Pipe damper

[DaveNY49]

Is a stove pipe damper a must for Fishers? If you don’t plan on using the screen? Or should they be installed either way? I’m hearing conflicting info. Some say a pipe damper for co telling heat and others say the baffle and draft knobs together control heat.


Thoughts?


Edit. Never mind. Saw an old thread where Coaly broke it down. I definitely do NOT need a damper with my set up. This can be deleted

 

[stoveliker]

D

Thread 'Flue damper'

Aug 28, 2024

Does the Fisher Teddy Bear require a pipe damper? I’m not finding info in the manual and I’ve been hearing conflicting things from people. Some say No, while others say YES. And some have said a flue damper is required for when using the stove with the screen on to watch the fire.


Any help?

• DaveNY49
• Replies: 9
• Forum: Fisher Stove Information, Parts, History and More

For completeness, this is for a 7 foot flue (!)

 

[DaveNY49]

D

Thread 'Flue damper'

Aug 28, 2024

Does the Fisher Teddy Bear require a pipe damper? I’m not finding info in the manual and I’ve been hearing conflicting things from people. Some say No, while others say YES. And some have said a flue damper is required for when using the stove with the screen on to watch the fire.


Any help?

• DaveNY49
• Replies: 9
• Forum: Fisher Stove Information, Parts, History and More

For completeness, this is for a 7 foot flue (!)

Yes correct. Actually closer to 8. I’m running my stoves solid with no damper. Currently my stove is at 600 with a stove pipe of less than 300 at the top before it goes to class A. Some folks are saying a. Damper will keep heat in but I’m not sure slowing down draft is good? I’m up for some education

 

[stoveliker]

The previous thread concluded with that a damper with these stoves is used to control draft, given the easy path of gaes and heat into the flue.
Slowing strong draft will then help slow gas flow, which allows for more heat to be extracted before it disappears up the flue.

My question is whether you have a draft that's suitable for cutting things down. Maybe it is, I don't know. 7-8 ft is short, so draft is lower than most installs.

This is what determines whether a flue damper is useful for this set up.

 

[DaveNY49]

The previous thread concluded with that a damper with these stoves is used to control draft, given the easy path of gaes and heat into the flue.
Slowing strong draft will then help slow gas flow, which allows for more heat to be extracted before it disappears up the flue.

My question is whether you have a draft that's suitable for cutting things down. Maybe it is, I don't know. 7-8 ft is short, so draft is lower than most installs.

This is what determines whether a flue damper is useful for this set up.

Great points. I have two stoves. A fisher teddy bear and a Bullard. The sealing on the doors and the draft wheels are tight! Yesterday I had my stoves at up to 600 degrees off the top of the stoves for a short time. (20 mins) and took measurements on the pipe. If the top was 600 the single wall was 375 and the class A was 110. But closing dampers completely then turning 1/4 open kept a steady 500 top (around an hour) with pipe in the high 200’s and the class A 95-100

I considered this good. You? I got 8 hour burns from both stoves.

 

[stoveliker]

375 on single wall equates to about 750 F inside. That's okay (not too high), but not very low. You're pushing a decent amount of heat up there.
So a damper then is good, as it decreased the heat flow (both in magnitude of the volume of gas flowing, and the resulting temperature of that gas).

Whether it is a good system or not, that depends; if you choked down the fire too much you will get a lot of gunk in the flue.
I don't know if the Bullard has secondary combustion (tubes with holes in the top below a baffle) or not.
You need to see nice flame, either primary on the wood (if no baffle and no secondary air, as in the fisher), or secondary near the top of the firebox (if a baffle is present, and secondary air tubes). If you don't see that, you're smoking the neighborhood out.

So, I consider it good if you slow down the fire (while still getting sufficient heat out, with a slightly cooler stove!) AND you don't see smoke from the pipe outside AND you still heat your home sufficiently for your comfort.

"good" here is "increased efficiency". In the end (hypothetical nonsensical example for illustration) maybe you could increase efficiency by 150% if you went down to stove top temp of 150 F (of course nonsense, but, but then you would not have enough heat for your home - so that's efficient but not good.

BTW measuring pipe temp on the outside of class A does not make sense. It's insulated.
(And don't drill a hole for a probe in class A either as it voids the warranty/UL listing = insurance agreement.)
So don't bother measuring the class A.

BTW, a burn time being good or not needs info on the volume of wood you got in there. What are the volumes of the fireboxes and did you stuff them full?

 

[DaveNY49]

Solid input. Thanks! The Bullard is bigger and both have baffles. I find the Bullard seems to work better. The baffle comes a little more than 3/4 across the top and it’s straight. Not curved which I’m finding works better than the angled ones.

