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Old 09-21-2012, 11:55 AM   #1
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Combustion Air Vent Troubles


Were renting a slab house with a utility / HVAC room off the dining room with a large rectangular combustion air vent in it. The forced air and ac unit as well as the water heater are fairly old, the house was built in the late 80's. The vent is a good distance from the units probably 3 or 4 ft from the heater and 5 or 6 ft from the water heater. I am no expert by any means but I can tell its not the most efficient, unfortunately its what we can afford and in a nice area.
The cold from the vent has been causing some freezing issues with the water pipes in the utility room for the washer and the feed to the house. It gets very cold in the utility room with New England winters. I have sealed the forced hot air vent for the utility room in the ceiling because it seemed like a complete waste of money.
My question really is do any of you know of a way to seal off the side of the utility room with the hvac and water heater without major damage to the house? I am not trying to seal off the vent, I would rather pay extra to heat and keep my family safe. I hung a tarp up last winter but it didnt really do much other than make me imagine it was warmer and make my wife complain about it.
Any ideas on this one is greatly appreciated thanks in advance.

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Old 09-21-2012, 01:47 PM   #2
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Combustion Air Vent Troubles


Is the outdoor air supply powered and interlocked with the combustion equipment?

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Old 09-21-2012, 05:55 PM   #3
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Combustion Air Vent Troubles


So I take it that the combustion air vent is from outside...how big is it? has there been a calculation to determine if it is over sized..you may be able to downsize..also, if you have an interior door to the HVAC room you may be able to leave it open and close off the outside air vent..OR just provide a grill in the interior door to provide combustion air from the house..check with local gas codes..I presume the furnace IS gas fired...it is not unusual to provide inside air to the mechanical room for combustion...this may be all you have to do..it's worth getting your fuel supplier rep or a local tech to advise you on this
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Old 09-21-2012, 06:56 PM   #4
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Combustion Air Vent Troubles


When you say vent...is it just a hole in the wall or is there ductwork? What is commonly done is install a duct with a couple of elbows at the bottom. What this does is traps the air until the furnace or water heater requires it, then it siphon's it out "as needed". This may help your cold room situation. I'm sure there are other ways to handle this but that way does work.
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Old 09-21-2012, 10:27 PM   #5
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Combustion Air Vent Troubles


Thanks for the replies!
To answer some more questions:
The vent is not connected to the natural gas furnace or water heater. It's a rectangle roughly 10x12 in with small slats and a screen fairly low to the ground. There's no ducting at all on it just the vent into the room.
There are 2 doors one to the garage and one to the dining room, the utility room is open and shared with the laundry.

I am not positive what powered and interlocked means but I'll start googling it after.
I will give my utility company a call and see if there's a tech for some advise.
The duct with elbows sounds like a good idea as well, that's another thing to look into.
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Old 09-21-2012, 10:48 PM   #6
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Combustion Air Vent Troubles


Not sure how a utility company would have anything to do with it.
Look around on the unit and see if there's a sticker on it from a company that's serviced it before.
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Old 09-22-2012, 07:20 AM   #7
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Combustion Air Vent Troubles


Posting pics of the set up may help us help you.
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Old 09-22-2012, 09:26 AM   #8
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Combustion Air Vent Troubles


Joe Caption..where I live here in Ontario Canada..the utility/gas supplier is responsible to inspect and enforce the code(s) OR indirectly through any gas techs who service the unit therefore, the local gas supplier should know if the OP can eliminate the outdoor combustion air..Other than sealed combustion type units as long as the furnace door is open to the rest of the house OR has a louvre open to the rest of the house he should be able to close up that outside combustion air opening. As for interlocks ..they are electrical limit switch on damper of out side aire that would allow you to keep the outside air closed until the furnace stat calls for heat then the furnace will not be energized until the louvres open. and activate a switch completing the control circuit to the furnace. This set up also requires a motor to open the louvres etc. In my experience (IME)( did I just start a new acronym for this forum?) this is usually only used in commercial industrial/applications.
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Old 09-22-2012, 08:22 PM   #9
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Combustion Air Vent Troubles


If the vent is used for combustion and ventilation, you could seal the vent to the outside and take the door off the utility room. You could also install two vents on a wall or door to the utility room to provide enough make up air from inside your home. One vent must be 12in from the ceiling and the other 12in from the floor. Vents must be at least 100 sq inches. Louver door will work also.
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Old 09-22-2012, 09:25 PM   #10
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again I think the requirements are being over stated here..Combustion air is required but can be from air withhin the house therefore, you can eliminate/close off the outside combustion air source..."ventilation" air is not required in this domestic application so, you do not require upper opening as described..that is, of course if your codes are similar to here in Ontario which is likely as we are pretty stringent here..

"ventilation air" an opening not less than 10% of the combustion air opening..placed as close to the ceiling on outside wall to allow escape of combustion by products which may escape into the appliance (furnace) space....DEPENDING on rated gas input of furnace/boiler etc. I believe usually only with inputs exceeding 400,000 BTUH so, should not be applicable here. Don't have latest gas code book.

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