What size furnace filter do I need? Read the frame
Your filter size is printed on the edge of the filter you already have: three numbers like 16x25x1, width by height by thickness in inches. Pull the old one out, read the frame, and buy that size. The arrow on the frame points toward the furnace.
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From one of our jobs
Three 16x25x1 filters, size on the frame
Right now: Read the size printed on the frame of the filter in your furnace, and buy two so a spare is waiting.
Those numbers are the nominal size, rounded up, so a 16x25x1 filter actually measures a little smaller. That’s on purpose so it slides in. If the old filter is missing or the label is worn off, measure the slot and round up to the nearest inch.
One inch filters are the most common and the ones that clog fastest. Change them every one to three months, more often with pets. If yours is gray and bowed when you pull it, it’s overdue.
Quick answers
What people ask about furnace filters
How do I find my furnace filter size?
Read the frame of the filter that’s in there now. It’s printed on the edge as width x height x thickness, like 16x25x1.
Which way does the arrow on a furnace filter go?
Toward the furnace, in the direction the air moves. On most units that’s toward the blower.
How often should I change my furnace filter?
One inch filters every one to three months. Thicker media filters, four or five inches, last six months to a year.
What MERV rating should my furnace filter be?
MERV 8 to 11 suits most homes. Higher catches more but can choke a system that wasn’t built for it.
Who do I call for furnace service in Northern Virginia?
Call SwiftPro at (703) 997-9757. We check furnaces across Northern Virginia, filter included.
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SwiftPro Heating, Cooling & Plumbing
4230 Lafayette Center Dr N, Chantilly, VA 20151
44679 Endicott Dr, Suite 211, Ashburn, VA 20147
SwiftPro Plumber & Water Heaters
4200 Lafayette Center Dr, Suite N, Chantilly, VA 20151
Virginia Class A contractor license #2705192276