Furnace question

Snowmelt

True or false, furnaces like to draw back warm air, so someone told me not to take fresh air from outside just use it Fromm where it's heating, is that true or false?

rick in Alaska

I don't see what difference it would make to the furnace, except maybe really cold air. This would blend in with the rest of the returning air and temper it anyway. So can't see a problem.
And I am assuming you are not talking combustion air. I like to see it warmed up just for the better combustion it is capable of, but is just an unverified opinion.
Hope this helps,
Rick

Snowmelt

Not really, the problem is I don't feel like running another 25 feet of pvc to the outside wall and terminating it. At the same time I don't want to hurt the machine. I will do it if it's necessary but the question is it necessary ?

icesailor

Are you talking about combustion the air in the building that is being heated by the furnace?

Combustion air ends up balancing the inside pressure by being vented up the exhaust to the outside. If you draw room air from outside, some air, already in the building will have to leave. Air that you have already heated. You increase the overall Delta T of air through the furnace. Most buildings have more than enough air infiltration just on a regular day. If the idea is to have fresh air replaced in the building, they make air to air heat exchangers to take cold fresh air from outside and bring it in, while taking warm stale air from inside and exhausting it to the outside and extracting the heat from the exhausting air and giving it to the new incoming air.

Jamie Hall

Combustion air? Makes very little difference; the range of intake air temperatures is so small relative to the flame. But -- for maximum efficiency overall, ideally one would take outside air for combustion so as not to use the warm building. As has been said, though, most buildings have enough infiltration anyway to make no difference.

On the other hand, if you have a very tight building you can get into difficulty with not enough combustion air and, depending on the setup, some interesting draught problems or even recycling of the exhaust.

GW

I have always ran the two pipes. The second pipe is much faster since you already worked out the routing, your tools are out. plus you're allowed 12" instead

Edit, 12" instead of 4' from doors and windows

Tinman

I agree with Gary and Jaimie.

RobG

I guess the biggest question is did you RTFM?

Snowmelt

I did, said you really didn't need to it was optional

wogpa67

Is this for your house?