If portable air conditioners bring in outside air is primarily a wildfire issue. Namely, when the sky is almost orange from wildfire smoke (forests in Canada or California burning), you don’t want a portable AC unit to pull air from outside. Let’s answer this in ‘Yes and No’ style, and explain if and why portable AC units bring air from outside.
Here’s the deal:
Some portable air conditioners don’t pull the air from outside. Others do.
Note: There is a way to use every portable AC unit during wildfires, even if it pulls air from outdoors; we’ll explain why (using indoor-indoor airflow).
Specifically, we have these 2 types of portable air conditioners:
- Single-hose portable AC units. These have only 1 exhaust hose. This hose pulls hot air from indoors to outdoors only. That means that one-hose portable air conditioners don’t pull air from outside.
- Dual-hose portable AC units. These have 2 hoses; 1 exhaust hose and 1 air intake hose. The exhaust hose works the same as in the case of single-hose AC units. However, the air intake hose does suck outdoor air indoors. That means that dual-hose portable air conditioners do pull air from inside.
Now, a portable AC unit pulling in air from outside is usually a very good thing (no negative pressure, higher efficiency). However, in the case of wildfire smoke, it is an awfully bad thing.
That means that:
- You can run a single-hose portable AC unit even during wildfires. It will not suck in the smoke.
- You should shut off a dual-hose portable AC unit during a wildfire. It will bring the air (along with the smoke) inside. Check below to see how you can still use a dual-hose portable AC unit during a wildfire (there is a trick).
One of the most commonly asked questions here is this: Do portable AC unit filters stop wildfire smoke?
In general, the correct answer is ‘No’. Portable AC units use MERV 8, MERV 11, MERV 13, or even MERV 14 filters. These are not fine enough to stop wildfire smoke from entering your house (in the case of a 2-hose portable AC unit). HEPA filters could stop all that smoke but you cannot use a HEPA filter in a portable AC unit (it would restrict airflow way too much, leading to unit failure very quickly).
Let’s quickly look at why single-hose portable AC units are better than dual-hose portable AC units during a wildfire:
Where Does A Portable Air Conditioner Pull Air From?
Here we should be looking at this article about how portable air conditioners work.
Both single-hose and dual-hose portable AC units pull the warm indoor air via the front. Both also expel cooled air indoors and expel the hot air outdoors with the exhaust hose.
Only expelling air outdoors will create a lower indoor pressure. That is a problem; low indoor air pressure means the fan must work against pressure to expel air outdoors. The fan will have to work extra hard, use more electricity, and will thus be less energy efficient. To solve this issue, dual-hose portable air conditioners were created.
Here is the key single vs dual-hose portable AC difference that is very relevant during wildfires:
The dual-hose AC units have a 2nd hose that brings air from outdoors inside.
In such a way, the negative indoor air pressure is normalized again. However, as we now know, it does come at a cost:
Bringing outdoor air indoors via the 2nd hose is all good and well (when the air is clean) unless there is a cloud of smoke from the wildfires in the outdoor air.
The dual-hose portable AC unit presumption is that the outdoor air will always be cleaner than indoor air. However, due to frequent wildfires in 2021, 2022, and 2023, the outdoor air is not always cleaner. In fact, it can be filled with wildfire smoke that we don’t want in our homes.
Here Is How To Use Dual-Hose Portable AC Unit During Wildfires
A little-known trick with dual-hose portable AC units is that you can use it during wildfires, despite that 2nd hose pulling air from outside.
Namely, the 2nd hose just transports air. That’s it.
If you pull the 2nd hose inside the room, it will only pull air from inside the room. You will still have airflow through 2nd hose, but it will be indoor-indoor airflow, not outdoor-indoor airflow.
All in all, dual-hose portable AC units are better than single-hose unit. However, due to these frequent wildfires, choosing this “better” dual-hose portable AC unit can backfire because this type of portable air conditioner pulls smoke-filled air from outdoors.
If you have a window AC unit, you should also check this explanation on window AC units pulling air from outside.