Furnace ventilation freezing me out
yokel
| Posted in Energy, Heating & Insulation on
Im wondering about the duct that supplies fresh air to my furnace. I’ve got a 6″ piece of duct that comes into the furnace closet and bends downward toward the base of the furnace and stops about a foot off the floor. I can feel cold air just flowing into the house…I know a furnace needs ventilation but this is rediculous…Anyone know a better way? Maybe a vent with a flap that opens when the heater comes on? Could it be a smaller pipe? Any ideas would be greatly appreciated!
Replies
If you have the install manual it usually list the size of the supply vent needed for combustion air. A big, honking furnace may actually need a 6-inch duct to keep it happy.
Bringing cold, outside air into a living space is kind of crazy when you think about it, and that's why direct vent appliances make more sense in cold climates.
We're finishing our basement now and closing off the utility room, however, it's still 'open' air-wise (ceiling joists will remain exposed as will access to the larger laundry area via the space underneath the stair, which, too, will have open ceiling joists to the finished space.)I've always read that we should have these 'cold air pipes', but at the same time, we've never had any CO issues (2 CO detectors in the basement). Granted, this house was built in 1927, so I wouldn't call it air-tight either.Am I 'living dangerously' with this set up or should we have the ducts coming in? It just feels very wrong having a 6" hole in your wall in MN in January to help 'heat' the house. Is the bucket method a sufficient enough air trap? Being that this is the basement, several inches of frigid air at the floor line isn't going to be comfortable.Our heating guy is coming out next monday so will see what he suggests as well.I agree that direct-vent is the way to go and it's rather odd that there aren't already more of these out there.Are there such things as 'direct vent converter kits' to convert existing systems to a more direct-vent system?Given that our HW heater and Furnace are on a raised 4" slab, I thought one option would be to wrap the slab in a 12" sheet metal lip and dump the vent into that...creating a 'bucket' just for these appliances.The catch is that even then it's still 6' below ground level so I imagine cold air would still 'overflow' this and spill out into the rest of the finished basement.
You might ask about a heat recovery ventilator. The HRV will temper the incoming air so it's not as cold, but they cost $500 to $2K plus installation, so it might not make economic sense for just one room.
I'm an electrical guy so I'm not an expert on HVAC stuff, but I see the stick-the-vent-in-a-bucket arrangement all the time on commercial and municipal construction projects here in Minnesota and it seems to work okay. They actually use a box formed from sheet metal, but a bucket would accomplish the same thing.
Are you referring to Make Up Air to combat negative pressure in your house or a vent for combustion air?
If you're talking about MUAU that should have a damper on it. If you're talking about combustion air, where is your furnace (in a closet, etc)?
I think a furnace would have to be in a pretty "tight" room to require a vent for combustion.
I think I could use a little more info.
Thanks for the info. It's in a closet sized room, but I presumed it was for combustion. The house isn't super air tight, but I'm working on it. When i put my hand under the duct I can feel cold rushing in, and I'm in the rockies...
Yes, the purpose of the duct is to bring in combustion air, in order to prevent "starving" the burner (which can lead to CO problems), and so that the furnace doesn't draw combustion air from the rest of the house.Keep in mind that air will only come in through that duct if it's going out somewhere else. Ideally the only place it's going out is the flue, and the air is only coming in to any degree when the furnace burner is lit. Having the duct actually saves heat because you don't create a vacuum in the house and draw in cold air elsewhere.Try this: Check the airflow from the duct with the furnace fan running (but no burner) and with it not running. If there's a substantial difference between the two then it means that there's probably ductwork in the attic or crawlspace or wherever that's leaking air to the outside. Fixing that should be your first priority.
If your view never changes you're following the wrong leader
I just had a tankless h20 heater installed here south of Denver.
The BI that came by to inspect marveled at the installation, space saved and while looking at the flues, mentioned, "you don't need this outside air inlet anymore with these sized flues. Cap this high one and slip an empty 5 gallon bucket under the low one so it acts like a trap. It'll hold the cold air inside the bucket and keep the drafts down."
Cheep fix.
Edited 11/27/2007 8:43 am ET by peteshlagor
Great idea- thanks...
If the closet sized room has a louvered door, you may not need an outdoor air source. The important thing is to not starve the combustion.
But it should be noted somewhere here that the air duct is probably required by code, at least the code that was current at the time the house was built.
If your view never changes you're following the wrong leader
If there's that much air coming in through that duct it's because air is escaping from the house elsewhere. You need to find and fix the air leaks.
"If there's that much air coming in through that duct it's because air is escaping from the house elsewhere. You need to find and fix the air leaks."Yes, it is called the vent.I have the same "problem". 2 gas FWHA furances and a WH in a closet.You need to have Free Communications with the larger part of the house to not have to have bring in outside combustion air.When I replace the furnaces I am going to try to do with a direct vent furnace and WH..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
My HVAC contractor installed a motorized damper in mine at least 15 years ago. When the furnace calls for heat it opens and then closes when heating cycle is done. Has worked great with no issues since installed. That way cold make up air is not coming in when the furnace is not needing it.
Jay
Simplest fix is to add a barometric damper. Pick one up at a HVAC supply house, or have your HVAC contractor install one fo you.
Ajust the spring tension so the damper opens when the furnace or water heater comes on and pulls slight negative pressure on the room. When the appliance shuts off the spring will close the damper.
You do have to be carefull with these though. If your combustion air pipe is in an area subject to moderately high winds they won't open because wind crossing the pipe creates a venture affect, making the inside of the pipe have a negative pressure in relation to the mechanical room. It doesn't sound like you would have this problem though, because your open pipe is constntly dumping cold air into the room.
Dave
Dave
Dave