Furnace Filters

There’s a lot of misinformation out there regarding 1” wide disposable furnace filters, which effectively double as AC filters, as most residential AC systems, excluding condos, use the furnace’s air circulating fan to supply cool air to the home, and to draw warm air from the home back to the indoor portion of the AC to be removed, and most of that misinformation is perpetuated by the furnace filter manufacturing industry.  While the filter manufactures’ advertising is geared towards making you believe that a higher quality filter is better for your; furnace/AC, your home, and your family, this is not the case.  Using high-quality, high efficiency and highly effective furnace filters will expedite the degradation of your furnaced and AC, will be the cause of more frequent furnace and AC breakdowns leaving you without any heating and/or cooling until it’s repaired, not to mention the cost of the repair.

It’s a common misconception, perpetuated by the filter manufacturing industry, that the furnace filter is there to filter the air to provide improved air quality for the occupants, but such is not the case.  Rather, it’s there to act as a protective screen for the furnace, stopping anything too big to pass through the furnace without damaging it from being able to enter the furnace in the first place, and when we use a high quality furnace filter, we reduce the air flow thorough the furnace resulting in higher operating temperatures and increase the pressure the air circulating fan motor is working against, both of which expedite the degradation of furnace components.  On the AC side it’s worse, with high quality furnace filters restricting the air flow to the point that the AC system isn’t receiving sufficient heat from the house causing the AC system to freeze up. This freeze AC freeze up leaves the home with no appreciable cooling whatsoever, a very loud AC that seems to want to run almost endlessly, often causes the indoor portion of the AC system to be compromised by hydraulic force, as the water that’s freezing on that part of the AC system expands by 17% as it turns from liquid to solid, forcing anything in its path out of the way, often the copper and/or aluminum that indoor AC component is made of, causing a refrigerant leak), and when that frozen component eventually thaws out, much of that melt water drains down into the furnace, expediting the degradation of furnace components, and sometimes compromising them instantly.

If your furnace uses a 1” wide filter, then the cheapest furnace filter you can find is what your furnace and AC would prefer you use.  Note that we don’t mean “cheapest because you bought 100 of them from Costco”, but cheapest in the context of how much air they let through. An easy gauge for determining how much air a filter will let through is to hold the filter up to a light, to see how much light is coming through; the amount of light coming through will be the amount of air moving through it when it is in use.  What your furnace and AC would prefer, if your furnace is set up to use a 1” wide filter, is a filter that looks like it wouldn’t stop much more than leaves and plastic wrappers.

Note that most 1” wide washable/reusable furnace filters and electrostatic furnace filters (basically a powered 1” wide filter, not an electronic air cleaner (which can be used in place of a filter, and is effectively a bug zapper for dust)) are quite restrictive, and we recommend not using them for the same reason we recommend not using high quality disposable 1” wide furnace filters.

Now that said, the above-noted advice is only applicable to 1” wide furnace filters, what most Calgary area homes are set up for, and the wider a filter you use, the more restrictive, and thus better at filtering the air for the occupants, it can be without harming the furnace.  If the existing rack/holder for your furnace filters is designed for 1” filters, that rack can be replaced with one that’s designed to accommodate far wider filters, permitting the use of extra-wide filters that can do a good job of filtering the air for improved air quality without expediting furnace degradation.