I have a woodstove with a 6' top flue opening. Can I connect it to 8' stovepipe with an adaptor and get good performance? Total length about 15 '. Tested outside with 6' of pipe but was fairly smoky with doors open.
6" to 8"
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Is this straight up or up to an elbow and out to a chimney? What make and model stove is this for?
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Performance and efficiency is much better with the same size pipe and flue all the way.
The object is keeping the internal flue gas temp above 250* f to the top when smoke is present. This is easiest achieved by an insulated 6 inch flue.
The reason is below 250*, water vapor from combustion condenses on the chimney flue walls allowing smoke particles to stick, forming creosote. When exhaust gasses are allowed to expand, they cool considerably. 6 to 8 is almost double the internal square inch. This cools by almost 1/2. So running a stove efficiently with less wasted heat up the stack with 8 inch, requires about twice as much heat to be left up with thr larger diameter chimney.
A surface thermometer on the pipe exterior surface reads about 1/2 the internal flue gas temp. So reading 250 on the thermometer is approximately 500 internal. Cooling by the time it reaches the top can be down near 250, (depending on interior / exterior, masonry or insulated flue chimney) hence the cool range on thermometer at about 250. With a larger pipe and flue you would need to run the stack hotter, wasting fuel. It’s a guess what the actual temp is at the top without an IR thermometer to check.
Outside with pipe on the stove you don’t have a flue hotter inside than the outdoor temperature. This is what creates a low pressure area in the stove allowing atmospheric air pressure to push into the stove. So you end up without enough oxygen to make it burn clean without smoke.
The object is keeping the internal flue gas temp above 250* f to the top when smoke is present. This is easiest achieved by an insulated 6 inch flue.
The reason is below 250*, water vapor from combustion condenses on the chimney flue walls allowing smoke particles to stick, forming creosote. When exhaust gasses are allowed to expand, they cool considerably. 6 to 8 is almost double the internal square inch. This cools by almost 1/2. So running a stove efficiently with less wasted heat up the stack with 8 inch, requires about twice as much heat to be left up with thr larger diameter chimney.
A surface thermometer on the pipe exterior surface reads about 1/2 the internal flue gas temp. So reading 250 on the thermometer is approximately 500 internal. Cooling by the time it reaches the top can be down near 250, (depending on interior / exterior, masonry or insulated flue chimney) hence the cool range on thermometer at about 250. With a larger pipe and flue you would need to run the stack hotter, wasting fuel. It’s a guess what the actual temp is at the top without an IR thermometer to check.
Outside with pipe on the stove you don’t have a flue hotter inside than the outdoor temperature. This is what creates a low pressure area in the stove allowing atmospheric air pressure to push into the stove. So you end up without enough oxygen to make it burn clean without smoke.
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