Why Your House Feels Stuffy in Winter, and How to Clear the Air

Come January, the sun gets low enough to shine straight across the living room in the afternoon, and you can see what you're breathing. Dust hanging in the light. The house smells a little like last night's dinner and a little like the dog. Nobody's opened a window since Halloween.

That's a normal Michigan winter house, and most of it can be fixed. Some of it costs you a filter. Some of it takes equipment, and some of what gets sold for winter air quality doesn't do much of anything.

Why the Air Gets Worse in Winter

In summer a house breathes. Windows open, doors stay open, the air conditioner pulls moisture out, and the screen door slams forty times a day. Air turns over whether you plan for it or not.

In winter all of that stops. We seal the house up because heat is expensive, and that's the right call for the gas bill. But everything the house makes now has nowhere to go:

• Cooking. Searing, frying, anything on a gas range. The smoke and grease particles hang around for hours if the range hood vents to nowhere, and a lot of them do. Plenty of over-the-range microwaves just blow the air back into the kitchen.
• Pets. Dander builds up faster when the dog's inside eighteen hours a day instead of eight.
• Showers and laundry. Moisture. In a tight house that can mean condensation on the windows even while the rest of the house feels dry.
• New stuff. Furniture, carpet, paint, cleaning sprays, air fresheners. They give off chemical vapors, the VOCs you've seen on paint cans, and those build up in a house that isn't trading air with outside.
• Dust. Some of it is from outside, but a lot of it is us. Skin, fibers, lint. The furnace blower stirs it every time it runs.

Newer houses have it worse here, which surprises people. A 1950s house in Grand Rapids leaks air around every window and outlet, and that leakage is unplanned ventilation. A house built in the last fifteen years is much tighter. That's great for the heating bill, but nothing gets out unless something is designed to let it out.

Start With the Filter, Because It's Cheap

The furnace filter is the only air cleaner most houses have, and in winter it's working more hours than any other time of year. If it's a one-inch fiberglass filter you can see daylight through, it's there to protect the blower motor. It isn't doing much for you.

Step up to a pleated MERV 8 to 11 and change it on time. In a winter house with pets, that might be every month instead of every three. Pull it, hold it up to a light, and if you can't see through it, it's done. The longer explanation of how high to go, and why MERV 13 in a one-inch slot can choke an older furnace, is in our MERV vs. HEPA breakdown.

One more cheap move: set the fan to run more. On AUTO the blower only runs while the furnace is heating, so on a mild day the air barely moves through the filter. Plenty of thermostats have a circulate setting that runs the fan a set number of minutes per hour. More time through the filter means cleaner air, though it does add some electricity, so try it and see if you notice a difference.

Air Purifiers, Honestly

This is where people spend money they didn't need to.

Portable purifiers. A true HEPA unit, sized for the room, works. It cleans the air in that room. Put it in the bedroom of the person with allergies, run it while they sleep, and they'll likely notice. What it won't do is help the rest of the house, bring in fresh air, or touch gases and humidity. Look for a real HEPA label, not "HEPA-type" or "HEPA-style," and check the room size on the box against your actual room.

Whole-home purifiers. These install in the ductwork at the furnace, and they treat every bit of air the blower moves. A thick media cabinet with a four-inch or five-inch filter is the workhorse here: it catches far finer particles than a one-inch filter without strangling the airflow, and you change it once or twice a year instead of monthly. There are also electronic and UV add-ons that have a place in certain houses. We install whole-home air purification when it fits the problem. It doesn't fit every house.

Ozone machines. Skip them. Anything that cleans by putting ozone into the room is putting a lung irritant into the room. Some of them call it "activated oxygen" or "pure air" or something friendlier. Read the fine print.

One thing the box won't tell you: every purifier, portable or whole-home, cleans the air you've already got. None of them bring in new air. If the house smells stale, feels close, and the windows sweat, a purifier is the wrong tool.

The Fresh Air Problem

A tight house needs a planned way to swap stale inside air for fresh outside air. Opening a window in January works for about ten minutes and costs you heat. The better answer for a lot of homes is a heat recovery ventilator or an energy recovery ventilator, an HRV or ERV.

Both do the same basic job. They pull stale air out, bring the same amount of fresh air in, and run the two streams past each other through a core so the outgoing warm air pre-warms the incoming cold air. You get fresh air without dumping all your heat outside. An ERV also moves some moisture across, which can help keep a Michigan house from getting bone dry in February.

A newer house in Kentwood last winter is a good example. The owner was sure the furnace was making the house stuffy. The furnace was fine. The house was just sealed so tight that nothing got out, and the upstairs windows were running with condensation every morning. What it needed was ventilation, a planned way for stale air to get out, and once it had that the condensation cleared up too.

Not every house needs an HRV or ERV. Older drafty homes usually get plenty of air on their own. If yours is newer, or you've had windows, insulation, and air sealing done, it's worth asking about. An indoor air quality visit is how we'd figure out which kind of house you have.

Dry Air, Gases, and Radon

Winter air in West Michigan is dry, and dry indoor air brings its own complaints: static shocks, cracked skin, scratchy throats, nosebleeds, gaps in the hardwood. That one gets its own article, why your house is so dry in winter, so I'll just say that a whole-home humidifier and the stuffiness problem above can work against each other if nobody's paying attention. Too much humidity in a tight house means wet windows and mold. The goal is the middle, roughly 30 to 40 percent when it's cold out, lower when it's very cold.

Two gases deserve a mention because you can't see or smell them.

Carbon monoxide. The furnace, water heater, gas range, and an attached garage are all possible sources. Every house with gas appliances needs working CO alarms on each level and near the bedrooms. If one goes off, everyone goes outside and you call 911 from there. The full rundown is in our post on carbon monoxide and your furnace.

Radon. It's a natural radioactive gas that seeps up from the soil into basements, and parts of Kent and Ottawa County are known for it. Winter is a good time to test because the house is shut tight. A short-term test kit from the hardware store is cheap and takes a few days. If it comes back high, call a radon mitigation contractor. That's a different trade from ours, and they do good work. The important part is knowing your number.

What I'd Do, in Order

If your winter air bugs you and you're not sure where to start, this is the order I'd go in, cheapest first:

1. Put in a pleated MERV 8 to 11 filter and change it monthly through the heating season.
2. Run the bath fans and range hood every time, and let them run a while after.
3. Test for radon, and check that the CO alarms are working.
4. Watch the windows and a cheap humidity gauge for a couple of weeks. Wet windows and high readings point toward ventilation. Shocks and dry noses point toward a humidifier.
5. If someone in the house has asthma or bad allergies, add a HEPA portable in their bedroom.
6. If those steps don't get you there, talk to us about whole-home filtration or an HRV or ERV.

Plenty of people stop at step two and they're happy. That's fine with me.