The choice of which filter to buy for your furnace depends on how much you want to spend and what you’re trying to accomplish.
Type of Filter – For most homeowners, a MERV 7 or 8 pleated filter provides a good balance between cost and furnace efficiency. But if you’re a clean freak or have family members with allergies or low-immunity issues, spending more on a high-efficiency (MERV 11 and higher) filter may be justified. Make sure you read your furnaces mfg documentation, there may be a specific MERV rating or max MERV Rating limitation.
High-efficiency filters capture 99 percent of airborne particles as small as 0.3 microns (bacteria and viruses, fumes and pollen). But you’ll have to run your furnace fan full time to get the maximum benefit from a high-efficiency filter, and that will cost more. Figure the extra cost into your decision.
Caution – A clogged filter can burn out the blower motor, damage the heat exchanger and cost you hundreds of dollars in wasted energy, your furnace may not even turn on with a dirty filter.
Buying a Filter – Traditionally, furnace filters were designed to protect the furnace and fans. With increased air quality awareness, some filters are now being installed to reduce exposure to particles which can affect your health. There is a wide variety of furnace filters available. However, you may find it confusing to select one which is suitable. CMHC has published a document, Furnace Filters, which can provide you guidance when selecting a filter.
When and How to Replace – Make sure you read the information on the furnace filters’ packaging. There is a specific way to replace the filter. The arrow should face the furnace. Most 1 inch thick filters should be replaced approx 2-3 months, others that are 4-5 inches are replaced every 6-12 months.