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Cold Basement Cause

fan in a can air make up

Cold Basement Cause Due To Furnace Make Up Air


On A Recent Post GreenMountainMan Asked…

“Great website Concord Carpenter!

As I awoke this morning to see the frost on my car’s windshield, it gave me a chilly reminder that I need to do a little insulating in my basement.  My basement is partially unfinished and I’d like to put some insulation between the exposed floor joists in the basement ceiling.

When I converted to gas heat last year, they put a fan in my basement that sucks in cold outside air and pumps it into my basement. Of course, it makes my basement cold, but it also makes the floors in a couple rooms on my first floor cold. That’s why I was thinking of insulating below the floorboards on the first floor.

Have you done a post on Cold Basement Cause, or could you?

Thanks! “

Fan In A Can

“Hey Green Mountain Man, 

What you have sounds like a “fan in a can.” They are a field control product that looks like a silver canister and is ducted outside.  It is designed to deliver make up air to your boiler.

For the proper operation and venting of gas or oil heating appliances, sufficient outside air must be supplied to the structure to make up for the air lost from venting heating appliances, fireplaces, clothes dryers, exhaust fans and other building air losses.

See pictures / diagrams below:

Insufficient Air Exchange

Insufficient combustion air can cause major problems for proper draft and operation of both gas and oil heating systems.

With new construction, standards for building insulation and energy efficient windows and doors have reduced the amount of air changes per hour. The combustion and make up air requirements in the codes are based on 1/2 air changes per hour.

Make sure that your system is wired to your boiler and that the fan only sucks in air only when the boiler is turned on. This is very important!

Adding Basement Ceiling Insulation

Adding 10″ of high density insulation will help keep the floors above warm and is an inexpensive do-it-yourself project. Use metal “spring wire” insulation rods to hold the insulation in place.
[bottom diagram]

Make sure you take the time to insulate up against the rim joist, which is the outer edge of house perimeter.

You mentioned that you have a partially unfinished basement which means you have some finished space.  Is that space heated? You might want to add heat to this area as well.

Install a programmable thermostat and set it to reset to the same low temperature every six hours. When you use the room turn up the heat and if you forget to lower the temp. it will reset in 6 hours.

While your at it this is a good time to evaluate and consider your basement wall insulation.


~ concord carpenter

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