How That High-efficiency Filter Is Ruining Your Furnace & Your Air Quality.
Updated: Jan 14
With the colder weather many of us are replacing our furnace filters. And of course we want the high efficiency small particulate filter, after all a better filter is better for the furnace and air quality right? Well It might surprise you to hear that it is not good for your furnace or indoor air quality.
The Furnace Doesn't Move Enough Air To Clean It
The purpose of a furnace fan is to gently deliver Just enough warm or cool air to the rooms where it is needed then stop, all the while using the least amount of energy to do it. So it does not turn over much air in fact far less than would be required to remove an adequate amount of air particulate matter (PM) from the air.
Furnaces Are Not Designed To Work With Small Particulate Filters
The purpose of an air filter in a furnace has nothing to do with the air you breathe. Its purpose is to protect internal components like the heat exchanger from damage caused by large particulate Matter (PM) in the air. Furnaces are designed to use a MERV 4 - 12 and would need special modifications to handle anything higher. Using a filter with a higher MERV rating than recommended by the manufacturer will lead to performance issues and can cause damage to the furnace and air conditioning components.
Clogged Filters & Filter Bypass
High MERV rated filters will clog sooner than lower ones. Once this happens the air flow through the furnace is impeded which could lead to the heat exchanger to overheat and crack or your AC evaporator coils to freeze or cause excessive condensation which can rust the furnace. Sometimes when the filter is clogged the increase in pressure can fold the filter and allow air to bypass or blow right past the clogged side of the filter and carry debris into the furnace and then your breathing air!!
Ok so now we know that asking your furnace to filter your breathing air is kind of like trying to use your toaster to cook a turkey… Not a good idea. So go forth and buy many cheap furnace filters and change them often. It will be better for your breathing air and your furnace.
How Then Do I Improve Indoor Air Quality?
Air filtration systems are designed to move a large volume of air continuously through a small particulate matter (PM) filter (typically MERV 15 or higher). There are small room units as well as whole house filtration systems available. These are purpose built systems that do a far better and more efficient job filtering the air than a furnace could ever hope to.