Insulation Near Double Wall Chimney

[jerrodlk]

Hello,
We are installing a zero clearance fireplace in standard 2x4 construction house. The contractor packed batt fiberglass insulation directly onto the fireplace between the 2x4s. It touches the fireplace but not the double wall pipe. We are getting ready for sheet rock now.

Should the insulation touch the fireplace at all? Should I make a plywood barrier between the chimney pipe and insulation?

Superior WRT4536 fireplace and 12D double wall chimney pipe

Thanks,

 

[begreen]

It looks like there is supposed to be a 1.5" air space on the sides and back of the fireplace. Did the contractor use 6" batts for 3 1/2" cavity? If so, switch to 3 1/2" batts. I would prefer Roxul to fiberglass here. I wouldn't cover the batt fiberglass with plywood.

Pics always help us to see what you are concerned about.

 

[jerrodlk]

It looks like there is supposed to be a 1.5" air space on the sides and back of the fireplace. Did the contractor use 6" batts for 3 1/2" cavity? If so, switch to 3 1/2" batts. I would prefer Roxul to fiberglass here. I wouldn't cover the batt fiberglass with plywood.

Pics always help us to see what you are concerned about.

Looks like its 3 1/2" thick batt but it is open to the chimney pipe. Is it ok for the batt to be open to the chimney pipe inside the chase?

 

[begreen]

Yes, as long as it is secured in the stud bay in some fashion. You don't want the batts flopping out over time.

 

[jerrodlk]

Yes, as long as it is secured in the stud bay in some fashion. You don't want the batts flopping out over time.

I was going to put plywood behind the batts in the stud bay to keep it from falling out onto the fireplace or chimney pipe. What other method should i use?

 

[begreen]

Normally the batts are secured with criss-crossed wire over them or drywall. A good staple gun can make quick work of this.

 

[jerrodlk]

Normally the batts are secured with criss-crossed wire over them or drywall.

I am not talking about insulation in the back of the chimney chase. It is between the chimney and the room.

 

[jerrodlk]

Like if you tear off the mantel, then tear off the drywall, then there is batt insulation, then there is a chimney pipe. This seems like the chimney pipe will heat up the batt and cause a problem.

 

[jerrodlk]

I made the changes complete today. It was worse than I thought. The contractor had batt insulation packed around the fireplace and chimney pipe. The chase was also open to the attic. They were going to blow in insulation into the attic and of course right into the chase.

I ripped out the batt insulation in the chase and installed plywood. I also put aluminum screening to cover the chase opening in the attic. Now there is no way for insulation to get into the chase or to touch the fireplace.

 

[jerrodlk]

Are you supposed to pack insulation around the fireplace unit?

 

[begreen]

I made the changes complete today. It was worse than I thought. The contractor had batt insulation packed around the fireplace and chimney pipe. The chase was also open to the attic. They were going to blow in insulation into the attic and of course right into the chase.

I ripped out the batt insulation in the chase and installed plywood. I also put aluminum screening to cover the chase opening in the attic. Now there is no way for insulation to get into the chase or to touch the fireplace.

There needs to be a fireblock in the chase at the room ceiling height. Not sure why you added the plywood, but it sounds like there are still issues here.

 

[jerrodlk]

There needs to be a fireblock in the chase at the room ceiling height. Not sure why you added the plywood, but it sounds like there are still issues here.

There is a fire block at ceiling height but how does the double wall pipe get air between the pipes if there is a fire block there


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[jerrodlk]

Previously the inside of the chase had plywood on 3 sides. The 4th side had batt insulation exposed to the chimney pipe.
Now there is now plywood on all 4 sides of the inside of the chase. Now the batt insulation is NOT exposed to the chimney pipe.


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[begreen]

There is a fire block at ceiling height but how does the double wall pipe get air between the pipes if there is a fire block there

Good question. By double-wall pipe I'm guessing you mean chimney pipe. At the ceiling height a fire-stop radiation shield is installed with an attic insulation shield on top.

 

[jerrodlk]

I understand the double wall chimney pipe draws between the two pipes to cool the inner pipe. I understand it draws air in from the bottom at the fireplace and expels it at the top of the pipe outside the home.
If the chase has a fire stop, it should be almost air tight below the fire stop. This is where the chimney draws air from. Then where will this air come from?


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[begreen]

I understand the double wall chimney pipe draws between the two pipes to cool the inner pipe. I understand it draws air in from the bottom at the fireplace and expels it at the top of the pipe outside the home.
If the chase has a fire stop, it should be almost air tight below the fire stop. This is where the chimney draws air from. Then where will this air come from?

From the air within the chase.

 

[jerrodlk]

That's the problem. The chase with a fire stop is air tight. It has almost no way to get air to feed the chimney pipe.


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