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Cold Air Pours In My Gas Fireplace

I have heard this so often from people who have this problem - cold air pours in my gas fireplace.

There can be only one reason - poorly-placed or inadequate insulation.

A lot of homes have the gas fireplace built into the wall and sticking out from the house.

The box is surrounded with siding and is approximately 4' x 5' in size.

The support underneath, in newer construction, is composed of some form of wood joist, typically an I-beam like the ones pictured to the left.

The protruding cavity MUST be completely filled with insulation, front to back, top to bottom, or cold air will flow into the gaps.  This cold air creates convective loops and will make its way into the house via small openings left by the gas line and fireplace materials.

In the subject house the underside in the basement was completely covered with drywall, so no visual analysis could be made of the insulation to determine the cause.  So, what to do?

This client had read some of my many thermal imaging blogs, and especially on this topic, and wanted a thermal image examination of the circumstance to give to his builder.  The house is two months old.


With the fireplace off Mighty Mo had a look see.

Looking at the fireplace with the camera, this palette uses orange and yellow to represent warmer temperatures and lavender, blue and purple to represent cooler temperatures.

The lower edge of the fireplace is very cold!

The surrounding area is 68F and the coldest spots are 46F!

Of course that cold can be felt coming in.  Outdoors at this moment the temperature is not that cold, about 30F.  Last week temperatures were much colder which was felt here, and precipitated the thinking about having a thermal image inspection.

Outside, again with the fireplace off, this is the view.

This is looking at heat escaping right at the floor level, which would be just under the fireplace. 

Radiant heat can be seen coming from underneath.

This is truly an insulation issue.

Then inside we turned on the fireplace and looked at the basement ceiling directly under the fireplace, covered with drywall.

The cold areas are obvious.

Convective looping (moving air) is happening as the fireplace warms up.

The cold is forced away from the fireplace, and here the drywall is probably 16" away.

So the solution is to remove the wood luaun panel on the underside of the fireplace box outdoors, and re-insulate the area properly, top to bottom, inside to outside.

And prevent air from being able to move inside that box!

Hopefully this will control the majority of the cold air felt in the family room!  And comfort is achieved.

My recommendation:  thermal imaging is a powerful tool and can evaluate things like this in a way that is not invasive and definitive.  The camera sees very long infrared wavelengths not visible to the human eye, measures temperatures, and organizes what it sees into an image.  Thermal patterns can be evaluated across surfaces evaluated to obtain meaningful data and interpretation.  And of course, all those interpreters, thermographers if you will, are really cute.  Give one a call!  You'll be glad you did.



Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


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