I was a HVAC service technician for over 11 years but now I am a stay-at-home Mom. I’m going to give a technical explanation and a non-technical explanation on what type of filters to use and how to figure it out.
A master technician that furthered my training in 2002 explained furnace filters to me. But, here is my disclaimer: this post is just a generic know-how and always rely on your qualified HVAC technician to give you knowledge and do repairs on your own personal heating equipment. Each home is different and each installation is different making the technician physically working on your equipment the one who will know best!
What is your furnace filter for?
The only job of a furnace filter is to protect your HVAC equipment from chunks of debris. If you get debris collecting in your equipment it can cause many problems such as:
- blower motor failure
- premature cracking of the heat exchanger
- safety failures
- freeze up of the evaporator
- no air conditioning / heating
- additional consumption of energy to heat and cool your home
Being diligent about changing your filter is key to the safety, longevity and efficiency of your equipment. Using the proper filter and proper size filter for your equipment is also important.
Many manufacturers market their filters so that you believe that a filter is meant for your respiratory health, helping with dust mites and allergens. I don’t doubt that those filters can do that. Remember though, filters are designed for the protection of your equipment only. If you have indoor air quality issues or certain respiratory health issues there is special equipment one can purchase to help with those issues.
What kinds of disposable filters are there?
There are many on the market. There are the inexpensive blue/white fiberglass filters all the way up to disposable accordion style filters that cost around $50 each. Some of the low-fold accordion style filters restrict too much air flow because of not having enough surface area for the air to be pushed through. Some of the accordion filters have a lot of folds giving plenty of surface area for air movement but those seem to be the costly filters that still need to be checked/changed every 30 days.
Which one should I use?
My question for you is: how bad do you want to know that answer? If your answer is badly, then there are some tests that your qualified HVAC technician can do in your home to tell you.
Your technician can take some simple air flow readings using a manometer. I used a manometer to measure air pressure in duct work, gas pressure in gas piping, and it can also tell me the difference in pressure between two places in your duct work.
Since air flow is one of the biggest parts of your heating and air conditioning equipment functioning properly, I used mine often. (air flow, air flow, air flow!!!)
Here is my cheat sheet that I used for 11 years. It stayed with me in my tool box and was at my fingertips when I needed it. And yes, there are people with high efficiency DC blower motors on their equipment, and yes they can ramp up and sort of compensate for dirty or restrictive filters, but why make your equipment work that hard especially when you bought it with efficiency in mind!
Your technician can take air flow at letter A and letter B, and if they aren’t in the parameters stated on the cheat sheet it’s time to look at what the problem is.
If you really want to go the extra mile, buy 3 different kinds of filters and take readings with each one of them at a time in the filter slot. Also think about having a layer of dirt on them. If a clean filter is on the border of not being in the parameters, then most likely it being dirty will make it out of specs. Meaning if the air pressure readings with the clean filter are close to being not in the parameters of what the ideal readings should be on the cheat sheet, then most likely with that filter being dirty or slightly dirty, it will make it not in the parameters.
Your technician can check to make sure your blower speed is set correctly and duct work is not over or undersized.
Still not satisfied with that answer?
Bringing it home
Okay, so let me get out of tech talk.
I live in the country, windows are open, clothes flapping out on the line drying, dog and two active boys are running in and out of the house. My filter is changed 2 times a month and I buy the cheapest fiberglass filter I can find.
We have a lot of dirt. Plain and simple. I also do a tune-up and cleaning once a year – not only for cleanliness – but for safety. You should too, but call for a qualified technician.
I know that the cheap fiberglass filter will allow enough air flow, catch the clogging chunks, won’t make me broke, and a cleaning every year will take care of the pesky fine particles.
Since we don’t suffer from allergies, there is no need to have any extra filtration equipment.
A friend of mine lives in the suburbs and has no kids, no animals, lives by himself, doesn’t open windows and has low use of equipment (part of the year he is gone on business). He uses an accordion style filter with a lot of folds and only changes it 2 times a year! It works perfectly for him. He also gets a tune up / cleaning every year, not so much because of dirt, but for safety.
I found that the low-fold accordion filters tended to be restrictive, even being brand new right out of the wrapper. I am sure there are a lot of neigh sayers but the manometer doesn’t lie.
So whatever you decide to take from this post is up to you but these points should be emphasized:
- Change/check whatever filter you choose often, at least every 30 days.
- Always have a qualified HVAC Technician to work on, repair and install your equipment.
- For safety sake get a tune up / cleaning every year.
What kind of filters do you use in your furnace?
Find furnace filters at Amazon
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