Do window AC units pull air from outside?
We don’t usually wonder from where the cold air comes from. However, when you see wildfires burning, and the sky being orange from all the smoke, you don’t really want all that dangerous smoke in your home.
Window AC filters (usually MERV 14 rated filters) are certainly not adequate to stop the wildfire smoke if your unit pulls the air from outside.
If you read some articles about ‘does window air conditioner pull air from outside’, you might get a partially wrong idea. That idea is that ‘No, window AC units definitely don’t pull air from outside, they just recirculate the indoor air’. That, however, is not entirely true.
Certainly, most window air conditioners don’t pull air from outside. But not all.
In this EPA’s recommendation, you might find a clue why that answer is partly wrong:
“If your HVAC system or window air conditioner has a fresh air option (meaning it pulls in air from the outside), turn it off, close the intake, or set the system to recirculate mode.” (EPA recommendation for indoor air quality during wildfire)
Now, let’s get the record straight:
Some window AC units don’t pull air from outside. Some window AC units do pull air from outside.
Luckily, there are not many window AC units that pull air from outside. But you don’t want to be that guy who thinks he or she has a standard no-air from the outside window AC only to be proven wrong when window AC starts pulling in wildfire smoke.
In most cases, window AC units that pull air from outside are better (higher energy efficiency, no negative pressure problem, no stale air). However, in limited cases, having a window-mounted air conditioner is not ideal. Some of these cases include:
- Wildfire season.
- Living in an area with low outdoor air index quality.
- Window is above a busy street.
The key question is not if window air conditioners pull air from outside. It’s this one:
Does My Window Air Conditioner Pull Air From Outside?
If it doesn’t, you’re all good running it even during wildfire season. If it does, however, you want to shut it off completely or just shut off the fresh air option.
Here’s how to tell if you have a window air conditioner that pulls air from outside the house:
- Every fresh air window air conditioner will have a ‘Fresh Air Mode’ mode.
- If it has one, you will find it on your AC dashboard, remote control, or in the Wi-Fi connected app that sets the window AC settings.
If turned ‘On’, the fresh air vent located on the outer part of the unit (the part that sticks outside) will be open. When the fresh air option is turned ‘On’, this vent will draw in outdoor air.
This will reduce the negative pressure window AC units can cause (because they are only expelling air and thereby reduce the total air quantity inside) but it will pull the smoke-filled air in.
Do you need to shut down a window air conditioner during a wildfire if you find this option?
Not at all. If you do find this option and there is wildfire smoke outdoors, you know what to do:
Just turn it ‘Off’.
This will immediately close the fresh air vent, and you won’t be pumping smoke-filled air indoors.
Note: Central air conditioner can have the same ‘Fresh Air Mode’. Be sure to turn it ‘Off’ during the wildfires season.
What To Do If The Smoke Is Already Indoors?
Usually, when we have smoky air indoors, we just open the windows. In this case – when outdoor air is contaminated by wildfire smoke – you can’t really do that.
How to get rid of indoor smoke during wildfire season?
Recently, we have published an article about how to smoke indoors without it smelling. Under #5 tip you will find a solution that works well for wildfire season.
To get rid of the smoke and improve indoor air quality, just get an air purifier. Air purifiers have two filters that deal with any smoke, even wildfire smoke, very well. These are:
- HEPA filter. This fine filter captures smoke particles.
- Activated carbon filters. This filter adsorbs gaseous smoke odor.
Pretty much any air purifier with these filters will work. The ones that work the best are air purifiers with high smoke CADR rating (a metric that tells you how efficiently air purifier reduces the concentration of 0.9 and 1.0 μm sized smoke particles).
If you need some help with picking an effective air purifier, you might find our article about the best air purifiers for wildfires here helpful.
Summary: Most Window AC Units Don’t Pull Air From Outside (But Some Do)
Here’s the bottom line:
Most window AC units don’t have fresh air vents that would suck in air from outside.
The key is to check if your unit has one. You can do that by checking if it has ‘Fresh Air Mode’ on the units’ dashboard, remote control, or the controller smartphone app.
Even in that case, you can just turn it ‘Off’ and avoid the wildfire smoke being pulled into your home.