I recently got my Baby Bear installed, I also added the "simple baffle" that Coaly came up with, but have only lit it a couple times. I'm wondering if I need or could benefit from a flue damper? Looking at the manual, no diagrams show a flue damper and it actually says not to add any additional dampers to the flue outlet. After letting it get up to temperature with air control open and then completely closing it for approx. 10 minutes, I have used an infrared thermometer on stove top and double wall stove pipe. With the front (lower) top 500 - 540 degrees, the back (upper) top reads 395 - 400 degrees and the double wall stove pipe is reading 220 -250 degrees at it's hottest spot 4" above the T attached to the stove flue. So my question is, should my stove pipe be cooler and would a damper cause it to be cooler and allow longer burn times? Thanks for any and all assistance.
Fisher Baby Bear should I install a flue damper
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Surface temperature readings on double-wall stove pipe are not very meaningful due to the insulating air layer. Install a probe thermometer about 20" above the flue collar for a more accurate reading of what is happening in the flue.
I read a couple places that flue gas temps are estimated to be twice as high as the surface reading on single wall pipe. With double wall pipe reducing the distance to combustibles over single wall from 18" to 6" manufactures have to have a rule of thumb.
The unknown safety margins in that determination make the actual temperature in your pipe unknowable if only the surface temperature us known.
I'm not looking for an exact temperature. I'm looking for a rule of thumb to help me decide if a flue damper would be useful for my stove. I assumed that distance to combustibles was based on a stove or a pipes surface temperature when being over fired for a period of time. Is that incorrect?
It will necessarily have to be, but that depends on the brand: design, metal and construction used etc.
If the UL testing report is available (I am not sure they are, and they for sure won't be free) for your brand pipe, then maybe you can find those data.
Simpler (and cheaper) is to buy a $30 flue probe thermometer from e.g. Condar.
If the UL testing report is available (I am not sure they are, and they for sure won't be free) for your brand pipe, then maybe you can find those data.
Simpler (and cheaper) is to buy a $30 flue probe thermometer from e.g. Condar.
At what temperature flue gas is a flue damper recommended. I have 7' double wall pipe changing to 4' class A chimney pipe as it goes through the roof.
I don't know the older stove you are using well.
But if you are more than a spike here or there running above 700F consistently, I'd consider that too much heat up the flue. (For modern stoves that number will be lower.)
But begreen may have a better answer to that.
Note that the pipe can handle much more - but you want the BTUs in the room not up the flue.
But if you are more than a spike here or there running above 700F consistently, I'd consider that too much heat up the flue. (For modern stoves that number will be lower.)
But begreen may have a better answer to that.
Note that the pipe can handle much more - but you want the BTUs in the room not up the flue.
I have no data on this. Double-wall stove pipe comes in different designs. The outer jackets of some are ventilated. I would imagine the distance from the stove top would also have a notable effect. It needs a probe in the flue gases to provide meaningful data. The probe thermometer will improve how one burns, even if there isn't a damper.
It's a protection to the stove and chimney pipe to keep it from repeatedly overheating the pipe. That's above about a 900º flue. It's an advantage at any point once the fire is burning well to reduce the amount of heat going up the flue as long as it is not smoldering the fire. Less heat wasted and the increased residence time of the flue gases in the firebox improves combustion.
Burnin Since 1991
Minister of Fire
What are the stovepipe brand and model names/numbers you are using?
And then there's this... Because a certain chimney pipe single or double wall is rated to a certain temperature doesn't mean you should run the temps that high. Those are just safety limits.
What we're looking at is efficiency. High temps in the stovepipe indicates you are losing heat out of the chimney that is not being radiated into the room.
If you want to know the internal temps of double wall stovepipe, use a probe thermometer.
I have an older stove. I have single wall pipe. I also have a damper installed to make my stove more efficient and it helps (Me) a lot in this situation.
Other considerations are the height of the chimney above the flu collar, bends in the pipe, flu/chimney pipe size and elevation.
I have a Fisher Baby Bear stove which has a 6" flue. Attached to the stove flue is a 6" Selkirk double wall tee ( model #DSP6TE-1). The flue goes straight up and through the roof with no bends. Attached to the tee is Selkirk double wall pipe (model #DSP6AL-1 and # DSP6P12-1). It is connected to 4' of supervent class A double wall vent pipe ( model #JSC6SA3 and #JSC6SA1) as it goes through the roof extending 3' above roof and 22" above roof line. I understand that flue gas temperature can't be determined by a surface temperature reading. I thought my readings of 220-250 degrees ( I have seen hotter) were pretty hot and a flue damper could be useful to me.
