woodstove open long enough to run my particle counts in the stove room up to (PM2.5) 300 mcg/m3.  This is more or less the level of pollution found or stated in the oft quoted article from the UK news source _The Guardian_, and is a stupid amount of poor indoor AQ.  

I have found that I cannot see or sense 'bad' or 'poor' or 'affected' AQ until my particle counters are showing PM2.5 around 125 mcg/ m3.

However, on both occasions, I was running 4 of the $60 particle counters from Amazon as pictured often in this thread, and two Dylos 1100 Pro side by side by side etc on the same coffee table.  My experience, n=6, all six units ran neck and neck, within a particle or two, from 6mcg/m3 up to 200 mcg/m3.  For a typical homeowner, my data, the $60 unit is plenty accurate to let you know if you have a particle problem.


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## Poindexter (Dec 10, 2022)

New observation today.  I am trying to update an old family recipe for home canned mincemeat pie filling.  My pH meter runs best (most accurately) at 25 C.  While I was setting up I had a particle counter running on the kitchen counter 55 inches from the center of the skillet where I was cooking up a batch of oatmeal pancakes from Laurel's Kitchen - and fiddled with the wood stove settings looking for 25C ambient.

1. If you are making Laurel's oatmeal pancakes, separate your eggs.  Put the yolks in with the milk and oatmeal in one bowl.  Put the egg whites in a separate bowl and let them come up to room temp.  Beat the whites to stiff peaks and fold them gently into the rest of the batter without a lot of air loss so you end up with edible cakes instead of manhole covers.

2. PM2.5 exposure is inevitable for all of us.  Even though I saw 730 mcg/m3 close to the skillet while cooking, the meter out in the stove room only budged from 6 mcg/m3 to 15 mcg/m3 while I was cooking.  Within an hour PM2.5 counts in the kitchen were less than 50 mcg/m3 with poor air circulation.

3. My family mincemeat pie recipe is not quite but almost updated to modern food safety standards, after four previous generations of 'no one has died from eating this yet.'  I am focusing on the area near the "Praise His Name" finding, with an aggregate pH reading after making slurry over the FDA mandated #8 sieve in the (food safe)  vicinity of pH 3.8.

4. My goal is to open one pint of minced fruit, grill a ribeye around 18-20 ozs, dice the ribeye, then combine both of those in a pie shell with a half pint of dark sweet rum to make one mincemeat pie.  Home canning fatty meat like pork shoulder or beef rib roast is a bit of a challenge, but if I reverse sear the meat on the day I am making the pie there is no problem.  The grid is 5 variations of canned minced fruit v- 2 variations of skillet browned hamburger.  Wife Approval Factor re: the PHN variant is remarkably high.


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## Poindexter (Dec 19, 2022)

New problem this morning.  The wife woke up before her alarm went off to let me know she smelled some acrid burning something smell.  I have been spot checking my indoor particle counts knowing the single filter taped to the back of one fan was getting to be pretty dirty and would have to be replaced soon.

I saw all zeros on the main screen in the master bedroom early, but after 15 minutes or so I toggled the button for page two and did see some tinies.  I took the used filter off the one fan, and put the three filter Pbox into service, fan on low, and after about 5.5 hours I had made a dent in the tiny particles.  

My wood stove is running wide open ( I am off today) with the deck fans off.  I have reheated some leftovers but not cooked anything on the cook stove.


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## Poindexter (Dec 20, 2022)

My wife got home, could no longer smell "burnt acrid" and proceeded to saute some darn kale, but she at least used some canola oil for the saute, so the leftovers will scrape more easily into the trash can tomorrow morning.  Particle monitor is still in the master bedroom, diagonally opposite the kitchen in 1200 sqft.


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## Tonty (Dec 24, 2022)

I’ve been thinking some about this filtering air. It could be automated fairly easy, but it would fall out of the  qualifications  of “cheap.” I use HomeSeer for some home automation. I could get an Ambient Weather indoor or outdoor particulate monitor (I already have an Ambient weather station reporting to the cloud), sync with HomeSeer plugin, and run an IFTT protocol that would turn my furnace fan (through Ecobee thermostat synced with HomeSeer plugin) on and back off when particulate counter reached a predetermined setpoint. 
The same could be done with the box fan setup with it plugged into a Z-wave outlet or plug. 
But if a person doesn’t have any home automation setup already, it wouldn’t be worth it. It’s pretty easy to get up and turn a fan on. 😁
I doubt I’ll do it, but interesting scenario.


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## Poindexter (Dec 24, 2022)

@Tonty , if your average ambient outdoor air is good enough that might make sense.  


Fairbanks has some of the worst air quality in the USA, so I just run a 20 inch box fan on low year round unless the summer time wildfire smoke is particularly bad.


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## Tonty (Dec 24, 2022)

I don’t have the particulate monitor at this point, just this weather station. https://ambientweather.com/amws5000.html
I think our air quality is great most is the time, as we live in the country at least 40 minutes from any sizable town. Only time it gets bad is in the spring when the pastures are burned off, and then it could be pretty bad for short periods of time. I’ve considered getting the monitor just for curiosity sake, to check and see. 🤔
Take a look, I don’t know much about these. You think they are any good?
Indoor:
https://ambientweather.com/amwepmpmwiin.html
Outdoor:
https://ambientweather.com/ampm25.html


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