Chimney thimble block wall question

[WV_Wood_Chopper]

I received parts for my Class A 6" chimney which will be going up outside the house from the basement. I ordered a thimble but was noticing that it was 11" in diameter when my chimney pipe is 8" outside diameter. Can I just choose not to use a thimble and make a hole more like 8.5 - 9" in diameter? It is all concrete block 12" thick. Perhaps even line the inside of the hole with some sheet metal to protect the shiny class A pipe going through it? It seems the thimble is way oversized for going through block.

 

[NVHunter]

What brand is the pipe? Just curious as I'm about to have the same type of install completed.

Through 8" cinderblock wall in the daylight basement.

 

[begreen]

The thimble is to enforce clearances needed to combustibles. It's completely unnecessary going through a totally non-combustible wall like concrete block.

 

[WV_Wood_Chopper]

What brand is the pipe? Just curious as I'm about to have the same type of install completed.

Through 8" cinderblock wall in the daylight basement.

The brand is Shasta. It seems well made stuff.

 

[WV_Wood_Chopper]

The thimble is to enforce clearances needed to combustibles. It's completely unnecessary going through a totally non-combustible wall like concrete block.

Appreciate it. With That in mind I will probably make the hole just large enough to slide the pipe in and since the pipe ends are slightly bigger it will give me a little wiggle room. Then I can caulk it which will provide better insulation than that thimble. An 11" hole in concrete just seemed a bit much.

 

[WV_Wood_Chopper]

So today I used a hammer drill and 1/2 bit to make a 8.5" hole through the 12" block wall. I ended up making the hole through a center of one block so that the edges of the hole would not be cutting through solid block. I made holes in a circle then just drilled those same holes on angles to make a clean hole. Did that on both inside and outside. I bought some 8" black stove pipe single wall, cut it to 12" long and lined the hole then slid the chimney pipe through. I did that to help protect the chimney pipe. The chimney pipe had some play and was a little drafty and so I used some wood stove door gasket material to slide between the black pipe and the chimney pipe. That seemed to work good.

I have vinyl siding and used a tool to pull it open then placed a board under it where the support brackets screw into the wall. That kept the vinyl from collapsing.

I need another day to hopefully finish the chimney installation.

 

[begreen]

For best performance try to have a slight upward pitch of the pipe toward the tee.

 

[MattFoley772]

Chimney requires 2" clearance to combustibles. So an 8" OD would need a 12" diam. hole. A thimble ensures this clearance is met.

For non-combustible wall like concrete or cinder block you don't need 2" air space. As long as there is nothing combustible within 2" of your chimney you meet code. So your hole can be a hair over 8" diameter, no need for thimble. Just make sure you seal the outside wall of your hole to keep out wind and water.

 

[WV_Wood_Chopper]

Chimney requires 2" clearance to combustibles. So an 8" OD would need a 12" diam. hole. A thimble ensures this clearance is met.

For non-combustible wall like concrete or cinder block you don't need 2" air space. As long as there is nothing combustible within 2" of your chimney you meet code. So your hole can be a hair over 8" diameter, no need for thimble. Just make sure you seal the outside wall of your hole to keep out wind and water.

Chimney is all installed now except the final sealing around the opening. I have some high temperature caulk which should work. Inside I will use double wall stove pipe to keep my clearances to combustibles ok. Still have not decided on a good wood furnace.