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Universal Air Systems

How-to · 5 minutes · easy

How to Change Your Furnace Filter

Replacing the air filter is the single most important DIY HVAC task. A clogged filter restricts return airflow, causes the heat exchanger to overheat, and is the #1 cause of mid-winter furnace lockouts. Costs $15–$40 for a quality filter and 5 minutes.

What you'll need

  • Garbage bag
  • New filter (matching size on the old filter's label)
  • Permanent marker

Steps

  1. 1

    Locate the filter slot

    Most filters slide into a slot on the side of the furnace cabinet, near the return-air duct. In some homes, the filter sits in a slot in the return ductwork upstream of the furnace itself.

  2. 2

    Note the airflow direction

    There's an arrow printed on the side of the existing filter pointing toward the furnace. The new one goes in the same orientation.

  3. 3

    Slide the old filter out

    Have a garbage bag ready — they get dusty. Slide straight out with light hand pressure.

  4. 4

    Slide the new filter in

    Same orientation as the old one — arrow pointing toward the furnace. The filter should sit fully in the slot, no gaps.

  5. 5

    Mark the next change date

    Write the install date on the filter edge with a marker. Recommended intervals: MERV 8 every 2-3 months; MERV 11 every 3 months; MERV 13 every 2 months.

When to stop and call

If you can't find the filter slot, the unit looks unfamiliar, or you've changed it but airflow still feels weak, send us a photo. (416) 258-2460.

Open 24/7

Stuck on a step? Send us a photo.

Most GTA calls get same-day service. Call, text, or request a fixed quote — we'll come back with a real ETA.

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Mississauga, ON · Greater Toronto Area and up to 2 hours out — London, Kitchener, Barrie, Kingston, Niagara.

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