I live in a typical new subdivision located in Michigan. The house was built about 2 years ago and we just moved in last summer, so this is our first winter (and a pretty cold one right now...)

In the fall I noticed that on the back of the house, there are two 'vents' since my basement is finished, I went into a neighbors basement and found that his was set-up the same. It seems that both of these 'vents' are connected to insulated flex duct. One appears to tie into the cold air return and the other just ends (not capped, just open) in the mechanical room.

I was checking my furnace filter today and put my hand by the flex duct that is open and was quite shocked with the amount of cold (really cold) air coming in.

I suppose the builders thought the house would be so tight that they would need outside fresh air. No heat recovery unit is present.

Should I:

1. Ignore it.
2. Block the vents from the outside.
2. Block the one tied into the cold air return and investigate installing a heat recovery unit.

I'm open o thoughts.

Thanks

Ian.

My house in Minnesota had a similar set-up.

The duct to the mechanical room is code required for make-up air for your (gas) furnace and water heater.  If you do not have gas or oil (i.e., no combustion) it is probably not required.  My utility room was reasonably well sealed and it was not a space conditioning problem for me.

I added an outside air connection to the return air side of furnace to pressurize the house to mitigate smokey air infiltration through the damper on my exterior wall fireplace.  Pressurizing the house helped a bit.  It did not have a noticable effect on utility bills.  A building with positive inside pressure will have less air infiltration, so while you are heating cold air, it may help in other ways.

A HRV is what you need.  You may also be able to fit gravity back draft dampers in the ducts, although I do not know if code permits dampers on for the make up air.

Bruce

As Bruce said that is for makeup air in the "furnace room". Our last house had that and it worked out great when we added an HRV. I just used one of them for incoming and one for outgoing. I ducted the output of the HRV to the fresh air intake on the furnace and just let the HRV suck air out of the "furnace" room. This will change that incoming air from -15F (like this morning) to something in the 30's. When we installed the HRV we had noticeable reduction in natural gas usage.

The other advantage is you can control the HRV to reduce humidity in the house. It was nice if you were cooking or having a party you could set it up on high speed and get more fresh air without the cold air blast from opening a window.

Thanks for the replies!

I'm not sure this is makeup air for the furnace.

Out of the back of the gas furnace, there are two PVC pipes to the outside. One is obviously exhaust (you can see the vapor outside) and I think the other is air intake there appears to be a small amount of suction on the open end of this pipe outside and if you feel both PVC pipes in the furnace room, one is warm and the other is cold (intake and exhaust).

I think I need to research HRV and the associated costs and payback.

Ian.

It sounds like you have a condensing furnace and if so, the PVC pipes are the flue and make up air as you suspect.  You still need make up air for your water heater, however, if it is gas.

I remember seeing a rule (code?) that you need 1 square inch of vent area for every ????btu of the appliance.  If you google on combustion air, I suspect you will find the rule.  You may be able to reduce the area of your make up air intake with a damper or oriface plate.

Bruce

Yes it's a makeup air duct, in Wisconsin they didn't care if I had an electric water heater, dryer, range and direct vent furnace. They put the duct in anyway. They said if the next owner opted to go all gas then it was there, so they put them in every house no matter what appliances you choose. Maybe your local code is similar. Either way it is a good thing since you can now easily add an HRV.