Wouldn't the furnace need to run to push air past the filter? I feel like not many people are running their furnace in the summer.
this post was submitted on 23 Jul 2026
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AC reuses the same fan that goes through the furnace. Even though the furnace is not on the fan still blows air through it. My heat exchanger sits above the filter, which sits above the furnace
It depends. Those systems aren’t always tied together, especially in older homes.
Mine, for example, is old enough that the house is heated with a boiler pushing hot water through pipes in the floor.
Fair, good point
No but I changed the ones on my CRboxes because they're really doing the heavy lifting.
Edit to add link because I had no idea what that was a few months ago either.
I've seen those before and even made one once, didn't know that's what they were called though. Thanks for that
I have no idea why those boxes are credited to those two. These were a thing in the 90s.
Probably only because they brought them more main stream. My brother made something similar prepandemic as well.
Sweet, I didn't know they're name, but I thought of building one from a larger automotive filter that's a cylinder. It's probably not HEPA, but I thought it'd look cool lol
There's some cool ones on reddit r/crboxes made with computer fans
No way can a computer fan push enough air for that application.
One? No. 5? You'd be shocked. Significantly more pull than most stand alone air purifiers.
It's a box filter. For some reason to the design was credited to those two. They used them in the Manhattan project.
ours was changed back in January, we pay a yearly sub to our oil company that locks in our price per gallon for the year and also includes maintenance and parts if something went wrong as a result we don't touch it! I also don't think the smoke is visible or noticeable where I am yet.
HVAC fans do a poor job at filtering. You are better off with room HEPA air filters than straining the furnace AC fan with high MERV filters. Quite the scam claiming they filter out allergens or smoke.
No, but I had to change all the AC filters.
changing mine this weekend. (Checked it a couple times during the ash-pocalypse).
In those conditions I just change it every 2 months. I moved and change it once a year but not really in a fire area anymore
The furnace doesn't run when it's hot, so it'll be fine. (No AC is still common in Canada)
Oh. In US, a lot of central AC units still utilize the central furnace blower fan and air filter to circulate the cooled air.