Cleaner Indoor Air on a Budget: Filters, Ventilation and Gas Stoves

The EPA says Americans spend about 90 percent of their time indoors, and that indoor levels of some pollutants are often two to five times higher than outdoors. The usual sources are ordinary: cooking, especially on gas, dust, wildfire smoke drifting in, damp basements, and radon seeping up from the soil.

None of the fixes below are expensive. They do cost a little to run, so this is one of the few GreenLife guides where the yearly figure goes up, not down. If you or anyone at home has breathing symptoms, see a doctor; better air helps, but it is not a treatment.

Start with the furnace filter

If you have forced-air heating or central AC, the cheapest air cleaner in the house is the filter slot. The EPA recommends MERV 13 or the highest rating your system can accommodate. MERV 13 catches a large share of fine particles, including smoke; the cheap fiberglass filters many homes use are rated MERV 1 to 4 and mostly protect the blower from lint.

A 1-inch MERV 13 filter costs $15 to $30 and lasts about three months. Denser filters restrict airflow, so check your furnace manual or ask your HVAC technician before you switch, especially on older systems. A 4-inch media filter cabinet, if your system has room, gives better filtration with less resistance and lasts six to twelve months. Set the thermostat fan to run more often on smoky days; the filter only works while air moves through it.

A portable cleaner for the bedroom

If you have no central system, or want extra filtering where you sleep, a portable HEPA air cleaner does the job. Look for the Clean Air Delivery Rate (CADR) on the box: a rough rule is a smoke CADR of at least two-thirds of the room’s square footage, so 100 or more for a 150 sq ft bedroom. ENERGY STAR certifies air cleaners, and certified models use noticeably less power.

The budget version is a box fan with filters taped to it. Four 20×20 MERV 13 filters taped into a cube with a box fan on top, often called a Corsi-Rosenthal box, cleans a room about as well as a mid-range purifier. It costs $80 to $130 to build and is louder. The EPA includes DIY fan filters in its wildfire smoke guidance. Use a newer fan (2012 or later) and don’t leave it running unattended for long periods.

Cooking fumes and gas stoves

Gas burners release nitrogen dioxide and carbon monoxide along with heat. Research has linked gas stove use to higher indoor nitrogen dioxide, which can irritate airways, particularly in people with asthma. Frying and searing on any stove also release fine particles.

• Use the hood every time, on the back burners, and leave it on for 10 to 15 minutes after cooking.
• Check that it vents outdoors. Many hoods over the range only recirculate through a grease screen, which does nothing for cooking gases. Adding a ducted hood costs $400 to $2,000 installed, depending on the duct run.
• If there’s no hood, open a window and run a bathroom or window fan.
• A portable induction burner costs $60 to $150 and plugs into a regular outlet. Doing most everyday cooking on it means the gas burners rarely come on.

Humidity, carbon monoxide and radon

The EPA recommends keeping indoor humidity between 30 and 50 percent. Above 60 percent, mold and dust mites thrive; very dry air irritates noses and throats. A $10 to $15 hygrometer tells you where you stand. A dehumidifier in a damp basement often does more for air quality than any purifier.

Radon is the one you cannot see, smell or guess. The EPA estimates about 1 in 15 US homes has radon above its action level of 4 picocuries per liter, and calls radon the leading cause of lung cancer among people who have never smoked. A short-term test kit costs $15 to $30, including lab analysis. If the result is 4 or higher, retest, then get a quote for mitigation, which usually costs $800 to $2,500. Some states offer free or discounted test kits; check your state radon program on epa.gov/radon.

1. 1

   Check your furnace manual 10 min · free

   Find the filter size and the highest MERV rating the system allows.

2. 2

   Buy filters and a hygrometer $40–$70

   Order a year’s supply of filters so you change them on schedule.

3. 3

   Test for radon $15–$30

   Place the kit in the lowest lived-in room for 2–4 days and mail it to the lab.

4. 4

   Install CO alarms $20–$50 each

   One per level and one outside each sleeping area.

5. 5

   Add a bedroom cleaner $80–$300

   Build a box-fan filter or buy a HEPA unit sized for the room.