What is this vent by the furnace?

6 years ago

I've got some succulent plants growing under lights in my basement and was wondering why it is so cold in there. From my experience basements are 8 to 10 Celsius cooler that upstairs main floor, and that's fine, but am trying to get it a bit warmer down there without adding an oil heater.....

Anyway, there is this vent that is attached to the forced air furnace. It does not go into the furnace, it seems to be just externally attached, and feeds to the outside wall. At the bottom of this vent, the previous owner has stuffed polyester batting to this vent. I felt that part, and it is very cold, seems to be air coming directly from the outside. Whatever is this vent for, can anyone tell me?

Can I block it or just seal it off instead of using batting there? The vent is circled in red. Where the black arrow is just points to where the air filter goes in for the furnace.

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Comments (5)

fnmroberts
6 years ago
Yours looks like an older furnace. The “vent” is probably fresh air for combustion. That’s to prevent using interior air for combustion which has to be replaced and heated, would support the dryer too.

Newer, high-efficiency, furnaces have outside air directly into the firebox.
worthy
6 years ago
It is to prevent negative air pressure caused by furnace combustion, cooking and human respiration producing moisture, CO2 and other pollutants while the supply of fresh outside air may be limited. Even when using a high efficiency furnace, I was required as a builder to include such a duct, but was further required to supply a small heater to warm the incoming air.

I would hesitate to block the ducting as long as you have a conventional furnace--especially if there has been an effort to tightly seal the home.
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mike_home
6 years ago
Sorry, that vent has nothing to do with controlling or regulating air pressure.

It appears to have been installed to bring in combustion air for the furnace. It may not be necessary depending on the size of the furnace and basement. Do you know the size of the furnace (BTUs)? Are there any other gas burning appliances (water heater, dryer, etc.) in the basement? What is the approximate size of the basement area?
weedmeister
6 years ago
Because this looks like it goes directly into the return air box, I'm going to guess that it is a Make Up Air (MUA) vent for a exhaust ventilator fan over the kitchen stove, especially if it is gas. Cant see the other end, but there should be a damper in line, like barometric or electric. The pipe can be insulated. If this is a cold climate, an inline heater could be installed.
mike_home
6 years ago
It does not go into the return box. It is an open vent that is currently stuffed with insulation.