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Old 02-28-2010, 11:30 AM   #1
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Hidden cold-air return


For a while, I've noticed that when the furnace comes on, it comes on with a loud bang. I had it professionally cleaned & inspected in Dec 09, and asked about the loud noise (loud enough to wake me out of a dead sleep). They furnace guy said it's due to the large amount of air it has to draw in when it gets started. In my bungalow, there is a cold-air intake on the main floor, but not one in the basement. A couple of years ago, we had a flood in the basement (washer malfunctioned), & I could swear there was a cold-air intake in the basement low on an interior wall. The guys who fixed the basement after the flood had to take drywall down & put new stuff up, exactly where I remember the intake. I'm wondering if they covered the intake over with drywall. If so, how do I go about finding it and correcting the problem? Will my furnace be any quieter with another intake? Any and all input appreciated!

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Old 02-28-2010, 11:37 AM   #2
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Hidden cold-air return


It will be quieter with another intake and make life easier for the furnace and extend its life. Only way to know is to do some exploratory surgery (open the wall or poke small holes with a nail) where you think it was. You may be able to follow the duct from the furnace to that area thru the ceiling joists to narrow it down.

Good luck and enjoy the snow.

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Old 03-01-2010, 07:28 AM   #3
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Hidden cold-air return


Thanks for your reply. In the meantime, I found an old photograph taken in that room which shows a cold air return on the wall near the floor so now I have half a clue where to start. Another question: There's a metal box (for lack of a better description) on the ceiling in the basement leading to the furnace. It's location corresponds to the cold air intake on the floor above. Right under the box in the basement, the wall juts out a couple of inches by about 6" wide, going all the way to the floor. What's the likelyhood that the duct work is in there? Also, if I tap on the wall and there's ductwork behind it, will it made a noticeably different sound than if it were hollow? Thanks again!
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Old 03-01-2010, 05:46 PM   #4
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Hidden cold-air return


Take some pics of it, so we can see. It should have a hollow sound IF the rest of the wall is insulated with fibreglass pink which would deaden any sound. Try banging on the wall with a rubber hammer to see if the sound changes.
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Old 03-02-2010, 04:23 AM   #5
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Hidden cold-air return


let's just hope the drywall guy didn't get mad at his helper . You might find a surprise in the wall
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Old 03-02-2010, 06:29 AM   #6
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Take some pics of it, so we can see. It should have a hollow sound IF the rest of the wall is insulated with fibreglass pink which would deaden any sound. Try banging on the wall with a rubber hammer to see if the sound changes.

Pretty sure there's no pink insulation in there. We took the baseboard off last night & cut some holes near floor-level. When we turned the furnace on, we couldn't feel any air being drawn up thru any of the holes. When we tap on the wall everything except the studs sound hollow but about 6" from the top of the ceiling, it sounds like something is there. Do you HVAC guys have any way of determining where the metal ducts may be? Metal detector, x-ray vision, anything? Cheers!
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Old 03-02-2010, 07:16 PM   #7
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Old 03-02-2010, 08:06 PM   #8
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let's just hope the drywall guy didn't get mad at his helper . You might find a surprise in the wall

Well, that would explain the odd smell...............
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Old 03-02-2010, 08:19 PM   #9
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Crystal Ball
Aahh, I thought as much! I'd like your opinion on this: my hubby spoke to his co-workers and one of them said he thought that if we cut a hole thru the wall the size of a cold air return across from the furnace, that should be enough extra air for the furnace to work better. There's already a doorway from the rec room to the furnace/laundry room but he said that wasn't enough. What are your thoughts? I thought there would have to be a duct to draw air directly into the furnace, but I am certainly no expert! That's why I'm on here...............
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Old 03-02-2010, 08:28 PM   #10
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Hidden cold-air return


I would literally have to be there and see what you have. Not sure how much a WestJet ticket is to TO and the weathers great here. LOL. You can have a return air grill installed in the rec room but it needs to be connected to a return duct which goes back to the furnace. You cannot do that INSIDE the furnace room as it can depressurize the room/suck fumes into the house from the water heater/etc etc and it is illegal.
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Old 03-02-2010, 08:54 PM   #11
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Glad I asked! The water heater is electric, but cutting a hole thru the wall doesn't sound like a good idea anyway
Co-worker should stick to putting cans on a shelf!

Last edited by GirlCanBuild; 03-02-2010 at 09:03 PM.
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Old 03-02-2010, 09:10 PM   #12
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Hidden cold-air return


Kind of sounds like you might be talking about combustion air grills and not return air. Should be 50 cubic feet of free air available for every 1000 BTU.
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Old 03-03-2010, 07:06 AM   #13
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Hidden cold-air return


Combustion air grills? Not sure what that is. If thats the case, would I be able to just make an opening in the wall between the rec room & furnace room, so that the furnace can draw more air? Thanks for the reply

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Old 03-03-2010, 07:15 PM   #14
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Hidden cold-air return


In order to provide the proper amount of oxygen for the fire to burn correctly there needs to be 50 cubic feet of free air space for every 1000 BTU's, that's combustion air. It can be brought into the furnace room from outside or other rooms via holes in the walls covered by grills for looks. Need to look a the furnace BTU,get the tape measure out and get to ciphering.
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Old 03-03-2010, 07:28 PM   #15
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Hidden cold-air return


You need more air returning to the furnace fan thru the return duct and not combustion air (different topic).

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