Before you buy anything, try one free change for a night: leave the bedroom door open a few inches, run the ventilation you already have, or crack a window. If one of them brings your bedroom down to the goal, 800 ppm or less on average while you sleep, and you can keep doing it, you may not need anything else.
Start from your baseline
A free fix only means something when you can compare it with something. That's your typical night from a fair check of a few ordinary nights. Every experiment below is measured against that number.
Change one thing per night
If you open the door and the window on the same night, you won't know which one helped. Change one thing and keep everything else the same as your baseline nights: the same people, the same monitor spot, the same heating or cooling settings.
One night is a clue. Two nights that agree are a result. If a change looks promising, repeat it once before you decide.
Experiment 1: Leave the door open a few inches
An open door connects the bedroom to the bigger volume of air in the rest of the house. In a study of new homes in Scotland, bedrooms with closed windows averaged about 2,000 ppm overnight when the door and small window-frame vents were shut, and about 1,550 ppm when only the door was open. Bedrooms with both the door and vents open averaged about 1,000 ppm. Those were different bedrooms rather than one room tested both ways, but the pattern is clear enough to be worth testing in yours. Notice, too, that even the best of them sat around 1,000, above the 800 goal: an open door helps most when the rest of the house is well ventilated.
There's a real trade-off. Fire-safety researchers at UL's Fire Safety Research Institute recommend sleeping with the bedroom door closed. They say a closed door can mean the difference between about 1,000°F and 100°F in a fire, and can hold carbon monoxide to a fraction of the level in an open-door room. A door left open a few inches gives up some of that protection.
So treat this one as a measurement first. If it works, talk with your household about whether a permanent open door is a trade you want to make.
Experiment 2: Run the ventilation you already have
If your home has a ventilation system, such as a heat or energy recovery ventilator or a continuously running exhaust fan, check whether it has a boost or higher setting and try that for a night.
If you don't have one, you can set your thermostat's fan from Auto to On so the furnace fan runs all night. The EPA suggests running HVAC fans on the On setting so air passes through the filter continuously. Be clear about what this does, though. The EPA also notes that most home heating and cooling systems, including forced-air systems, "do not mechanically bring fresh air into the house." The fan mostly mixes the bedroom's air with the rest of the house. That can still help a closed bedroom, but it adds outside air only if your system has an outdoor-air intake.
A few cautions:
- Don't switch off, turn down or block any ventilation that is meant to run all the time. Boost is fine if your system offers it.
- Running a fan all night uses electricity and makes some noise. Check that both are things you could live with long term.
Experiment 3: Crack a window
The EPA notes that opening windows when the weather permits increases how much outdoor air comes in. It's the most direct route for outside air, and also the experiment with the most conditions attached.
Only try it when:
- Outdoor air is clean. The EPA advises against ventilating with outdoor air when outdoor pollution or humidity is high, and suggests checking AirNow.gov. During wildfire smoke, it advises keeping windows and doors closed.
- The weather allows. Very cold, hot or humid nights can make an open window uncomfortable or impractical.
- The window can be secured. Use a lock or stop that limits how far it opens, especially on the ground floor or in a child's room.
Reading the result
The next morning, compare the night with your typical night, and with 800.
- It reached 800 or less, and you can keep doing it. Repeat it once to confirm. You may not need to buy anything.
- It helped, but not down to 800. Try a second night, or try a different single change on another night. Getting a bedroom to 800 shows how much fresh air the room needs.
- Little or no change. That's useful too. It suggests the room needs a different way to get outside air.
When a free fix works but doesn't fit your life
Sometimes a change works but can't happen every night. Windows may need to stay shut through winter or wildfire season, and some households will choose to keep the bedroom door closed for fire safety.
In that case, a balanced ventilation system can do a similar job in the background with the door and window shut. The EPA describes energy-efficient heat recovery ventilators as one kind of mechanical system that brings outdoor air into the home. If you reach that point, the app can help you collect installer quotes and then recheck the room afterward.
Tonight: Try one free change
- Pick one change: the bedroom door open a few inches, your ventilation on boost or the furnace fan set to On, or a window cracked if weather, outdoor air and security allow.
- Keep everything else the same as your baseline nights: the same people, the same monitor spot, the same heating or cooling settings.
- Write down the change and when you made it, then sleep as usual.
- In the morning, compare the night with your typical night and with the 800 ppm goal. If it helped, repeat the same change one more night to confirm it.
Sources
- US EPA: Ventilation and respiratory viruses
- US EPA: Improving indoor air quality
- US EPA: Wildfire smoke, strategies to reduce exposure indoors
- UL Fire Safety Research Institute: Close before you doze
- International Journal of Environmental Research and Public Health: Occupant interactions and effectiveness of natural ventilation strategies in contemporary new housing in Scotland, UK (Sharpe et al., 2015)