Help with cold air coming in through bottom of gas direct ven fireplace.

[Agent0071]

Bought new construction colonial house 2007. It has a gas direct vent fireplace installed in a bump-out on the 1st floor in the living room. Cold air bellows in from the bottom vent in the winter. It is really bad. I looked in the basement and there is a cubby hole under it, and it does have insulation stuffed in it filling it up. It doesn't "feel" drafty there. I have no idea how the bump out is finished behind or above the fireplace or if the insulated/sheetrocked/draftblocked or anything. How can I go about insulating it better? What is the easiest way? It is all tiled around the fireplace to getting behind it from the inside would be a pain. Should I try it from the outside somehow by taking off the siding or something?

I haven't used the gas fireplace because the cold air infiltration is so bad when it is not turned on. I shut off the gas and covered over the insude with thick plastic. You can see the plastic "breathe" back and forth every time the wind picks up.

The builder of my house is no help as he went out of business...

 

[DAKSY]

This is the nature of this beast & the way they're installed.
For one thing, you've got a metal box - essentially sitting in
an unheated room - OUTSIDE of your house.
Even with NO cold air penetration from the outside, there
are natural, reverse-convection drafts, occurring.
Warm air enters the top of the firebox, gets chilled by the coldness
of the box & drops down the back & out the lower louvers,
creating the effect of a "draft."
If your contractor did not seal the doghouse, this effect is greater...
We caulk ALL the seams in the sheetrock & use aluminum tape to seal
the outer edges of the wall thimble.
We also wrap the DV pipe with tape insulation where it passes thru the thimble.
As a somewhat "bubble-gum & bailing-wire" quick fix,
you can use aluminum tape to seal EVERY seam & hole in the valve cavity...
Otherwise, like you said, you'll hafta get into the doghouse from the outside
& that can be a laborious task....

 

[Fsappo]

This is the nature of this beast & the way they're installed.
For one thing, you've got a metal box - essentially sitting in
an unheated room - OUTSIDE of your house.
Even with NO cold air penetration from the outside, there
are natural, reverse-convection drafts, occurring.
Warm air enters the top of the firebox, gets chilled by the coldness
of the box & drops down the back & out the lower louvers,
creating the effect of a "draft."
If your contractor did not seal the doghouse, this effect is greater...
We caulk ALL the seams in the sheetrock & use aluminum tape to seal
the outer edges of the wall thimble.
We also wrap the DV pipe with tape insulation where it passes thru the thimble.
As a somewhat "bubble-gum & bailing-wire" quick fix,
you can use aluminum tape to seal EVERY seam & hole in the valve cavity...
Otherwise, like you said, you'll hafta get into the doghouse from the outside
& that can be a laborious task....

Really couldnt have explained it better myself. Nature of the beast and would really require opening the wall and doing a reinstall for all intents and purposes.

 

[jtp10181]

First thing I would verify is if the glass is fully attached and secured.
Second, get a hold of snake camera if you can, or use a mirror. Looks through the hole the gas line comes in underneath and try and see the outside walls. They should be insulated AND sealed with drywall or plywood. If they are not, you basically have a hole in the side of your house behind the fireplace.