I’m sure it’s not possible but I’d love to be able to run my stove at 500-600 degrees (especially in 0 weather winters here) for an extended time while keeping more heat in the stove. But I’m thinking a damper would block its ability to run hot. So, if I could have my stove temps that high and keep as much heat as possible from going up the stove that would be awesome. I’m thinking it’s not doable with my set ups.

The Bullard doesn’t have secondary burn tubes. Another person on here added some to his Bullard and honestly I’d be up for adding them to both my stoves. I was under the impression that they burn the smoke? But then I read some info where you have to see the fire and onky turn them on at an exact time and temp for so many mins and I don’t want more fickle tasks with my stove. I’d be up for showing you pics of everything but I’m sure by me telling you what I’m doing is enough.

But back to the damper. Some say add one for safety. To stop a chimney fire. Well, I burn good wood and clean my stack so I avoid fires. Some say I can keep more heat in the stove. Well, if that’s true I’m thinking I’d have to close the damper enough to where it’s then effecting my fire.

 

[stoveliker]

I don't know what is possible with your stoves.
A secondary system (tubes) will improve things, if designed well enough, meaning hotter stove top at lower gas throughput. But I don't know what temps are achievable.

Secondary air does require to dial down the stove. But it's not necessarily more fickle than dialing down an easy breather stove as yours. Too late and you risk runaway. Too early and you choke.
They burn whatever is not burnt in the primary fire. Smoke (=particles in gas), or half burnt gases (e g. CO and others). They produce heat near the top where the stove sheds well and can do so with a low amount of air (low gas flow).

Remember that efficiency has to do with how much gas goes up, and its temperature. Decreasing both and avoiding smoke (half or unburnt fuel!) is the holy Grail for efficiency.

I don't think flue dampers stop chimney fires. They do decrease the flow in the stove, allowing the gases to shed more heat into your room before rushing into the flue, and potentially allowing for more complete combustion, and thus lead to cleaner pipes , they decrease flame being sucked into flues due lower flow and path blockages, and decrease (not zero out) the air flow to a chimney fire if closed as much as it can be.

 

[coaly]

If your Fireplace Series double door stove is the unlisted version with angle iron corners, it is not a requirement to have a flue damper, but is needed for open door burning with screen in place.

If your double door stove is a UL Listed model a flue damper is required since it is required in the installation instructions in manual.

With screen in place, fire established, slowly close flue damper until smoke appears at top of door opening. Slowly open until smoke evacuates. This retains as much heat as possible, and is not considered a radiant heater in Fireplace Mode.

A flue damper has no insulating r-value. It is a variable resistance that slows the velocity of rising gases. The flue temperature is the same on both sides of it. It does not mysteriously hold the heat in the stove. It does slow the gases exiting, which slows air coming in. This affects the stove, by controlling chimney.

Every stove has a required draft measured at stove outlet. If you want to set draft, a draft gauge is needed. Since drafting constantly changing, you can only set it for an average. A barometric damper on a coal stove or oil furnace responds with atmospheric pressure changes both inside and outside of the home. They are not for use with wood, since the flap opens to let indoor air into flue, cooling and slowing the rising gases, reducing draft. In a chimney fire situation it opens to cool flue, but with the fire in the wrong side of damper, this feeds oxygen to the chimney fire, the opposite of what you want.

I only mention a barometric damper because you can see how often it changes to control draft precisely. Opening door to the outside, stove controls, wind, all makes it respond. So that shows how you can’t control draft very precisely manually.

Draft is a measurement of the rising gases in chimney, creating a low pressure area, or vacuum in flue, pipe and stove. This allows atmospheric air pressure to PUSH into intake, feeding fire oxygen. If you can control the fire with air intake only, this is good.

A older stove (mostly antiques) with no door gaskets and leaky seams requires a flue damper to slow the uncontrolled air leaks into stove. Burning wood, this causes it to burn too hot and fast. Burning coal, leaks into stove above the fire does not make it burn faster. Coal requires air to come up through it. So antique dampers were made with a metered opening when closed. This will reduce draft all the way down to .02 inches water column, and burn all night very steady. Wood stoves like your require more like .06, and stoves with higher resistance through firebox require .1 or more.

These are very very minute pressure changes. All less than your breath. Many factors such as outdoor air temperature, pipe configuration, insulated indoor or outdoor flue, altitude, atmospheric pressure, indoor air pressure, and fuel with different moisture content all affect draft and how much you need.

This is why you can’t go by what others experience is and how their system works compared to yours. Most people have been using stove controls for years and know how the stove responds, but don’t know why.

The basics are, the chimney lowers pressure, or creates draft. Everything else takes it away. There are formulas and rules to calculate what draft will be as well as what static draft should be for venting systems. Jay Shelton’s Woodburners Encyclopedia covers this very well.