How often should you change your furnace filter in Minnesota?
Check a 1-inch furnace filter monthly in heating and cooling season and change it when dirty, or at least every three months, as ENERGY STAR advises. A 4- or 5-inch media filter usually lasts 6–12 months. A furnace or AC tune-up starts at $129.
Key points
- 1-inch filters: check monthly in heating and cooling season, change when dirty, and at least every 3 months (ENERGY STAR).
- 4- to 5-inch media filters last far longer; AprilAire rates its MERV 10–13 filters for a year, less if the fan runs all the time.
- Pets, drywall dust, wildfire smoke and a fan set to On load a filter faster.
- Buy by the nominal size on the old frame and point the airflow arrow toward the furnace.
- A higher MERV filter in a thin slot can choke airflow; that's a static pressure question, not just a filter question.
Check a 1-inch furnace filter every month and change it when it looks gray or fuzzy, and never let it go past 3 months; a 4- or 5-inch media filter usually lasts 6 to 12 months. The "every 90 days" on the package is a ceiling, not a schedule. Below: how to check one, what to buy, and how to tell a dirty filter from a furnace problem.
What do ENERGY STAR and the manufacturers recommend?
| Filter | Guidance | Source |
|---|---|---|
| Any filter | Inspect, clean or change once a month | ENERGY STAR maintenance checklist |
| 1-inch disposable | Check monthly, especially in winter and summer; change if dirty after a month; at minimum every 3 months | ENERGY STAR heating and cooling tips |
| Furnace factory filter | Clean (permanent) or replace (disposable) every two months or as required | Goodman installation instructions, single-stage furnaces |
| 4- to 5-inch media, MERV 10–13 | Change once a year; check every six months if the fan runs all the time | AprilAire filter FAQ |
| 4- to 5-inch media, MERV 16 or MERV 13 with carbon | Change every six months | AprilAire filter FAQ |
The EPA's page on MERV ratings adds the rule that sits over all of these: every filter needs periodic replacement, and you should follow the filter maker's recommendation. Goodman's installation instructions put the stakes bluntly, calling improper filter maintenance the most common cause of inadequate heating or cooling performance.
Why do furnace filters clog faster in Minnesota houses?
The heating season here stretches from October into May, and with central air the same blower and filter keep working through July and August. The filter gets a real break for only a few weeks each spring and fall.
Things that shorten the interval:
- Pets. Dog and cat hair mats on the face of a 1-inch filter fast. With a shedding dog, a monthly change in winter is normal.
- Remodeling. Sanding drywall can clog a filter within days. Swap it when the dust settles, and tape plastic over return grilles during the work.
- Wildfire smoke. The EPA's wildfire smoke guidance recommends a MERV 13 or higher filter during smoky periods and says to check it often and replace it when it looks dark brown or black. On a smoky summer, look weekly.
- Running the fan on "On." The EPA suggests switching the fan from Auto to On during smoke events so the filter cleans the air continuously. That helps, and it also means far more air goes through the filter. AprilAire says the same about its media filters: if the fan runs all the time, check it at six months.
- Older city houses. Many Minneapolis and Saint Paul furnaces sit on ductwork left from a gravity system conversion, often with too little return air. A slightly dirty filter starves those systems sooner than it would in a newer house.
A filter that goes black within a couple of weeks is loaded with something other than household dust, usually soot, and that needs its own diagnosis. Read why a furnace filter turns black.
How do you check a furnace filter?
- Turn the thermostat off or to a low setting so the blower isn't running while the filter is out.
- Slide it out and look at the entering side, the side facing away from the furnace. Gray or fuzzy with visible dust means change it.
- Hold it up to a light. If light barely comes through, it's done.
- Look at the slot. Dust piled on the blower side, or a filter bowed in the middle, means air has been leaking around it or it's overdue.
- Put the door or cover back firmly. On many furnaces the blower door presses a safety switch, and a loose door leaves the furnace off.
How do you find the right furnace filter size and direction?
- Size. Match the big numbers printed on the old frame, such as 16x25x1. Those are the nominal dimensions you shop by; the actual size listed beside them runs a fraction of an inch smaller.
- Depth. A 1-inch slot takes a 1-inch filter. A media cabinet takes the specific media made for it, which a hardware store may not stock, so buy a spare.
- Arrow. The airflow arrow points toward the furnace, in the direction air travels from the return duct into the blower.
- Fit. Gaps around the edges let air skip the filter completely. Goodman's instructions say a replacement must be the same type and size as the one it replaces.
- Date it. Write the install date on the frame with a marker. It settles the "when did we last change this" question.
What MERV rating should a furnace filter be?
A higher MERV number traps smaller particles and also pushes back harder on airflow, most of all in a thin 1-inch panel. The EPA recommends at least MERV 13, or "as high a rating as your system fan and filter slot can accommodate," and says you may need an HVAC technician to decide what yours can handle. Our post on the best MERV rating for allergies goes through that choice.
The number a technician uses to decide is static pressure, the resistance the blower pushes against. A dense or dirty filter raises it, which cuts airflow, can trip the furnace's high limit in winter and can freeze the AC coil in summer. Our explainer on static pressure covers how it's measured. If your system is already near its limit, the fix is a deeper media cabinet or more return air, not a denser thin filter.
And if you're tempted to run without one while you wait for the right size, read what happens when you run a furnace without a filter first.
What should a tune-up cover for the filter?
A maintenance visit is a good time to confirm the filter size, check for bypass around the edges and settle on a realistic change interval for your house. A furnace or AC tune-up is from $129, or $219 for both. If you're ready to stop buying 1-inch filters every month, our air purification service covers media cabinets, and static pressure should be measured before you pick one.
When should you call a technician about the furnace filter?
Call if the filter is dirty again within two weeks, turns black, or is sucked out of shape, or if the furnace keeps shutting off on the high limit even with a clean filter. Those point to a duct, blower or combustion problem, not a filter schedule. Book maintenance in Minneapolis or any other town we serve at 612-429-3465.
Common questions about maintenance
Does a Minnesota furnace really need a filter change in summer too?
If you have central air, yes. The AC coil usually sits right on top of the furnace and uses the same blower and filter, so the filter works from the first fall cold snap to the last humid week of summer. The only real break is a few weeks in spring and fall when neither is running, which is a good time to check it.
How do I know my filter is dirty if it's a dark color to begin with?
Compare it with a new one held beside it, or hold it up to a light. If light barely passes through, or dust is caked on the entering side, change it. AprilAire's guidance for its media filters is to replace them when the color goes from bright white to dark gray, and immediately if dirt starts to cake on the outside.
Is it bad to change the filter too often?
No, only more expensive. A new filter is always less restrictive than a used one. The bigger mistake is going the other way: stretching a 1-inch filter through a whole heating season, or buying a denser filter than the system can breathe through and then leaving it in longer because it cost more.
Can I wash and reuse my furnace filter?
Only if it's sold as a permanent, washable filter. Goodman's furnace instructions say filters should be cleaned if permanent or replaced if disposable, and replaced with the same type and size. Disposable pleated filters can't be washed; water ruins the media and can grow mold in the cabinet.
Sources
- ENERGY STAR energystar.gov
- U.S. Environmental Protection Agency epa.gov
- Goodman manufacturer documentation goodmanmfg.com