Do you need a dampener in a fisher Grandpa bear woodstove.

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Papabear alaska

New Member
Jan 1, 2024
Fairbanks Alaska
Hi everyone. I am new to this forum, and fairly new to wood stoves in general. I have lived in this house for 2 years and have a Fisher Grandpa bear stove with the 8-in hole in the back. Out of the hole in the rear is a reducer to 6 in that connects to a T with a cap on the bottom and then the pipe goes straight up out of the Second Story roof. Originally it did not have a T, but a 90° elbow. Last year I had a chimney fire, and I replaced the elbow with the T so that I can remove the cap on the bottom and run a chimney brush up for more frequent cleaning. My question is this stove never had a dampener installed in the stove pipe. I don't know if it's supposed to or not. I imagine it would make cleaning more difficult as I would have to take the pipe apart to clean it. I cannot get up on the roof to run the stove pipe down from the top especially not during the winter in Alaska. After reading some of the manuals for the stoves I think it may be too large of a stove for my cabin. It is approximately 950 to 1,000 ft and this stove is rated to heat up to 2000 square feet. I cannot leave the vents in the front open for very long before the fire starts getting out of control. In fact forgetting the vents were opened was what caused the chimney fire in conjunction with having burned a creosote sweeping log a day or two prior so that all the creosote that had come off collected in the elbow. Am I supposed to run the stove with events open for longer periods of time? Because now I am only really open them when I need to get the fire going again. But I have them closed the vast majority of the time. I would appreciate any advice and insight into my situation
Depending on which Grandpa you have, a flue damper is specified “as required” in the manual for Series III. This is for open door burning with spark screen in place.

It is not specified in the pre UL manual for Series I. But would be required using as a freestanding fireplace. Instructions below;

With fire established, screen in place, slowly close damper until smoke forms at top of door opening. Open slowly until smoke evacuates. This retains as much heat as possible while evacuating smoke. It is not considered a radiant heater in Fireplace Mode.

Keep flue damper open for closed door use.

Air intake dampers should control fire without flue damper.

The flue damper is a chimney control. It slows the velocity of rising exhaust gases, decreasing NET draft. Slowing down what goes out, slows what comes in. This may be needed for leaking door gaskets, or stoves with air leaks such as antiques without door seals or leaks between joints of cast iron pieces that do not seal.

Uncontrolled air leaks can be slowed with the flue damper.

The basics of stove operation is needed to understand how a flue damper works; Exhaust gases lighter than outdoor air rise in chimney flue causing a low pressure area in chimney flue, pipe, and stove. This allows atmospheric air pressure to PUSH into intake, or any other opening it can. This is pressure differential is measured as draft. The greater the temperature differential the greater the draft. Chimney height increases draft. Everything else, stove pipe inside, elbows, firebox resistance, all reduce draft. The intake opening is the highest resistance in the system.

You adjust air intakes using a thermometer on pipe.

The object is keeping flue temperature above 250*f to the top before exiting. Below this critical temperature, water vapor from combustion condenses on flue walls allowing smoke particles to stick. This forms creosote.

Open air intakes a few turns. Kindle fire, monitoring magnetic pipe thermometer placed at least 18 inches higher than stove on single wall pipe. Close air intake dampers down to about a turn and a half as thermometer comes up to 250*f. As temperature continues to rise, close farther to stay above 250*f while smoke is present.

Increase air as needed for more heat output. Do not burn while smoke is present below the creosote zone shown that should start about 250.

This is a guide only.

The surface thermometer reads about 1/2 the internal temperature. So 250* is about 500 internal. This assumes cooling back down to 250 at top, hence the 250 creosote zone.

Since all venting systems cool differently, this is only a guide. Check creosote formation frequently until you know how much you are forming.

Now you can see how important it is to size the stove to the area correctly. Burning a smaller fire in a larger stove may not be enough heat up a larger chimney designed for a larger stove.