Why does your Heating & Air Conditioning guy worry so much about your furnace’s air filter?

There’s a lot of different things we can talk about in furnace filters. We can talk about the MERV rating, the brands, types, etc. However, today I’m going to talk about the simple things you should know about your furnace filter.  First, did you know that probably 95% of all the compressors in Air Conditioners and Heat Pumps that go bad can be attributed to dirty, clogged furnace filters. I’m not talking about a little dirty, I’m talking about the really clogged up filters that your furnace can’t breathe thru. An AC system needs the warm air in the house to pass over the indoor coil so it can pull the heat out of that air in order to properly function. If the filter is clogged up, then the air is moving to slow and it can’t pull the heat out and it causes a condition that we call “slugging”. This can cause the valves in your compressor to be damaged beyond repair and you could be  facing a very expensive repair bill. You think,” My air conditioner or heat pump is not that old. It will be OK”. Sorry folks, but the age has nothing to do with it when the filters cause it to go bad.  “Keep your filters clean.” It reminds me of something that happened to me last fall. I started my riding lawn mower up to cut the grass. It did not exactly work properly, but I kept it running and the engine threw a rod.  I checked my oil levels and they were extremely low. I had an extremely good mower, but my lack of maintenance cost me money that I would not have spent, had I just checked my oil. The same holds true for your furnace filters and your heating and cooling system. Change your filters when they start getting dirty and don’t wait for them to become clogged up with dirt.

Second, the type of filters does matter. The purpose of the filter is remove the dust from the air in the house and to keep the dirt out of the indoor “A-coil” or evaporator coil, as we know it in our trade.  The indoor coil is actually where our cooling takes place and it removes the humidity in the air as it cools. Well, this humidity that is removed is actually water vapor that is condensed to cold water on the coil. It runs thru hundreds of aluminum fins on the coil. It travels from the top to the bottom of the coil and runs on out the drain. As the condensation (water) runs down the coil, if the furnace filter is dirty and clogged, then the condensation will begin to freeze. This blocks the coil even more , so then it begins to freeze even faster. Soon, your coil will look like a 4-7″ thick block of ice and no air passes thru it and guess what,” You have NO Air Conditioning“.  Another thing that happens is if your filters are clogged, or you use the very cheap spun fibreglass filters, then there will be small dust and other particles that travel thru the coil. But, when the dust and other particles come into contact with the condensation, they will immediately start to attach themselves to the face of the coil. Eventually, they build up so much that the dust and dirt are catching the other dust and dirt and trapping it on the coil face and its also starting to pull the debris into the openings between the aluminum fins and again, the coils start to freeze up. Then, once again you have” NO air conditioning“. I have noticed down thru the years that the best inexpensive filter that you can buy is the cheapest pleated filter that you can find. Now, others might disagree with us, but this is from 30 years of observing this in the field and this is my opinion. Remember, everyone has different opinions about different things.  I believe that the cheapest pleated filter is able to pull out all the major dirt and it also allows the air to move freely thru it. However,  when you buy the more expensive pleated filters, then their composition is so dense, its like putting a clogged up filter in the system to begin with. Don’t be influenced by all the claims on the more expensive filters. They make a lot of claims, and yes, for the most part, they are true on what they say. It’s what they don’t tell you that causes the problems. If you have allergies and asthma, I think you will find that the cheap pleated filters do just as well and maybe even better for you than the more expensive ones do.  If you still have an old electrostatic filter from years ago (they look like they have monofilament fishing line as the surface), then discard it and get the cheap pleated filters. They work much better.  There’s also a lot of very good pleated filters out there that you only change once every 6 months to a year. I call them the “Lazy man’s filter”. They do an exceptionally good job. I like the Aprilaire brand the best, but Honeywell, General and some others have very good filters also. They are normally 3″-5″ thick and go into a special filter cabinet. You can also get a prescription from your doctor if you have allergies, asthma or some other breathing problems and then their installation is tax-deductible.  There is also the electronic air cleaner. Get rid of them and install a media filter in their cabinet. It will work much better. The very best filter that I’ve ever seen on the market is the “Aprilaire 5000 electronic filter”. It’s totally different from all the other electronic filters on the market and it incorporates a media filter also. The most expensive and what should be the best is the HEPA filter. It would be, except that it only filters about 10-20% of the air going thru the furnace at a time. I find this to be totally unacceptable and we will never install one unless they change to 100% filtration.

Remember, these are mostly opinions that I have from 30 years of observing heating and cooling equipment.  I won’t claim that I’m 100% correct on my observations, but the results that I’ve seen will not prove me wrong either.

Another thing to remember, if you put your dirty dishes in the dishwasher and do not turn it on, your dishes will never get clean.  Using the same principle, if you do not turn your furnace’s fan on at the thermostat, then the air  in your home will never get cleaned by the filter. Let the fan run and help reduce the air-borne dust in your home.