Change your furnace filter by switching off the furnace, sliding out the old filter, and fitting a new one of the same size with its airflow arrow pointing toward the furnace. Do it before the heating season starts, because a clogged filter makes the system work harder and can lead to overheating.
Across most of Canada, furnaces move from occasional use to daily work in October. A dirty filter restricts airflow, and Service Experts, a major Canadian heating and cooling company, warns that neglecting replacements risks furnace overheating, short cycling and eventual system failure. ENERGY STAR advises homeowners to check the filter monthly and replace it at least every three months. Standard filters are often swapped every one to two months, and as often as every 20 to 45 days in homes with several pets or an allergy sufferer, according to Service Experts’ guidance for Canadian homeowners.
The job takes about five minutes and needs no tools in most homes. It covers only the filter. Anything involving gas lines, wiring or the furnace’s internal parts is work for a licensed technician.
- Find the furnace and the filter slot. Most furnaces sit in a utility closet or the basement, with crawl spaces and attics as other possibilities. The filter is usually in the blower compartment behind a metal door on the lower half of the unit, or in a sliding slot beside the air handler.
- Turn off the furnace. Switch off the power to the furnace before you open the compartment. Many units have a service switch on or near the furnace. If you cannot find it, set the thermostat to off and wait for the blower to stop.
- Check the size. The dimensions are printed on the edge of the old filter, for example 16 by 25 by 1 inches. Buy a replacement with exactly the same size, since a loose filter lets dust bypass it.
- Pull out the old filter slowly. Slide it out gently so you do not damage or knock the housing out of place. Note which way the arrow on its frame points.
- Pick the right rating. Filters are graded by MERV (Minimum Efficiency Reporting Value). A higher number traps smaller particles, but filters above about MERV 13 are typically designed for hospitals rather than homes, according to Service Experts. If you are unsure what your furnace can handle, check the manual or ask a technician.
- Install the new filter. Look for the arrow on the new filter’s frame. It should point toward the furnace and the blower, in the direction the air flows. Slide the filter in until it sits flat with no gaps.
- Close the compartment and restore power. Make sure the door is fully latched, since many furnaces will not run if it is open. Turn the power back on and set the thermostat.
- Mark your calendar. Write the date on the filter’s edge or set a phone reminder so you check it monthly and replace it on schedule.
If the filter slot is hard to reach, the furnace makes unusual noises, or you smell gas, stop and call a licensed heating technician. A yearly professional inspection before winter is also a good idea, and it is required by some warranties.
Sources: Service Experts (Enercare), “How to Find Your Furnace and Change Your Furnace Filter”; ENERGY STAR guidance on filter replacement frequency.
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