Question on vent to outdoors in new house

[aj3]

We had a new house built (in Minnesota) this year, which has a HRV for outside air exchange. Also installed, right next to the HRV is a duct which vents to the outside and then leads down to the basement floor, end in a U shape and simply ends there - so it is effectively an open duct to the outside.
I now notice that a very cold flow of air is coming in through this duct, effectively negating all the insulation and the purpose of the HRV. Can anyone tell me why this is installed, and whether it is OK to close it up (at least for the winter).

Thanks

[majakdragon]

I have never seen this type of vent but I would call the builder to see what it's purpose is. Should be on the prints. Good luck.

[danski0224]

Sounds like you are describing a combustion air intake. This is code in my area if the furnace and/or water heater do not take their combustion air from outdoors.

The correct (and expensive) way to do this is with a motorized opposed blade damper set up to interlock with the furnace. Then the duct is open only when the appliance is on. This approach is common in commercial applications, such as boiler rooms. A continuously open hole to the outside is a bad thing.

Another way to do it is to set the intake duct into a box (or another pipe) a couple of inches bigger in diameter, and about 36" high. Extend the duct from outside to within 2" of the bottom of the other pipe. When combustion air is needed, natural draw will pull it through the larger duct, yet all but the strongest drafts will be stopped. A manual damper in the ducting can help fine tune this, without blocking off the duct.

Many folks plug the duct with insulation after getting occupancy, but if it is installed right, a combustion air intake is a good thing.

The intake allows the appliances to "burn" air from outdoors, instead of air (that you have paid to heat) from indoors. As the indoor air is used and sent up the chimmney, more air must come from somewhere (nature abhors a vacuum). If you do not have a combustion air intake, then that air will infiltrate through gaps in the building envelope (around windows and exterior outlets), commonly known as drafts.

The same thing happens with a fireplace. Start a fire and open the furthest window, you will feel a draft. All that air you paid to heat is going up the chimmney.

If a home is sealed tight, and there are a couple of water heaters, large furnaces and/or boilers, oxygen depletion is a possibility if exterior doors are not opened frequently enough. An ERV helps to prevent this.

[Ed Imeduc]

Id call and check with code there where you are. I know they have come out with some wingding's. We only need make up air if the unit is in a small room alone. What do you have for heat the new gas furnace at 90%????They are direct vent and have their own outdoor air. You dont need any more air for them

ED ;)

[racer766]

Sounds like you are describing a combustion air intake. This is code in my area if the furnace and/or water heater do not take their combustion air from outdoors.

The correct (and expensive) way to do this is with a motorized opposed blade damper set up to interlock with the furnace. Then the duct is open only when the appliance is on. This approach is common in commercial applications, such as boiler rooms. A continuously open hole to the outside is a bad thing.

Another way to do it is to set the intake duct into a box (or another pipe) a couple of inches bigger in diameter, and about 36" high. Extend the duct from outside to within 2" of the bottom of the other pipe. When combustion air is needed, natural draw will pull it through the larger duct, yet all but the strongest drafts will be stopped. A manual damper in the ducting can help fine tune this, without blocking off the duct.

I've been fighting the direct vent/combustion air game for a week now.

New direct-vent Ruud furnace, old flue water heater, tight house. Two qualified sources and two here tell me to do this (big holes into the space with the water heaterfrom the outside...).

Can I use concrete form (laminated paper tube) for the big pipe?

[Jay11J]

Can I use concrete form (laminated paper tube) for the big pipe?

Yes, I've seen people use cardboard box for it.