Sealing Chimney After Insert Install

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New Member
Apr 5, 2023
Vail (Tucson) Arizona
I'm reaching out for some help and advice after a less than stellar install of a Quadrafire SantaFe pellet stove. I'm not familiar with all of the proper naming or nomenclature, but I will do my best to describe the situation. I also drew a picture.

Before Install: My home was built in 2006 in Vail, south east of Tucson Arizona. The house was built with what I would consider a tin fireplace insert that was fueled by logs. There's a chimney behind the wall that extends above the rooftop equipped with a flu. It was challenging to get heat out of this fireplace as there was no air exchange at all and only radiant heat. We have tall 14' ceilings and heat pumps as the primary source of heat. We elected to purchase a pellet stove as a secondary heat source for the winter.

After Install: The flu was removed and much of the fireplace tin was simply cut and bent down or away to make a larger hole for the pellet insert. A piece of 4" corrugated flex pipe runs inside the original chimney from the chimney cap to the pellet stove and is directly connected to the exhaust of the stove. A hole was cut in the exterior of the house and fresh air pipe connected to the stove inlet. I thought between the air inlet and exhaust the stove was a closed system, but it's not. The fresh air pipe aims at the burn pot, but it's not sealed in any way. A large tin surround was placed around the stove to make the install look pretty and fill the gaps between the stove and the original fireplace opening. The surround somewhat sits flush with the original opening of the pellet stove, but it's not sealed either.

The Question: The exhaust pipe is just sitting within the original chimney pipe. There is a substantial gap between the two at the top of the chimney. There's obvious airflow allowed in and out of the chimney. I'm concerned there's substantial thermal loss happening here as I lose hot air in the winter and cold air in the summer. Sounds is another thing as it carries down the chimney pipe. Can I seal the top of the chimney? From a functional perspective, a storm collar seems appropriate as it would seal around the outside of the 4" exhaust pipe and I can use silicone and screws to seal and fasten the collar to the chimney top. This would effectively seal the top of the chimney and stop air flow. Is this ok to do? I asked my chimney sweep about it and he said not to do this as a convection draft is needed around the 4" pipe to prevent it from overheating when the stove is on.

The Picture: I did my best to draw the situation to illustrate what's going on. Yes, the flu is closed in the first picture when I should have drawn it open.

Apologies for the book. Thank you for your help!

Sealing Chimney After Insert Install
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When I put my chimney in I sealed the flue at the top and bottom. That I believe is code in my area. At the bottom I filled the area with rockwool insulation and a metal plate effectively blocking the flue from any up or downdraft. At the top I put a metal cover that seals the top water and air tight. No problems with any drafts. I have a Harman P43 not an insert. It sits outside of the wood burning factory unit. I covered the hearth opening with a metal cover that isn't airtight and I've never felt a draft. I also have a very good draft so I feel the exhaust is holding its temperature.
I would have fashioned a metal plate with a hole to fit the pellet vent, but which outer dimensions covered my chimney top. I'd have trimmed my stove with strips at the hearth ... or run the pellet vent through a plate behind my stove. If an insert, it too would have been sealed to my opening. The pellet vent is near 4" OD, but inside that is a 3" stainless steel liner, and air space too. The outer is galvanised steel then.