Sealed Gas Fireplace Clearances

[Mike Calcaterra]

We are going to do a fake wall build out and add stacked stone around our Marco direct vent sealed gas insert fireplace and install our TV over the mantel.  The house was built 20 years ago and for the entire time we have experienced a significant cold draft from around the fireplace during the winter.  I took this opportunity to remove the drywall and see what is going on behind the wall.  There appears to be a small gap at the bottom of the vent where it exits the house.  Was thinking I could use high temp caulk and seal the gap.   I also noticed that the drywall which was on the wall and butted up to the top of the unit had zero insulation behind it.  This would explain why the wall was always cold to the touch.  The Marco manual states that clearances are 0? on the bottom, sides, and back.  Given the original drywall extended down to the top of the unit I think I can add some type of rigid board that has an R value.  What product would work?

[Ken Amelin]

We are going to do a fake wall build out and add stacked stone around our Marco direct vent sealed gas insert fireplace and install our TV over the mantel.  The house was built 20 years ago and for the entire time we have experienced a significant cold draft from around the fireplace during the winter.  I took this opportunity to remove the drywall and see what is going on behind the wall.  There appears to be a small gap at the bottom of the vent where it exits the house.  Was thinking I could use high temp caulk and seal the gap.   I also noticed that the drywall which was on the wall and butted up to the top of the unit had zero insulation behind it.  This would explain why the wall was always cold to the touch.  The Marco manual states that clearances are 0? on the bottom, sides, and back.  Given the original drywall extended down to the top of the unit I think I can add some type of rigid board that has an R value.  What product would work?

If it is rated at zero clearance, then many types of insulation would work. Why not just use Batt Fiberglass for the walls. That may be your most cost effective solution. You may also want to look at sealing any air gaps to reduce any infiltration from the exterior. Look for clearance requirement for the direct vent where it passes through the outside wall. The manufacturer will have that information if not readily available.

[Bob Harper]

You have to refer to the mfrs. instructions. Since Marco is long gone, there is no factory support. Please eradicate that term "zero clearance" from everyone's lexicon. It has killed a lot of people. Factory built fireplaces are designed, tested and listed for stated clearances. Now, most are listed for a zero clearance to the floor. Some allow a zero clearance to drywall but not the studs. Some allow zero clearance to the studs but maintain clearances elsewhere around the box.

When you pack material, such as insulation, framing, drywall around a fireplace, you capture heat. Those clearances are to dissipate heat. You might burn your house down trying to deal with cold air infiltration.

The chase must be properly weatherized to the cold. Do that and you'll meet clearances and the code.

The unit must be properly installed. That includes the exterior firestop being caulked where permitted by the mfr. If the firestop is not properly caulked, yes, you can get cold air infiltration. Note, you cannot pack the cavity inside the firestop with insulation. Guaranteed fire.

Ensure the fireplace is operating properly with the glass properly installed.

Now, you have a very old fireplace you're looking to mess with. I'd junk it and replace it with a new unit, weatherize the chase with air sealing, rockwool batts covered with Thermo-ply with the seams taped with UL 181 foil tape, duct mastic or foam at clearances and caulk the pipe where permitted.

If you're still getting significant cold air infiltration, fix your house. Stop the upper level exfiltration then provide controlled low level infiltration elsewhere and the cold air will stop pouring through the fireplace.

[Lee A. Brammeier]

Please eradicate that term "zero clearance" from everyone's lexicon. It has killed a lot of people. Factory built fireplaces are designed, tested and listed for stated clearances. Now, most are listed for a zero clearance to the floor. Some allow a zero clearance to drywall but not the studs. Some allow zero clearance to the studs but maintain clearances elsewhere around the box.

When you pack material, such as insulation, framing, drywall around a fireplace, you capture heat. Those clearances are to dissipate heat. You might burn your house down trying to deal with cold air infiltration.

The chase must be properly weatherized to the cold. Do that and you'll meet clearances and the code.

The unit must be properly installed. That includes the exterior firestop being caulked where permitted by the mfr. If the firestop is not properly caulked, yes, you can get cold air infiltration. Note, you cannot pack the cavity inside the firestop with insulation. Guaranteed fire.

Ensure the fireplace is operating properly with the glass properly installed.

Now, you have a very old fireplace you're looking to mess with. I'd junk it and replace it with a new unit, weatherize the chase with air sealing, rockwool batts covered with Thermo-ply with the seams taped with UL 181 foil tape, duct mastic or foam at clearances and caulk the pipe where permitted.

If you're still getting significant cold air infiltration, fix your house. Stop the upper level exfiltration then provide controlled low level infiltration elsewhere and the cold air will stop pouring through the fireplace.[/QUOTE]




ditto