Is my furnace air return efficient?

May 22, 2011 11:36 AM

In the name of frugality, is this air return on my furnace efficient, or should I cut out the wood and replace with something allowing more air flow? ~650 sq. ft. 2 floor apartment (built ca. 1920s).

It's heating up in Texas and I'm wondering if the makeshift vent for my furnace/ac air return is allowing enough air flow. With regard to furnace size, the label on the side says:

Heater Amps
208/240V
1PH
60HZ

I have no idea what this means. Here's what it looks like, holes about 1 inch dia.

posted by lowdirt to home & garden (5 answers total)

This doesn't quite make sense to me.

I would expect that the cold air return vent duct would be pulling air from some common area of the house...away from the room where the furnace is and there should be a metal duct from the furnace to that grate. In winter, the furnace also needs an air supply for combustion and I'd expect that the holes in the door are for that). I would cut a big square hole that could be covered by the sort of painted metal louvered vent you can buy at most building supply places.
posted by bonobothegreat at 11:52 AM on May 22, 2011

If that is indeed an air return, you can check to see if it needs to do a better job.

Turn on your heater or air conditioner, and station yourself at a floor register (or wherever
the hot/cold air comes out). Position a helper at the door. Check the flow of air coming
out of the vent, and then tell your helper to open the door with the vent in it.

If the airflow increases out of the vent when the door is open, then the vent should be
improved (more holes, or by replacing it with an attractive grill made just for that purpose).
If you don't notice any difference, check the other vents, too.

Take a picture of the plate on the heater and post it. What we really need to know is the
electrical rating of the blower motor, and maybe a BTU rating on your heating and cooling
system.

What you've written means
"single phase, 60 cycle current, at 208 or 240 volts", but you haven't transmitted the
amperage, so we really don't know much about the heating or cooling or blowing rates
of your system.
posted by the Real Dan at 11:54 AM on May 22, 2011

31-1" holes is 122 square inches. Your filter area is probably somewhere between 320 square inches (16x20) and 625 square inches (25x25). I always like to see make up air vents sized to the same area as the filter, especially in the case of holes which present a much greater resistance to flow than a square opening the same size.

So either drill at least twice as many holes or cut a big hole and install some kind of louvred cover.
posted by Mitheral at 12:21 PM on May 22, 2011 [1 favorite]

Thanks everybody.

A note on placement: it's in a short central hallway, with a small bathroom and medium size kitchen on one end and a single large open living/office area with bed (an efficiency).

Here's a photo of the label on the side.
posted by lowdirt at 12:33 PM on May 22, 2011

It should be noted that the lion's share of the electricity an air conditioner uses goes to making the coil cold. Mitheral's advice seems pretty solid to me, but right now you've probably not any worse off than the legion of people out there who change their air filter once a year or so. (That being said, Gah!)

You're not suddenly going to cut your electric bill in half, but it will be a little less stain on your motor and a bit more air movement.

(If it were my door I'd look into doing something like this. If you're only renting, that would be harder to justify.
posted by Kid Charlemagne at 1:02 PM on May 22, 2011