How do I improve indoor air quality in a Minnesota house in winter?
To improve indoor air in a Minnesota winter, fix moisture first, then filtration, then fresh air. Watch windows and a hygrometer, humidify only if the house is dry, use a 4- or 5-inch MERV 13 filter, ventilate tight houses and test for radon. Equipment runs $350–$2,800 installed with us.
Key points
- Start with an inexpensive hygrometer and your windows. Together they tell you whether the house is too dry or too wet.
- Too dry: add a whole-home humidifier with an outdoor-sensing control.
- Too wet or stale: more ventilation, usually an HRV or ERV in a tight house.
- A 4- or 5-inch MERV 13 media filter handles dust and dander without choking the blower.
- Skip ozone generators; EPA says they don't clean indoor air at safe levels.
Fix moisture first, then filtration, then fresh air, in that order. From November to April a Minnesota house is a sealed box, and the insulation and weatherstripping that cut the heating bill also hold dust, dander, cooking smells and moisture inside. Out of order, the fixes backfire: a humidifier in a house with wet windows, or a MERV 16 filter on a furnace already short of air, makes things worse.
How do you measure indoor air quality at home?
Buy an inexpensive hygrometer and put it in the main living area for a week, then move it to a bedroom. Many smart thermostats show indoor humidity too. While you're at it, look at three things:
- The windows. Water or frost on the inside of the glass means the house is holding more moisture than the windows can handle at that outdoor temperature.
- The dust. Gray film on dark furniture a day or two after cleaning points at filtration or leaky return ducts.
- Your nose. Cooking smells that hang around into the next day, musty closets on outside walls, or a stuffy bedroom in the morning mean the house isn't exchanging enough air.
What causes common winter air problems?
| What you notice | Likely cause | Fix | Who does it |
|---|---|---|---|
| Frost or water on the inside of windows | More moisture than the glass can handle | Humidifier down, bath and range fans on, more ventilation | You first, then a technician for an HRV or ERV |
| Static shocks, dry skin, gaps in the hardwood | Humidity too low | Whole-home humidifier with an outdoor-sensing control | HVAC technician |
| Dust film a day after cleaning | 1-inch filter, air slipping around it, leaky returns | Media filter cabinet, sealed return ducts | HVAC technician |
| Stuffy bedrooms in the morning | No fresh air in a tight house | Run the ventilator, open doors, fan on circulate | You, or a technician if there's no ventilator |
| Smoke smell on still nights | Wood smoke or wildfire smoke drifting in | Fan on continuous with a MERV 13 filter, a room HEPA unit | You |
| CO alarm sounding | Possible combustion or venting problem | Everyone outside, then 911 | Fire department, then a technician |
Is your house too dry or too wet?
Most Minnesota houses run dry in January: static shocks, cracked lips, gaps in the hardwood. The fix is a whole-home humidifier on the furnace, set to the range in the FAQ below. An outdoor-sensing control lowers the target on its own when a cold front arrives, which keeps the windows from frosting over on a -20°F morning. Our whole-home humidifier guide compares bypass, fan-powered and steam units, and our humidifier service covers installing and servicing them.
Tight houses often go the other way. Showers, cooking and a full household put a lot of water into the air, and with no leaks to let it out, the windows sweat. Adding humidity there is the wrong move. Turn the humidifier down or off, run the bath fan during and after showers, use a range hood that vents outside, and look at mechanical ventilation.
What furnace filter works best for dust, dander and smoke?
The 1-inch filter slot on most furnaces is a compromise. A cheap filter protects the blower and not much else. A 1-inch MERV 13 filter catches more but can choke the airflow. The better answer is a 4- or 5-inch media cabinet in the return, holding a MERV 13 filter with far more surface area. Our MERV rating guide shows what each rating catches, and our air purification service covers media cabinets, electronic cleaners and UV.
On nights when the neighborhood's fireplaces and wood stoves are going, or when wildfire smoke drifts in, running the furnace fan continuously sends more air through the filter. If dust keeps coming back no matter what filter you use, leaky return ducts may be pulling air from the basement or wall cavities around it.
Why do tight houses need mechanical ventilation?
Newer houses, and older ones that have been air-sealed, don't leak enough to air themselves out. That's why the Minnesota Residential Energy Code requires mechanical ventilation in homes built under it, sized by floor area and bedroom count. An HRV or ERV brings in outdoor air and exhausts stale air while recovering heat from the outgoing stream. Which one fits depends on whether your house runs wet or dry in winter, which our ERV vs HRV post walks through, and our ventilation service covers installing and balancing them.
