Indoor Air Filtration the Saga
We have been rethinking our indoor air filtration for a month or more. The first thing that set us to thinking about it was the air filtration situation in our HVAC air handler. The situation was this: Jewel Plumbing & HVAC set up our HVAC and filter system, per our requirements. They built a 25"x 25" by 1" filter jig ahead of the squirrel cage fan compartment in the HVAC air handler. Our furnace is a LP gas fired forced air system with air conditioning. We had been sourcing our air filters for the first year from Jewel our installers, because it turns out that 25" x 25" air filters have not been all that common. For the first year we never saw any air filters of that size in the local box stores. Just recently we have seen a few start to appear. The filters we sourced from Jewel, were of the cardboard frame variety with very wispy synthetic fibers only 1" thick. They are the most rudimentary of HVAC air filters. After a year in the new house, we started to notice plenty of fine dust in the filter jig and even getting past the filter and all in the squirrel cage fan compartment. This is the situation set us to thinking about a different approach to home air filters.
We have tried many different air filter systems over our lifetimes from none to the most complicated electronic variety and just about everything in-between. As fate would have it, our neighbor Greg listed some 25" x 25" x 2" pleated paper air filters for free on Facebook Marketplace. Greg said they were free, because his supplier, Airfilters.com had sent the wrong size and he had no use for them. As with just about everything, air filters seem to have become much more sophisticated. We had never used a pleated paper airfilter in an HVAC, but we knew they are a bit "tighter" than the wispy nylon fibers, so we thought this will be better. We picked up the filters from Greg and then immediately discovered our HVAC air-handler would only allow a 1" thick filter to set in the filter jig. Shortly after we started to learn about the pleated paper filter ratings of MERV, FPR, and MPR.
MERV (Minimum Efficiency Reporting Value)
Scale: 1-16, with higher ratings indicating better filtration capabilities for a broader range of particles, from dust to bacteria.
FPR (Filter Performance Rating)
Scale: 4-10, aligning closely with the MERV scale but tailored for Home Depot’s retail environment.
MPR (Microparticle Performance Rating)
Scale: 300-2800, specifically measuring filtration efficiency for particles smaller than 1 micron
What all this meant to us is the higher the filtering capability the more air restriction, or load is placed the HVAC fan motor, and that is not great for the HVAC motor system. At this point we thought that we couldn't use the filters that Greg kindly gave us, but that's not the end of the story.
After a bit more research we settled on the idea of purchasing two 25" x 25" x 1" electrostatic HVAC air filters. We had used electrostatic filters previously with good results. They are a bit more expensive at $50-$100 for one filter. The good things about the electrostatic filters is that they are washable and reusable and may last for your lifetime, so you won't have to buy filters again. The other good thing is that they do filter dust well based on a static electric charge building up on the nylon mesh when air passes through AND they have a low air resistance that doesn't load the fan motor down. We purchased two electrostatic air filters at 25" x 25" x 1". We found our 25" x 25" x 1" for under $70 a piece. The reason that we purchased two was for ease and speed of replacing filters. Since the electrostatic must be washed then re-used, we thought we could always have a clean one ready so the filter swap would be just a quick remove and replace. With one, we would have to remove, wash, and wait for it to be dry before it should be reinstalled. This way we can wash the filter later at our leisure. We just place the dirty filter in the tub or shower and use the hand held shower head with hot water to back wash dust out of the filter. Below is a picture of an example of an electrostatic HVAC air filter, similar to what we purchased.
We thought great, but it would still be nice to filter out more dust and pollution especially here in the great cold north where we do spend a good bit of time inside during the winter. We looked around and found all sorts of great looking stand alone air filters. We settled on this one below.
Most all of these home air filters advertise HEPA filtration, and that is a very tight filter. After a little more research we discovered that the primary factor in filtering the air inside a home is the number of times you run the air volume of your house through the filter. With all of the HEPA filters they are very slow and low at moving the house air through the filter because they are such restrictive filters, and they also clog very quickly making the effectiveness even lower. That seemed no good, so we searched a bit more and learned more about the HEPA air filters, what we found was surprising. That is when we learned of the Corsi-Rosenthal Box air filters. It turns out that by just taping a pleated paper air filter, like those we obtained from Greg, to the front of a box fan, that is many times more effective than any of the neat looking HEPA home air filters! The YouTube video below tested five air filter brands, including the Levoit we were considering, with a Toronto University Air Quality Engineer. After listening, we ruled out the Levoit cool looking little HEPA air filter.
https://youtu.be/0uZKBlwLEFs?si=8HEXQqIkF9jSCzBa
Because we were convinced by the data in the video above and by the nerdy data in the next video below, we decided to build a Corsi-Rosenthal air filter system in the pattern of the video below. We went with the fan suggested, but were surprised by the cost! The fan was $170. We have never paid so much for a fan, but believe me when I tell you this is a NICE fan! The fan is actually designed and sold for indoor plant growing. Haha I wonder what that might be?? Well, we are just using it to filter our indoor air, promise. Below is the video that this wonderfully nerdy guy figured out. We think he is great. He did all the research and work and shared it with us so we could just benefit right away at a high level with very little effort. He performed a lot of research on the recommended fan type, considering air flow (a key) and noise level that becomes significant quickly. Who wants to listen to a loud fan? Not us.
https://youtu.be/KxPk8yOH-z4?si=QO7hUgnu_vmQwFJY
Using Greg's donated filters, this is what our beta test filter came out looking like.
This prototype filter seems to working great, but it is too big. We have obtained some 16" x 20" x 2" MERV 8 filters that will make the filter much less size obtrusive. We are thinking that the 16" x 20" x 2" filters will be our final configuration along with the Electrostatic filters in the HVAC air-handler.
Below are a few pictures of the cleaning of the HVAC air handler and changing the filter to the new electrostatic filter. First picture is our HVAC air handler installed in our crawlspace. The air filter access door is open at the left within the silver plenum.
Comments
Post a Comment