Draft Stoping Around Heater Exhaust Duct
Jay20
| Posted in Energy, Heating & Insulation on
I have a 35 year old furnace and am not quite ready to give it up. The house is a two story with the furnace in the basement. The furnace exhaust flue goes up and out the roof on the second floor. The hole through the first floor sub floor is 1″ bigger than the flue. There are spacers centering the flue in the hole so there is a 1/2″ space around the flue. This is open all the way to the second floor attic. I can’t get into that attic. I have access to ceramic high temperature insulation that is used in our foundry at work. It can easily stand 800F with no issues. Can I use a small amount and put it around the furnace flue at the first floor sub floor as a draft stop. Thanks Jay
Replies
Exactly how much of a draft are you actually getting there?
If you have a 35 y.o. furnace, I'm guessing your house has other bigger issues to deal with.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
There are lots of issues. Trying to systematically go around and address them. Thanks for the advice. Jay
Single wall or double walled pipe? What kind of furnace...gas, oil, wood?
From a foundry I would expect materials that tolerate high heat, but not necessarily reduce the conduction of heat through that material.
The air space around the flue pipe is to prevent the surrounding materials from becoming hot enough to burn. If you wish to stop the air flow, the material used must be of high R-value and not combustable.
In most instances a 1/2" space around the flue could be called out as inadequate. More details would clarify what may be acceptable.
...............Iron Helix
Insulated flues generally require a clearance of 2" (or more, depending on the pipe) to combustables. The chase is usually sealed with a metal plate with a hole through the center for the flue pipe. The different mfgrs. of flue pipe all have units designed to allow their pipe to pass through walls, floors, ceilings, roofs, safely.
If it wuz me, and it ain't, I'd give up on that 35-yr old furnace. Give it a decent burial and get a direct vent HE unit. Multiple problems solved.
Mike Hennessy
Pittsburgh, PA
If you block that draft, there will be an increase everywhere to make up for it. My new direct vent hi eff gas furnace is so much better than the old converted coal furnace I had. It was 62 when I retired it. Much less drafts now because it sucks in its combustion air through a pipe from outside instead of through the building envelope.
Luckily I installed a make up air duct with a damper in it that opens when the furnace calls for heat about 15 years ago. I see this hole and know it is sucking warm air right up it. I don't want to create a fire hazard but do have ceramic insulation that would plug the hole at the sub floor level Thanks Jay
Best approach would be to cut two pieces of sheet-metal with U-shaped cutouts in them, and fit them around the flue, then caulk with furnace cement.
Probably the best approach. Thanks Jay