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Drafty Gas Fireplace Insert

Beeglowbot's picture

Hi all, first time on the FHB forum, couldn't find a search button so my apologies if this topic has already been covered.


We have a 2 story new construction spec home built in 2014, by a builder that's in it for the money, doesn't care about the craft. So there are glaring problems all around the house that show his attitude towards home building. One of the biggest problems (aside from the 2nd floor air handler being in the attic) is the gas fireplace insert.

It is set into an exterior chase that stops before it reaches the 2nd floor. There is such a draft from it that it feels like I've left a window open. I've tried covering up the exterior exhaust to no avail (we don't use it). Upon further investigation, I've noticed that there is nothing behind the insert, no insulation whatsoever. I see straight to the sheathing. The draft is also coming out of an outlet box above the mantle (because he assumed we were going to stick a TV above it and break my neck watching?) and from underneath the mantle surround. It appears the entire chase is uninsulated. My neighbor has the same exact spec home (they went up at the same time) and has the same exact problem. We called him and he told us this: "why do you need insulation, you have a fireplace right there, just turn it on". Yea...... I've done the best I can by caulking gaps and making a sealed cover for the entire insert, it's keeping the draft at bay but the floor and wall around the area are still cold. I eventually want yank the insert out and insulate that chase with rockwool (thinking Roxul Comfortbat). My questions are:

  1. Are there reasons why I should NOT be insulating the chase?
  2. Do I need to sheath the interior side of the chase to keep the insulation from touching the flue or is the rockwool good enough to ignore the heat since it's rated way beyond the flue temp.
  3. Is there anything else I should do while I'm in there?

Thanks in advance!

First you need to find the (post #214698, reply #1 of 3)

First you need to find the installation instructions for that particular insert (the manufacturer's web site should have this) and read up on clearances, required firestopping, etc.  (You may also want to contact your local building inspector re what local code requires.)

Then you need to make a plan which is doubly cautious with regard to fire hazards.  Eg, consider a layer of fire-resistant drywall, even if it isn't explicitly required.  Especially design in features that will eliminate the "chimney" effect of the chase.  If a fire does start you don't want it to easily spread upward.

Next, especially given that you will usually NOT be using the fireplace, you need to consider moisture migration issues.  Except fairly far south you have the problem that moisture migrates from inside the house to outside, and it can get caught between layers of the wall and condense/freeze, causing rot and other issues.  This is complicated by the fact that, if the insert requires a "clearance" to heat-sensitive surfaces, you can't directly place a plastic vapor barrier behind it but would have to have some other barrier (eg, the drywall) in-between.  Note that you SHOULD NOT place a vapor barrier behind your insulation (on the "cold" side) because this will trap moisture and make things worse.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Bee (post #214698, reply #2 of 3)

First thing to do is get the install and clearance specs for the fireplace company.  Study that and then attack the problem.

in addition, get underneath the chase and make sure that area is detailed.

best of luck.


edit: sorry for the repeat.

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

Remodeling Contractor just outside the Glass City.


Sealing the insert is going (post #214698, reply #3 of 3)

Sealing the insert is going at it the wrong way around. You need to pull the insert, get the chase insulated and air sealed, then put the insert back.

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.