Chimney pipe material advice?

[rickj]

Hi! Replacing old wood stove insert with new one. The new one needs a chimney pipe of 180mm, the existing galvanized pipe is 200mm. The manufacturer explicitly specifies 180mm, 200mm they consider too wide. You can use 150mm, but then your chimney needs to be 6 meters+, with 180mm 5 meters is sufficient, and I have that.

My idea is to insert a new 180mm pipe into the existing 200mm tube. The available material options are (too) plenty. There is galvanized iron, there is vitrified black pipe material, there is inox. All these are available as single-walled pipe material, but also double-walled. Then there are flexible (inox) liners, but a bit unsure if they survive sweeping.

The stove specs say flue gas temperature is 200°C/392°F; as I already have an existing metal channel, what sort of material would you recommend?
I like inox, but I have no idea if it is better for chimneys than other materials.
Double-walled could be overkill, as there already is an existing channel.
(Would you use spacers to nicely center the new pipe into the old one? )

 

[begreen]

Galvanized is pipe is not acceptable for a wood stove flue. It must be stainless steel.

 

[Joe Bruno]

Hi! Replacing old wood stove insert with new one. The new one needs a chimney pipe of 180mm, the existing galvanized pipe is 200mm. The manufacturer explicitly specifies 180mm, 200mm they consider too wide. You can use 150mm, but then your chimney needs to be 6 meters+, with 180mm 5 meters is sufficient, and I have that.

My idea is to insert a new 180mm pipe into the existing 200mm tube. The available material options are (too) plenty. There is galvanized iron, there is vitrified black pipe material, there is inox. All these are available as single-walled pipe material, but also double-walled. Then there are flexible (inox) liners, but a bit unsure if they survive sweeping.

The stove specs say flue gas temperature is 200°C/392°F; as I already have an existing metal channel, what sort of material would you recommend?
I like inox, but I have no idea if it is better for chimneys than other materials.
Double-walled could be overkill, as there already is an existing channel.
(Would you use spacers to nicely center the new pipe into the old one? )

View attachment 341199

Why not take the old galvanized out and start clean? As someone here noted, galv is not used on wood. I think it out gasses. I have never seen it used, so what you have must be quite old. Are you sure it is sound and not rusted?

As for inserting 180 into 200, it should fit if the run is straight, but double wall will add diameter and may not fit. You need to consider the OD, and the screws, if any, that attach one piece to another.

SS flex liners do fine with cleaning. Use a cleaning brush 1" smaller than the liner. Don't drip a chain as we used to do, that's too rough.

 

[rickj]

Why not take the old galvanized out and start clean? As someone here noted, galv is not used on wood. I think it out gasses. I have never seen it used, so what you have must be quite old. Are you sure it is sound and not rusted?

As for inserting 180 into 200, it should fit if the run is straight, but double wall will add diameter and may not fit. You need to consider the OD, and the screws, if any, that attach one piece to another.

SS flex liners do fine with cleaning. Use a cleaning brush 1" smaller than the liner. Don't drip a chain as we used to do, that's too rough.

The existing galvanized tube is 20 years old, the age of this house. Not in the US, but in Spain, so the rules may be different. I cleaned it with a rotating brush set, 550 grams soot and grit removed, it looks okay so far. Not rusted. Taking it out seems not necessary, as I'll use it as the outer wall from now on. And it's a lot of hassle to remove it! (The 20 cm tube is inside a masonry chimney)

I ordered lengths of 18 cm inox, single walled, and the clamps that connect the tubes, and a pack of Rockwool Firerock panels, to insulate the stove enclosure itself. I'll use strips of that material around the 18 cm tube as spacers. I prefer rigid tubes over a flex liner, it looks more solid, and it's cheaper too. Temperature rating of these tubes is 600ºC (1112ºF) without seal, 200ºC with flex seal inside the clamps. Will use without seal, then. Assuming those clamps will fit inside the 20 cm tube, will know in a few days! Else I will do some… engineering with a big hammer.

Double wall is available too, but I was advised it's not necessary, as the existing tube is a wall, too.

Will report progress/failure!