Hot Chimney

[opi89]

I recently had a one piece flexibile 6" stainless chimney liner installed, the chimney is made of old brick with no liner and is 12" by 12" inside. The installer used an 18 x 18" stainless cap which sealed the top of the chimney off. When i use the wood furnace the outside of the chimney (which is exposed in the house) gets very warm and i was afraid that the cap was not letting any internal heat escape. Should i be concerned?

Thanks for any help

[big johnson]

Can you measure your stack temp at the furnace before it enters the chimney? How warm is warm? Too hot to touch?

[opi89]

I didnt measure the stack temp. the outside of the chimney is not so hot that you cant touch it but is probably around 100 degrees.

[hearthman]

When relining for solid fuel, the liner must be listed to UL 1777 and installed in accordance with the listing. Since listings may be dependent upon either a zero clearance btw the liner and the inside wall of the chimney versus a one inch clearance AND either a zero or one inch clearance btw the outside of the masonry and combustibles, the only way to know which clearance is required is from a Level II inspection. If the inspection reveals the house framing, siding, and other combustibles are in direct contact with the outer masonry of the chimney, you must use the liner insulation required for a zero outer clearance. Since you have a 6inch liner in a 12x12, if centered, you will have a 1 inch clearance inside the flue. Regardless, ALL liners serving solid fuel MUST have some degree of insulation. If you have a wood furnace or stove connected to that liner and it is not insulated, call the installer back and demand he insulate it as it does not meet the IRC or NFPA 211.

FYI, UL 1777 tests a single brick chimney with the liner installed per the mfr. It is enclosed with 3/4" plywood painted flate black, lined with thermocouples in a 6" grid. The plywood is done at zero and 1" clearance to the outside of the brick. then they pump in 1,000Fx 16 hrs. If any one thermocouple plastered all over the chimney rises more than 90F above ambient room temp. the liner fails. Then, they escalate to 1,400Fx1 hr then cool to room temp. then they sock it to it 2,100F x 10 minutes, cool down, inspect and repeat for a total of 3x. If any one thermocouple rises more than 90F above ambient or the liner separates, buckles or is otherwise damaged, the liner fails. There is no way to pass this test without insulation.

You said an 18"sq "cap" on a 12x12 flue. Do you mean a 18" sq. "top plate" with storm collar and clamp or are you talking about a rain cap w/ mesh?

Hearthman

[opi89]

Ok, i recently had the pour in type insulation installed in my chimney, i took a reading on my outside chimney wall and the temperatures range from 100-130 degrees, is this normal?

[cmajerus]

never measured temp on my parent's when they burnt wood, but would not consider that out of line, flue temp is probably 400-600 when roaring, so that's a far cry from 100, now that it is a solid mass it may transfer a bit more temp to the wall, but the chances of dangerous creosote build up is lowered because the gap of cool air around your liner is gone.