Homemade air filters - Good indoor air quality, cheap

[Poindexter]

@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.

 

[woodgeek]

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.

 

[semipro]

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

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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.

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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.

 

[Poindexter]

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.

 

[semipro]

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.

 

[Rusty18]

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.

 

[ben94122]

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

 

[semipro]

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 (broken link removed).

An explanation of MERV from Grainger here.

(broken image removed)

 

[sloeffle]

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.

 

[Rusty18]

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

 

[begreen]

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.

 

[EbS-P]

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.

 

[Brian26]

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.

 

[Rusty18]

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.

 

[semipro]

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.

 

[ABMax24]

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.

 

[Brian26]

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.

 

[EbS-P]

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.

 

[begreen]

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.

 

[EbS-P]

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

 

[peakbagger]

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.

 

[EbS-P]

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.

 

[SpaceBus]

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

 

[semipro]

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.

 

[SpaceBus]

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.