Stove Temps/FlueTemps

[bigblulbz]

Now into my second winter with the stove I have gotten fairly comfortable with my settings to get the stove to last overnight. One of the phenomena that I can get the stove to do is carry a hotter stove temp, say 450-500, than flue temp, 350-400. Now this is not at the end of a burn. This can be at anytime during the burn. To do this I typically have the door vents more open, 1/4" - 3/8", and the flue open only about 1/4. I love the heat output but have not experimented with how long the unit will burn like this. I was wondering at what flue temp will it slow down drawing air. When I do an overnight the vents are about 1/8" - 3/16" and the flue open a 1/4 also.

Just looking for a little feedback as to what others have found running their stoves like this.

Thank you.

 

[coaly]

That's what I get with a Mama connected to an insulated 6 inch Dura-Vent straight up single story chimney. The larger the flue and weaker the draft the more open it needs to be. I'm at 1000 ft above sea level.
Atmospheric air pressure drops the higher you go, so people out in the Rockies are going to run more open. Sort of like asking where everyone sets their carburetor adjustment trying to compare performance. Variable change and so does the adjustment.
Remember, the "draw" is actually the void created by warmer rising exhaust in the flue, and it takes atmospheric air pressure pushing down and in all directions to rush in to fill the void. So the differential temperature between inside and out of flue determines the difference in air pressure between the top of chimney and the air intake of the stove. Air density, (water molecules between oxygen reduces available oxygen at same setting) temperature, barometric pressure, mechanical fans reducing available pressure inside, and stack effect (air rising away from stove) are all factors that will change the "critical flue temperature" needed for enough differential pressure.
Try your stove on a 90 degree summer day to see how hot the inside of chimney flue needs to be for enough draft. Some stoves won't even stay burning.

 

[bigblulbz]

Understood. I'm at lea level, or pretty darn close to it. When I see this scenario playing out what is the proper corrective action? As I mentioned before the current set up is going away. Just trying to maximize burn times. Current setup goes from 6" single wall off the back to 7" Class A about 3' above there.

 

[coaly]

#1 Baffle in the stove. This will drop your flue temps directing more heat to the stove top. It's the simplest addition with the most results.
#2 6 inch liner if long term use. This would pay for itself in fuel saved over time. (and is required for most newer stoves)
With the increase of 1 inch in diameter flue size compared to outlet, you need to keep flue temp higher than if it were the same 6 inch diameter all the way up. (increase in size from 6 to 7 doesn't seem like much, but square inches across (28 to 38 square inches) is about 36% increase in size. The expanding hot gasses cool as they expand in the larger area, so the object is keeping above the needed 250* temp all the way up.
You should be able to achieve approximately 1/2 the stove top temp (600) of the flue temp (300 - 350) with a baffle and correct size insulated flue.

As far as longer burn times, closing air dampers down to a crack gives the longest burn, but also the lowest stack temperature. So you can only close them down so far and still maintain the 250* temp required at the top. (this is the decrease in efficiency = burn time having the larger flue)

 

[bigblulbz]

Thanks again. I had a baffle made out of scrap 516 stainless and never put it in. Procrastination at it's finest. Now, if I can just dig it out of my garage.