Thread: Sleeved Flue

A little unusual today. They sleeved a clay flue with an 11" flex liner, then encased it in concrete. I tapped on the sides as far down as I can reach, and it seems solid. I can't decide 1) why they would do this, and 2) if it makes it unsafe. It does reduce the size of the flue, which could be an issue. The fireplace was pretty large and open, and maybe they were having trouble with it drafting back.

I'm not sure they even used the fireplace after this was done, as the flue was spotless. The other possibility is that there was a wood stove or WS insert in place that has been removed. The damper is still in place, though. The second photo is looking up through. It think that is insulation at the bottom to keep the concrete from flowing down through the opening around the flue.

Any ideas what was happening here? Haven't seen this one before.

Not sure what to make of the liner and method of installation but I don't like the flat shelf created where they stopped relining the flue.

Originally Posted by Nick Ostrowski

Not sure what to make of the liner and method of installation but I don't like the flat shelf created where they stopped relining the flue.

It's hard to see up in there, but I think that would be there either way. It would be the bottom of the 13" x 13" clay liner instead of the round 11". I was thinking later that maybe the clay liner was cracked, and this was a way of repairing it. There is no sign of a wood stove insert or stove at the house, and again, it doesn't look it was ever used.

They could have a smaller flue installed for a gas fireplace, with a metal crown at the top and a cap. That would fix it, I think.

I wouldn't want them to use it for wood-burning, put it that way. Too many mysteries there.

Don't they sometimes insert an inflatable sleeve in the flue, pump it up, and then pump cement or grout in the chimney before pulling the liner in the void?

I have seen this done with smooth stainless steel, but not with the flex. Weird.

Originally Posted by Gunnar Alquist

I have seen this done with smooth stainless steel, but not with the flex. Weird.

They filled in with the concrete as well?

The original Ventinox corrugated stainless steel chimney liner system was to drop the liner, fill with Thermix cementitious insulation 1" around the liner then install a mortar crown that slopes for drainage. There should be a listed rain cap installed on the liner itself or a 13"x13" traditional rain cap with mesh. If this was just for a woodstove, it would probably be ok. However, it appears they relined an open hearth fireplace with an 8" round liner. At a 12:1 ratio per code at a common 29" lintel height, that would allow for a fireplace 20" wide. Otherwise, this is severely undersized.

I agree with Bob.I have see this done with stove inserts .