If you already have one, make sure it's actually running. It's common to find ventilators switched off, with plugged filters, or with outside hoods buried in snow. Clear the hoods after every big snowfall, the same way you'd clear the furnace vents.
What about carbon monoxide and radon?
Two air problems you can't see or smell deserve a place on the list.
Carbon monoxide. Minnesota law requires a working CO alarm within 10 feet of every room used for sleeping. Check the dates on yours; our CO alarm placement guide covers where they go. After a heavy snow, check that high-efficiency furnace vents on the side of the house aren't drifted over; see clearing a frozen furnace vent.
Radon. The Minnesota Department of Health says more than two in five Minnesota homes have radon levels that pose a significant health risk, and recommends testing every home (MDH radon page). Radon comes from the soil, not the furnace, and mitigation is its own specialty. Winter, with the house closed up, is a sensible time to run a test.
When should you call a technician about indoor air quality?
Most of this list is yours to handle. Stop and call when you see:
- A CO alarm going off. Everyone goes outside first, and someone calls 911 from there. Nobody goes back in to open windows.
- Soot, scorch marks or a burning smell that doesn't fade around the furnace. Turn it off at the service switch and call.
- Windows that still sweat with the humidifier off. The house needs more ventilation, and the ventilator needs to be sized and balanced.
- Water around the furnace or humidifier, which usually means a plugged drain or a stuck water valve.
- A ventilator that won't run, or one whose filters and core haven't been cleaned in a year or more.
A dusty smell the first few minutes of the heating season is normal and fades.
Which air quality products should you skip?
- Ozone generators. They're sold as air purifiers. EPA says ozone at levels that don't exceed public health standards is generally ineffective at cleaning indoor air, and ozone irritates the airways.
- Big claims on small boxes. A plug-in unit that promises to clean a whole house doesn't. A portable HEPA unit sized for one room is fine for a bedroom.
- Add-ons before the basics. UV lights have a real but narrow job, keeping the AC coil clean, and they don't replace filtration.
What does indoor air quality equipment cost?
Our installed range for indoor air quality equipment is $350–$2,800, from a media filter cabinet at the low end to a steam humidifier or ventilator at the top, with a written flat-rate quote first. For context, national cost guides like HomeGuide put a typical whole-home humidifier at $400–$1,200 installed and a media cabinet at $400–$800, and a typical national range for an ERV or HRV tied into existing ductwork is $1,300–$2,500, per Fixr and Trane. If a furnace replacement is coming, add these then, since the return and supply plenums are being rebuilt anyway.
Filters, humidifier pads and ventilator cores can all be checked at a furnace tune-up, from $129. Our tune-up in Minneapolis page has the details, and you can ask us about a maintenance plan. If a humidifier, ventilator or furnace has stopped working, the $79 trip charge is waived when you approve the repair. Call 612-429-3465 to talk through which piece fits your house.
Common questions about air quality
What humidity should my house be in winter?
Roughly 25–35% in cold weather, and lower in deep cold. The colder the glass, the less moisture the house can hold before windows sweat or frost. Let the windows decide: if water or frost shows up on the inside of the glass, turn the humidity down. An outdoor-sensing humidifier control does this automatically.
Do plug-in air purifiers help?
A portable HEPA unit sized for the room helps in a bedroom or home office, especially for someone with allergies. It won't treat the whole house the way a ducted filter does. Avoid any unit that makes ozone on purpose; EPA says ozone generators shouldn't be used in occupied spaces and that ozone at safe levels does little to clean the air.
Should I test my house for radon?
Yes. The Minnesota Department of Health recommends that every Minnesota home be tested. Follow the kit instructions on placement and keep the house closed during the test; winter, with the house sealed up, is a sensible time. Radon mitigation is separate specialty work from heating and cooling, so a high result goes to a radon mitigation contractor.
Why does the house feel stuffy in the morning?
In a tight house, bedrooms with the doors closed build up moisture and stale air overnight, and nothing brings fresh air in. A ventilator running on its continuous setting fixes that. Without one, leaving bedroom doors open and running the furnace fan on low circulation helps spread what fresh air the house does get.
Sources
- Minnesota Department of Health health.state.mn.us
- U.S. Environmental Protection Agency epa.gov
- Minnesota Statutes 299F.51 (carbon monoxide alarms) revisor.mn.gov
- Fixr: ventilation installation costs fixr.com
- Trane: Is a whole-house ventilator right for my home? trane.com
- HomeGuide: humidifier costs homeguide.com