Do I need a Flue Damper ??
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![[Hearth.com] Do I need a Flue Damper ??](/talk/data/attachments/172/172154-ce01a32f21f6083bc53965975cdcb508.jpg?hash=9iAr9FrezZ)
Welcome to the forum;
This was posted in the Fisher Forum, so I'll give you your own thread since it's not Fisher specific.
A flue damper is for controlling the chimney, which in turn affects the stove. Think of it as a throttle for the chimney.
Every stove requires a certain amount of draft created by chimney. The draft or rising hot gasses is what allows atmospheric air pressure to push air into the stove through the intakes. If the chimney flue is the same size as stove outlet and creates too much draft (very tall, or indoor chimney that stays hotter inside flue, or insulated that stays hot inside easily) you may need to decrease the draft with a damper. (A larger flue than stove outlet requires more heat since flue gasses cool as they expand, so the flow may not need to be slowed) The draft caused by chimney is decreased by the cap, screen at top if present, connector pipe diameter and length, Tee's or elbows and reducers. These all add resistance to the chimney, and a damper is a variable resistance to add more resistance when necessary. So no one can tell you where to run a damper or if it's needed without calculations that adds resistance in system and calculating the draft that will be created by chimney at a given temperature. The warmer it is outside, the more open it needs to be, the colder outside the more differential temperature from inside and outside flue and the stronger the draft, so you need to close it more. Weather conditions (high and low pressure areas) affect how much pressure you have pushing into stove, so the lower the pressure (also high altitude) the more open you need the damper. It actually affects the velocity rising up flue which in turn affects the stove by slowing the air coming in. Some (most?) know where to set it at a given time but many don't know why.
Flue dampers are required on double door stoves when burned with doors open and screen in place. The damper then becomes your only control to slow the fire. It's good to have one on any stove in case while loading you get a log stuck and can't shut the door right away while you fight it. By closing damper until smoke starts to roll in at top, then open slightly to allow smoke up you can slow the fire to make it more manageable.
You'll find when starting a fire with small kindling it may burn so fast it roars up the stack. Closing damper slowly until roar stops allows more heat to stay in stove to get the larger pieces burning. You could slow the kindling by decreasing air, but that is not to time to deprive the new fire of oxygen. This is providing you have the right size chimney that doesn't require an abnormal amount of heat.
Just remember to always open it fully before opening stove door.
This was posted in the Fisher Forum, so I'll give you your own thread since it's not Fisher specific.
A flue damper is for controlling the chimney, which in turn affects the stove. Think of it as a throttle for the chimney.
Every stove requires a certain amount of draft created by chimney. The draft or rising hot gasses is what allows atmospheric air pressure to push air into the stove through the intakes. If the chimney flue is the same size as stove outlet and creates too much draft (very tall, or indoor chimney that stays hotter inside flue, or insulated that stays hot inside easily) you may need to decrease the draft with a damper. (A larger flue than stove outlet requires more heat since flue gasses cool as they expand, so the flow may not need to be slowed) The draft caused by chimney is decreased by the cap, screen at top if present, connector pipe diameter and length, Tee's or elbows and reducers. These all add resistance to the chimney, and a damper is a variable resistance to add more resistance when necessary. So no one can tell you where to run a damper or if it's needed without calculations that adds resistance in system and calculating the draft that will be created by chimney at a given temperature. The warmer it is outside, the more open it needs to be, the colder outside the more differential temperature from inside and outside flue and the stronger the draft, so you need to close it more. Weather conditions (high and low pressure areas) affect how much pressure you have pushing into stove, so the lower the pressure (also high altitude) the more open you need the damper. It actually affects the velocity rising up flue which in turn affects the stove by slowing the air coming in. Some (most?) know where to set it at a given time but many don't know why.
Flue dampers are required on double door stoves when burned with doors open and screen in place. The damper then becomes your only control to slow the fire. It's good to have one on any stove in case while loading you get a log stuck and can't shut the door right away while you fight it. By closing damper until smoke starts to roll in at top, then open slightly to allow smoke up you can slow the fire to make it more manageable.
