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Installing a vent hood and would like to know about cold weather install

ChrisMax's picture

I'm installing a vent hood over our cooktop and the instuctions mention putting a thermal break in the line.  I've done a search and can't find anyone selling thermal breaks for 8 inch duct.  What can I use as a thermal break in an 8 inch round duct going up through the roof ?  The damper has to be installed on the cold side of the thermal break.  

Chris (post #207414, reply #1 of 4)

Never heard of it, never installed one but might know what it's talking about.

On several remodels, I've removed old piping or swapped out micro's for range hoods and found a rubber flexible boot between the round to rect. pipe and the rect pipe boot.  It was rectangular to fit, edged in slotted metal to slip on the ductwork. 

Had figured it was to make the final connection more "flexible" but see how it could be used to break a temp transfer in the piping.


Go or call an HVAC contractor that can fab ductwork if you're concerned.

I'm in NW Oh.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


Never heard of it either, and (post #207414, reply #2 of 4)

Never heard of it either, and I can't imagine how it would accomplish much in the way of protecting the in-line damper from cold temperatures since the primary source of cold will be the air within the pipe, not the pipe itself.

If you find an explanation for this, please get back with it. Maybe we'll learn something.

RE: Never heard (post #207414, reply #3 of 4)

I think the reasoning is that the damper would keep the cold air on the cold air side of the thermal break and the pipe would'n tranfer cold to the interior of the house.  That would have to one air tight damper though.

Thermal break in outlet pipe. (post #207414, reply #4 of 4)

A more interesting thing is, where does the makeup air come in?

This is going to be really cold, how do we get the makeup air into the kitchen withour freezing the cook?

Is it better to allow the cold air to enter over the hood, under or somewhere else, or do we rely on air being pulled in under and round doors and windows?

In a Passive house there is an in line heater to take the chill off the incoming cold air.