How much air should be supplied to the furnace from the outside?
parkerblendy
| Posted in General Discussion on
An unfinished basement and two floors above ground make up my 2600 square foot house. An air conditioning system with forced air was recently installed. Near the top of the furnace, there’s a duct connecting the cold air return duct to the outside. In response to my question, the installer said I should keep it. It does not make sense to me to supply the furnace with additional outside air, since it would increase the heating and cooling requirements. Can anyone please shed any light on the purpose of this duct and any reasons I should or should not remove it? BTW, my previous house in the same locality and of the same size had the same furnace but no outside duct. Thank you
Replies
My system has a dedicated inlet and outlet to supply combustion air and expel exhaust, I wonder if that is what he is saying it is necessary for. What does your exhaust venting look like? Also, that outside air into the return side may be an attempt to provide ventilation. But that would create a positive pressure inside and increase your air leakage.
This is a way to provide fresh air into the system.
In some cases, this makes sense, in others it does not.
I would want a way to shut it off in the winter. Your case should consider the location and climate.
You might get better answers from an energy audit which includes a leakage test on the house.
oil fired or gas fired furnace?
how "tight" is your house?
other fossil fuel burning equipment in the house?(gas fired water heater)?
If I understand your question and situation correctly, the fossil fuel fired furnace needs a required amount of "make up" air for combustion, otherwise, the furnace could cause a down draft from the other fuel burning devices and fill the house with exhaust (aka CO) gas therefore, the duct allowing air into the basement.
most houses used to leak enough that providing make up air unnecessary, however, newer houses and well insulated houses usually require make up air to prevent back drafting.
you could reach out to your mechanical inspector for advice on what's needed, or the local utility if they provide the fuel.
good luck