Need chimney advice for new installation of old wood stove

[mariposawrick]

This is a great site with so much information. I know there is a long thread about chimney problems, and I will read it. I think my concern is different.

I am working on installation of an old 1970's Sundance wood stove with one air control in front and below the 2 small doors, not a damper. It will be burning at 3000 feet altitude. I am installing a straight chimney,no angles. My attic space is 48 inches from ceiling joists to 4/12 roof. I will use 3 - 36 inch sections of triple wall
chimney to get chimney height above the roof and more than 2 feet over the roof ridge.

I can either go with a double wall stove pipe that is adjustable to fit the height from stove pipe collar to ceiling support box, no damper, or I can install a couple of sections of pipe with a damper somewhere in the 60 inches of pipe.

My main question is: damper or no damper? If so, then where in the 60 inches of stove pipe. I know i must have at least 6 inches below the ceiling from the top of the damper.

Thanks for all the good tips.

 

[begreen]

On an old stove I'd add a key damper to the flue pipe somewhere between 6 and 24" above the stove.

 

[mariposawrick]

Thank you so much, you are the only, therefore the best, reply I have had . . . Now I can actually order my pipe sections.

 

[mariposawrick]

Is it true that the higher in the pipe the better for a damper? So 24 inches above the stove collar is optimum, hypothetically?

 

[begreen]

I haven't heard that one before.

 

[mariposawrick]

What would be the criteria for placement?

 

[vasten]

My criteria is as close to where I can get in the event that I had to shut that damper down fast. I am not aware of there being a set height on a pipe damper. But because you will be adjusting it often you want it where it is comfortable for you to reach

 

[coaly]

You want it where it is comfortable to reach, normally in the first section of straight pipe.
It controls the chimney, which affects the stove.
Rising gasses in the chimney flue creates positive draft meaning a low pressure area in connector pipe and stove. The lowest pressure is at the stove collar. This low pressure is required to allow atmospheric air pressure to push into the stove intakes. Connector pipe, elbows, cap and screen all add resistance to flow or reduction of draft. The damper is a variable resistance added when the draft is too strong. So the higher in elevation, the less "push" you have into stove with lower air pressure so the more open it would need to be compared to the same system at sea level. Also weather conditions like high and low pressure areas moving over change the need for reducing or increasing draft. (open more for lower pressure) Every appliance has a requirement for a certain amount of draft measured in inches of water column, in your case measured at stove outlet. It can actually be tested like when setting an oil burner damper and is also set properly with a coal stove with barometric damper. It isn't that critical on a wood stove, so it is normally only tested when there are problems suspected. (faster movement of air through fire creates turbulence causing a better mix of oxygen with flammable gasses escaping wood. Firebox design and baffles inside require different demands of flow)
Closing the damper slows the velocity moving up flue which affects the stove by how much air moves through intakes. Placement is like a valve in a water line. It doesn't matter where the resistance is, it slows the flow. It doesn't "hold heat back". You'll notice the temp above damper stays the same until the stove responds by getting less air.

 

[mariposawrick]

Thanks all. I have now ordered 24 inch sections of pipe with plan to place damper between them. Total pipe to ceiling is 60 inches, total chimney from ceiling box to roof is 48 inches, chimney will be at least 36 inches above roofline to make it over 24 inches above ridge line. My other woodstove has an angle between stove and ceiling. It looks to me like the roof hole for chimney was made before the stove was purchased with its chimney line farther into the room. When I open the doors I pull the draft control open and it still has a tendency to smoke out a bit. If I add a damper in that setup should it assist in eliminating smoking or is it due to the angle that is already impeding draft?

 

[coaly]

When damper is open, the resistance is like it's not there. That allows free flow to eliminate smoke spillage. How could a damper assist in eliminating smoke? It only slows draft when closing, it doesn't increase draft.

Open pipe damper and open air intake allowing heat to rise into chimney. Open door slowly. Crack it, wait, then open fully. Fisher designed a latch that turned one direction to allow door to open slightly allowing flow to start and the second or two lag between turning latch the other direction prevented the problem of opening too fast. Air should then rush in eliminating smoke roll in.

What does "pull the draft control open" mean? Are you referring to the air intake? Or do you have another draft control like a top mounted damper??
Your stove is this model with spin type air dampers right?

(Same operation as a Mama Bear and considered a copy)

If it has a draft control on the back, that pulls open you wouldn't need another flue pipe damper.

One other bit about flue damper placement; Older dampers have metered holes in them. They were the right size for closing entirely for overnight burn or for the correct setting for coal stoves. Newer dampers have holes along the shaft. Some stove manufacturers supplied them with the stove for correct air flow through fire bed. (Chubby Stoves is a current example made to run fully closed with metered opening) Installing them high in the system allows the steel plate to run much cooler and soot sticks easily clogging the metered holes. The closer to stove, the cleaner the damper plate stays with a white powder instead of soot. No idea what you're talking about stating it must be 6 inches from ceiling.
If using double wall pipe, the short damper section went right on the flue collar when Dura-Vent chimney and pipe was supplied with Fisher Stoves.
When holes in damper are clogged, resistance is infinite instead of metered.

 

[mariposawrick]

Thanks Coaly, I get your input about the damper placement. My comment about 6 inches was in reference to the ceiling support box. It needs 2 plus inches of exposed box below the ceiling line. I am now planning to locate the damper in mid-pipe, between 2 24 inch sections of Duravent double wall pipe. My stove is an old early-1970's discontinued model made by a guy who called his company Sundance. It is a welded steel box with 2 seven inch doors, a fresh air intake below the firebox, about 6 inches wide, one inch tall, controlled b y a push rod. It will have a straight chimney, no angles. My other stove, already in place and working, is a more recent older model with double doors which name I cannot recall or look up now. It is located in another place. That stove smokes when I open the doors to load a log. But it has an angle in the stovepipe and only a control above the doors. I am not sure if that has any damper effect or purpose, or any fresh air intake function. I will follow your staqed opening procedure and see how it affects my situation. More to follow. Thanks