[jw138]

The chimney in my 1941 Minnesota home runs through the middle of the home from the basement to the roof. As can be seen above, the chimney chase was never sealed. Every room it passes through above the basement is finished so the only access to sealing the chase is from the unfinished basement.

It's perfectly acceptable if the basement ceiling is the only location the chase is sealed from, isn't it?

I recently put in a high efficiency furnace that's vented through the rim joist so the chimney is currently unused. That being the case, is it ok to seal the chase with Great Stuff Fireblock spray foam ? If not, is there any sort of fireproof spray foam that's legal for this purpose? What's not shown in the picture above are the other three sides of the chimney that would be nearly impossible to seal with strips of aluminum but probably doable with spray foam.

 

[Windows on Wash]

There are fire rated foams but I prefer sheet metal, intumescent caulk, and mineral wool insulation. Air seal is the more important factor.

 

[jw138]

There are fire rated foams but I prefer sheet metal, intumescent caulk, and mineral wool insulation. Air seal is the more important factor.

The more I read up on this the more I like your suggestion. Not just for this chimney chase issue, but for all air sealing tasks. It certainly makes seals easier to remove if ever needed and sheet metal is without question fire proof! Any tips and tricks for buying and working with sheet metal? Do the home centers sell lightweight sheets? Are tin snips all you need to cut with or will they leave cut pieces that won't lie flat? Any suggestions for bending without going to town and buying a brake?

 

[Windows on Wash]

Big box will have it in the amounts that you need it (you only need a little).

Snips are just fine and you can use a hammer and piece of wood to straighten up the edge if you need to.

They have hand bending tools at the big box stores or you can bend it across a piece of wood with a sharper edge (i.e. 1x4).

 

[jw138]

Big box will have it in the amounts that you need it (you only need a little).

So, there's two options at the big box stores; .025" sheet metal or HVAC ducting. The sheet metal is pretty heavy and looks hard to work with. The HVAC ducting is much lighter and looks far easier to work with. There shouldn't be any issue using the HVAC ducting, is there?

 

[Windows on Wash]

None whatsoever. Use that.

If you are worried, double it over.