Do I really need two air filters for my heater?

October 26, 2007 7:56 AM

Do I really need two air filters for my heater?

I rent an apartment with forced air heating. While doing some cleaning I noticed that the intake on the furnace had a lot of dust so I opened the grate and found a two stacked air filters wedged between the grate and where the heater begins behind the wall. The first one was filthy but the second one wasnt looking too bad. I replaced them both by buying new ones at home depot. While trying to find the proper size I read that one of these is "low flow" or something like that which helps with efficiency.

Considering that the current set up is two filters stacked on top of each other, am I hurting efficiency? Can I just leave one filter in there? I'd ask the landlord but his english isn't so good. Thanks.

posted by the ghost of Ken Lay to home & garden (3 comments total)

Depends on the heater, actually. If they're "wedged" in there, they're not the right filters, they should fit in just about perfectly. Don't assume that the filters that are there are the correct filters. If you have any idea what brand the furnace is, and if you can find a model number, you might call a local furnace shop and ask them for the filter number you need.

But you probably don't need two, assuming one fits. I have seen furnaces that use two, though.
posted by TomMelee at 8:08 AM on October 26, 2007

It could be a system that uses a rough filter followed by a fine filter. The idea is that the rough filter will cost less and remove large particles. This filter will be changed at x times the rate of the more expensive, finer filter.
You would find out more by identifying the furnace.
posted by kuujjuarapik at 10:31 AM on October 26, 2007

My guess is the installers set the system up to use 2" filters, which can be hard to get, except through heating supply firms or in bulk orders, and are hard to find in high-efficiency models. The boobs who installed the furnaces in my complex did this -- they probably had an overstock of 2" boxes or filters they unloaded on us.

This sucks if you don't want to have to live by counter service hours, and just want to pick up a new filter at Mega-Lo-Mart on the way home. The kludge suggested by my furnace guy (not the banana who put the system in) was to either use two 1" filters, or a 1" filter and some spacers.

Anyway, this sounds like what you're looking at.
posted by Opposite George at 11:29 PM on October 26, 2007