Burnin Since 1991
Minister of Fire
What is the total height of your chimney from stove collar to the cap at the top of the chimney pipe?
What is your elevation?
From the top of fthe flue collar to the cap where flue gasses exit is 23". Elevation of town where i live is 1050'. If it means anything, the top of my stainless class A is showing discoloration.
Burnin Since 1991
Minister of Fire
It's normal for the cap and last bit of pipe to get discolored. Post a pic if you think it might be a concern.
23 feet and you have one 90 degree bend ( The T pipe)
Including the 90 degree T and your elevation, the recommended height is 19.5 feet, so you are a few feet taller than the recommended, but not too bad. Your draft is probably a touch towards the high end. The exterior reading of the double wall pipe also seem high, though I can't find any real reference for the relationship of single wall and double wall exterior temps. I use single wall pipe and generally my exterior readings are generally 300-375 with the damper open and lower, 250-300 with the damper closed.
Double wall stove pipe dampers are different than single wall dampers. A single wall damper is installed manually into the pipe. A double wall damper is a pre-installed damper within a section of double wall pipe.
I usually recommend a damper. Worst case you won't need to use it too much, but I use mine daily. I think you will benefit from having one, but every setup is different and there is no "one size fits all".
Hope this helps.
Burnin Since 1991
Minister of Fire
I asked you how far it was from the collar of your stove to the very to where the cap was and you replied 23". Being the smart guy that I am I figured there is no way that it's 23 inches from the collar to the cap and figured you meant 23 feet.
If it's not 23 feet then how tall is it?
No, it’s not based on being over fired for a period of time.
Clearances are determined by the surface temperature of combustible materials to prevent pyrolysis. The benchmark temperature not exceeding 117°F above ambient air temperature.
Since a flue damper is a chimney control, the only way to know if you need it would be a draft measurement at stove outlet.
With your specs given, you would probably need one without a baffle plate added. Since a flue damper is a variable resistance that slows the velocity of rising gases up the flue, the baffle adds resistance in the firebox. So the opening size the exhaust gases pass through and angle of plate determines how much more damper you may need to slow exhaust gasses even more.
If door seal is clean and sealing well, you should be able to control fire with air dampers. The flue damper is for an over drafting chimney, which may be rectified with the correct size baffle.
I apologize, entirely my fault as I'm not up to speed on all the terminology.
10 1/2' from stove collar to flue gas exit at cap. 23" from flue collar to flue gas exit. I didn't know why the flue collar measurement mattered ( that's where my mind went when I read collar) but there's a lot I don't know. Sorry
10 1/2' from stove collar to flue gas exit at cap. 23" from flue collar to flue gas exit. I didn't know why the flue collar measurement mattered ( that's where my mind went when I read collar) but there's a lot I don't know. Sorry
Thanks for the correction on distance to combustables. I installed a baffle based on your "simple baffle". Sitting on the plate under the stove flue angling towards the lower top plate. After purchasing the stove I removed a rope gasket that had been added. The door seal area is clean. Is there a test to determine how well the door is sealing?
Go around the door with stove burning with shaken out match or incense stick to see if any smoke is drawn into stove.
You won’t have an overdraft issue with under 15 feet venting system height. There are other reasons to have a flue damper to consider.
Many stoves including this one physically work ok under 15 feet. That is normally the height used during testing, so is considered minimum height.
Baby Besr is the easiest model to flutter or chuff. They let you know when they don’t like the draft right away.
In the event of a chimney fire the flue damper is like an emergency brake. Also when starting, if you get a roar up the stack with too much kindling, tilting the flue damper until the roar stops is a quick way to keep the heat in the stove to preheat larger wood pieces instead of roaring up the stack.
It is easy to over use a flue damper by slowing draft, which slows oxygen coming in, slows velocity through firebox with less turbulence to mix oxygen with flammable gases. This all increases creosote formation.
I should have noted that all the surface temperatures I noted were with the baffle installed.
When testing with smoke being drawn in through the door, is there an acceptable amount or there should be absolutely none?
Are you aware of what the surface temperatures of double wall pipe are when determining the distance to combustables?
When testing with smoke being drawn in through the door, is there an acceptable amount or there should be absolutely none?
Are you aware of what the surface temperatures of double wall pipe are when determining the distance to combustables?
There should be little to no smoke drawn into door seal.
Double wall or close clearance connector pipe passes UL testing for 6 inches horizontal to combustibles. Single wall requires 18 inches, and the stove itself requires 36. No test temperatures given. But this is derived from 3 tests overfiring the stove hotter than you will ever get it.
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