Homemade air filters - Good indoor air quality, cheap

[Poindexter]

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.

 

[EbS-P]

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.

 

[Poindexter]

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.

 

[Poindexter]

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.

 

[Poindexter]

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.

 

[begreen]

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

 

[Poindexter]

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.

 

[Poindexter]

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:

 

[Poindexter]

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.

 

[EbS-P]

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.

 

[Poindexter]

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.

 

[EbS-P]

Trying to attach the pdf

 

[Poindexter]

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.

 

[Rusty18]

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.

 

[begreen]

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.

 

[Poindexter]

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.

 

[Poindexter]

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.

 

[Poindexter]

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.

 

[Poindexter]

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.

 

[Tonty]

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.

 

[Poindexter]

@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.

 

[Tonty]

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

 

[Poindexter]

Does anyone have a youtube login? I don't have one. It might be worth creating one to tag this Brit into this thread:

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He has one of those tiny UK woodburners we get threads about a couple times every winter, and a particle counter.

I have no idea how the UK version of the USEPA converts raw particle counts to Air Quality Index. The most recent guidelines immediately to hand are on page 4 of this .pdf:

https://www.epa.gov/sites/default/files/2016-04/documents/2012_aqi_factsheet.pdf

When you can see a raw particle count of PM2.5 at 30 mcg/m3 returns an AQI (in the US) near the top of the moderate range, well on the way to unhealthy for sensitive groups.

I am going to get a user ID on youtube, this is probably a handy fellow to know.

 

[Poindexter]

Done and dusted. Perhaps he will stop by.

 

[Poindexter]

I have taken opportunity to dig around a bit for AQ in Norwich, England. It does seem the UK air police reference often the WHO guidelines for AQ: https://epha.org/the-who-air-qualit..., the WHO now,uniform targets for air quality.

Preliminary findings are that rag 'n' bone brown must have some sort of whole home filtration, as his IAQ (Indoor Air Quality) measurements are somewhat better than typical outdoor AQ measurements for Norwich, England. Norwich, Vermont of course is the home of MBT strategy for the free world, apropos of nothing at all on this website.

Given his 17k btu/hr (5kwh) max output burner, I suspect he (rag 'n' bone brown) has an existing whole house filtration system. I suspect he could have dramatically improved Indoor air quality with a single MERV 13 furnace filter duct taped to the intake side of a 20 inch box fan.

My fundamental questions for rag 'n`1