You'll find when starting a fire with small kindling it may burn so fast it roars up the stack. Closing damper slowly until roar stops allows more heat to stay in stove to get the larger pieces burning. You could slow the kindling by decreasing air, but that is not to time to deprive the new fire of oxygen. This is providing you have the right size chimney that doesn't require an abnormal amount of heat.
Just remember to always open it fully before opening stove door.
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I would put a damper in if this was my stove. Slowing down the burn in these old stoves reduces the heat going up the flue and gives it more residence time in the stove which translates to a hotter stove top and a bit less fuel burned.
This gives me questions. I am installing a 1970's Sundance stove with only one air control, and double doors. My stove collar is 6 inches, I plan using 6 inch double wall pipe approximately 62 inches to the ceiling support, then triple wall stainless 6 inch chimney pipe through the attic 48 inches from ceiling to roof, then 36 inches exterior chimney for the height requirement over roof and ridge. I am unfamiliar with this stove's burning characteristics but I know it was an effective home heater for over 30 years in a temperate climate. The stove will now be used at 3000 feet altitude, mainly during cold autumn and winter months. Do I need to install a damper in the stove pipe sections? From this article it sounds like placement higher in a tall pipe will enhance the burn, but my stovepipe/chimney height will be only 140 or so inches, so 12 feet. Also, do you recommend using fixed lengths or adjustable lengths for the stove pipe from stove to ceiling? Your opinions are appreciated.
A few extra facts. I plan a straight flue/chimney only, no angles. I do feel comfortable to burn with doors open, unless there is an advantage to be had radiating more heat into a room than through the small glass windows of the double doors. The original use of the stove was also at sea level, now it will be at moderate altitude in the foothills. Thanks
Put the damper at a convenient height above the stove. You will be opening and closing it with every reload.
Jay106n
Minister of Fire
I would. I ran my old AllNighter Moe last winter without a damper, I installed a key style in my flu pipe this year and it made a huge difference. Dampers don't cost much to get and and install, if you find you don't need it, just leave it open.
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Slocketman
Member
I <3 this topic, I was just thinking about the merits of installing a damper above the catalytic insert I'm going to have installed.
Would anyone know what type of damper would be good to get (maybe with a link to an online store?) to put on the bottom of an 8" flex liner?
The ones I came across with a quick search were the chimney top style dampers with a cable that drops all the way down through the chimney. Those don't seem like they'd be very easy to tell if you've got it set 20 or 60% open.
Maybe a damper that I could mount a foot or two above the insert and drill a hole through the bricks to run whatever type of control it has outside of the chimney where I can reach it?
Would anyone know what type of damper would be good to get (maybe with a link to an online store?) to put on the bottom of an 8" flex liner?
The ones I came across with a quick search were the chimney top style dampers with a cable that drops all the way down through the chimney. Those don't seem like they'd be very easy to tell if you've got it set 20 or 60% open.
Maybe a damper that I could mount a foot or two above the insert and drill a hole through the bricks to run whatever type of control it has outside of the chimney where I can reach it?
Dampers are not made or meant for flex liners. Normally they are not tough enough nor rigid enough for the frequent setting of the damper.
Slocketman
Member
Hm, I was hoping there might be one designed for flex liner somehow.
Do you think if might work with a short section of rigid attached to the stove exhaust with the damper on top of that, then the flex liner?
At the moment I'm leaning towards using a 316 alloy heavy wall flex liner, but if it would get too hot at the point right after the damper when partly closed then that's a no-go, don't want it to shorten the lifespan.
I'd love to go with a 316Ti heavy wall flex but they're just way too much $$$$.
Or would the benefits of the damper be negated by the cons of having all those extra joints that can leak?
Do you think if might work with a short section of rigid attached to the stove exhaust with the damper on top of that, then the flex liner?
At the moment I'm leaning towards using a 316 alloy heavy wall flex liner, but if it would get too hot at the point right after the damper when partly closed then that's a no-go, don't want it to shorten the lifespan.
I'd love to go with a 316Ti heavy wall flex but they're just way too much $$$$.
Or would the benefits of the damper be negated by the cons of having all those extra joints that can leak?
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