Should I insulate the OAK duct?

MAD777

Member
Jul 6, 2016
101
New Hampshire
I'm building my home in New Hampshire with proposed corner installed woodstove on a, 16" high hearth. Pictured below is the OAK duct which will come in under the hearth. It will be inaccessible once the home is completed. On frosty mornings, which is nearly every morning throughout winter, there is practically ice formed on this duct. Note that the house is not currently heated and the concrete slab floor you see will have radiant heat in it.
The second picture is an artist rendition of the final product. My question is, should I wrap this duct in some form of insulation and if so, what material should I use?


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Rearscreen

Minister of Fire
Dec 21, 2014
645
Vermont
I get thin frost on mine but so little it isn't a problem.
 

electrathon

Minister of Fire
Sep 17, 2015
523
Gresham, OR
Yes, two reasons. When not running it is a seal between inside and outside of nothing more than a piece of aluminum. When the stove is running the cold air coming in (and drawing heat out of the room to go into the air inlet) will condense moisture on the tube possibly causing water damage in the long run. I can not think of any valid reason not to insulate it.
 

jetsam

Minister of Fire
Dec 12, 2015
4,229
Long Island, NY
youtu.be
I'd insulate it to prevent the water in the house from condensing on it.

Limiting airflow around the duct will also limit the amount of condensation, so a simple box o' bricks could help a lot.
 
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zrock

Minister of Fire
Dec 2, 2017
716
bc
You could wrap with fiberglass pipe wrap. Or fill the void in the hearth with rocksol or how ever you spell that.. its fireproof insulation...

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Bartman23

New Member
Jan 26, 2019
18
Manitoba canada
I do mechanical insulation for a living. If theres gonna be any bend to it a piece of 2" thick flexible duct wrap sealed with foil tape would be your easiest option. Just dont pull it super tight and ensure your tape is rubbed down so it doesnt let go over time. Armaflex is also another good product for cold applications
 

electrathon

Minister of Fire
Sep 17, 2015
523
Gresham, OR
Not sure I understand. Not insulating will promote more condensation. Condensation leads to mold. Not sure why that is desirable.
 

Bad LP

Minister of Fire
Nov 28, 2014
879
Northern Maine
Insulate.
 

Rearscreen

Minister of Fire
Dec 21, 2014
645
Vermont
Well, if you were to use fiberglass insulation, eventually mold could occur. A closed foam surround not so. One question, how far above the ground does your pipe terminate outside?
 

Ludlow

Minister of Fire
Jun 4, 2018
1,084
PA
I insulated mine. Used fiberglass. Mine is exposed and straight out the back.
 

Highbeam

Minister of Fire
Dec 28, 2006
16,267
Mt. Rainier Foothills, WA
Rip that thing out and use actual metal duct inside the hearth. Its cheap, easy to insulate, and you won’t have to worry about replacing it like you would that silly flex line when some person or animal steps on the exposed chunk that is above your finished hearth. Only use flex above the finished floor between the duct snout and the stove.

Since this duct is under the finished hearth, the insulation can be combustible. Anything.
 
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MAD777

Member
Jul 6, 2016
101
New Hampshire
What’s all the black on the floor?
It's gone today. I took the picture last week after we were having negative temperatures for several nights and teens for daytime highs. The spot is gone now. The last couple of days have been in the 50's with overnight above freezing. I suspect the discoloration was due to melted frost, actually a layer of ice, that I observed on the duct last week.

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