In Minnesota, change a 1-inch furnace filter every one to two months during heating season, and a 4- to 5-inch media filter every six to twelve months. Thin fiberglass filters need replacing every 30 days. Because our heating season runs October through April, most Twin Cities homes go through four to six 1-inch filters per winter — more with pets, allergies, or an ongoing remodel.
Replacement Schedule at a Glance
- 1″ fiberglass — replace every 30 days. Protects the equipment, not your air.
- 1″ pleated (MERV 8–11) — replace every 1–2 months in season. The most common residential filter. Check monthly.
- 2″ pleated — replace every 2–3 months. More surface area, longer life.
- 4″–5″ media cabinet — replace every 6–12 months. Still worth a look at mid-season.
- Washable — replace every Wash monthly. Must be fully dry before reinstalling.
Why Minnesota Is a Different Case
National advice usually says every 90 days. That number is written for a climate where the furnace runs a few months a year. Here it runs for seven. A furnace in Burnsville or St. Paul logs far more hours between October and April than the same unit would in a milder state, and every one of those hours pulls air through the filter.
Our homes are also sealed tight. That’s what makes a Minnesota winter affordable, but it means the same indoor air recirculates through the same filter again and again. Add a whole-home humidifier and there’s mineral content in the airstream too. Check your filter monthly from October through April, and change it when it’s dirty rather than when the calendar says so.
How to Tell a Filter Is Due
- Hold it up to a light. If light doesn’t pass through the pleats, replace it.
- Look for gray, matted buildup on the intake side — a light dusting is fine, a felt-like layer is not.
- Watch run times. A furnace running longer to hit the same temperature is often fighting restricted airflow.
- Note any short cycling. A furnace that fires for two or three minutes and quits is frequently overheating behind a clogged filter.
What MERV Rating Should You Use?
MERV measures how fine a particle the filter captures. Higher isn’t automatically better, because a denser filter also restricts airflow.
- MERV 1–4: equipment protection only. Fine if you change it religiously.
- MERV 8–11: the sweet spot for most Twin Cities homes. Catches dust, pollen, dander, and mold spores without straining the blower.
- MERV 13+: good for allergy and asthma households, but only if your system is rated for it. On an older furnace with undersized return ductwork, a MERV 13 one-inch filter can restrict airflow enough to overheat the heat exchanger.
If you want serious filtration, a 4- or 5-inch media cabinet usually beats a high-MERV one-inch filter — more surface area means better capture and less pressure drop at once.
What Happens If You Skip It
A neglected filter is behind a large share of the service calls we run in January. Restricted airflow makes the heat exchanger run hot, which trips the high-limit switch and shuts the burners down. The house never quite warms up, and the repeated thermal stress shortens the life of the heat exchanger — the single most expensive component in the furnace. A filter costs a few dollars. A heat exchanger does not.
How to Change It Correctly
- Turn the furnace off at the thermostat and note the size printed on the old filter’s frame, such as 16x25x1.
- Point the airflow arrow on the new filter toward the furnace, in the direction air travels from the return duct.
- Close the panel, turn the system back on, and write the date on the filter frame in marker.
Filter changes are part of every furnace maintenance visit we run, and we’ll tell you the right size, MERV, and interval for your system. Home Care Heating and Air serves Burnsville, St. Paul, Hopkins, Northfield and the surrounding Twin Cities metro. Call (952) 377-8774 or schedule at CallHomeCare.com/schedule.
Frequently Asked Questions
How often should I change my furnace filter in Minnesota?
Change a 1-inch pleated filter every one to two months during the October-through-April heating season, and a 4- to 5-inch media filter every six to twelve months. Check any filter monthly in winter, because Minnesota furnaces run far more hours than the national 90-day guideline assumes.
How many furnace filters will I use in a Minnesota winter?
Most Twin Cities homes go through four to six 1-inch filters across a heating season. Homes with pets, more occupants, or ongoing construction go through more.
What MERV rating is best for a furnace filter?
MERV 8 to 11 is the best balance for most residential systems. It captures dust, pollen, and pet dander without restricting airflow. MERV 13 and above filters more finely but should only be used if your furnace and ductwork are rated for the added pressure drop.
Which way does the arrow on a furnace filter point?
The arrow points toward the furnace, in the direction air flows — away from the return duct and into the blower. Installing it backward reduces filtration and increases resistance.
