BKVP
Minister of Fire
My first computer course in college involved punch cards. We thankfully upgraded to Fortran and then Cobol.
That's showing my age!
BKVP
Blazeking Ashford 30 install questions
- Thread starter kevk
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That's showing my age!
BKVP
Assuming you'll need 18' of stove pipe someone's math is a little off. He shouldn't be charging you any more labor to install double wall.
Just generally, you can get 48" sections of Selkirk dvl at home Depot for $160, or Walmart online for $120. So let's just say $150 (I pay about $110 for these). 4 sections is 16' and another 24" gives you your 18'. A 24" section is like $70. That's $670 in pipe minus the $100 that won't be spent on the single wall pipe.
You'll need a telescoping pipe in there, that was just a general figure. So I have no clue how he's coming up w that price.
Also your steep roof is going to require a decent amount of chimney pipe above your roof line depending on how far away from the ridge you are. You have to be 2' higher than any roof within 10'. If you're maybe another 7'+ out the roof you've got 25'+ of straight vertical run. I can't see you having any draft issues using single wall lol. But hey, we'll see if bkvp can chime in on that.
stoveliker
Minister of Fire
The point is not always draft issues. It's the cooling down of the gases, especially if the flue is tall. You want them to be above condensation at the cap to avoid build up in the pipe. The longer the travel the more it'll cool. So best to keep it warm and let the stove provide the heat as it is designed to do rather than the pipe.
On an Ashford 30 - 18' of stove pipe to 7'+ of class A, straight vertical run. Is it feasible to run double wall stove pipe? I couldn't imagine someone having draft issues on any stove using single wall with a pipe run like that. What's your opinion?
I definitely hear you. But on any pipe run you're going to have the most heat at the bottom and the top. I can pretty much guarantee you that cap gonna be blazing hot on a pipe run like that lol. Would the whole system stay a little cleaner with double wall? Probably a little bit but nothing significant. Ultimately it does all fall back on draft issues, that's pretty much the focus of what BKVP was talking about.
History and a few past threads where measurements were taken say this is incorrect. The draft will be strong, but so will the heat loss over the 18' if single-wall stove pipe is used. Considering the flue gases are coming out of the stove at around 350-400º, a 100-150º temp drop in the stovepipe will mean a chimney that gets gunked up pretty quickly.
BKVP
Minister of Fire
Feasible, yes. With existing installs with 6" single wall, we say go ahead and try. But be it known, you will likely need black double wall. For new installs, don't mess around and just go for the dbl wall.
BKVP
Well if he has to pay labor to tear it out and replace it, that's not very feasible for the homeowner. If he was doing it himself I'd say take the chance being that the single wall pipe itself would only run about $100.
Which part was incorrect? Measurements of what? Was the single wall stove pipe the only factor? What point in the chimney would you expect it to get gunked up the most?
BKVP
Minister of Fire
Begreen is 100% spot on. Each of us has our own experiences. We have tens of thousands of those experiences in my 25+ years. Caps get plugged, spark arrestor screens get plugged and chimney class A get excessive accumulation in a large number of installations with the most efficient stoves mfgs make today.
I'm in Alaska this week visiting retailers. Across the state they recommend double wall on installs. This is because it gets so cold, it exacerbates the effect of cold stack on performance, creosote accumulation and required sweeping to keep system clear of excessive build-up.
BKVP
stoveliker
Minister of Fire
The part where the temperature first drops below the condensation point. From that point up you'll see build up.
Given that gases will inevitably cool during their way up, longer flues need higher initial gas temps and/or better insulation to limit cool down in order to stay above the condensation temp.
Higher initial gas temps is where efficient stoves have a problem because their efficiency means they shed the heat into the room rather than pumping it up the flue. So their exhaust is cooler than less efficient stoves.
For a BK that is in particular an issue when running low and slow (as little heat is being produced, and thus little is available to keep the flue warm enough).
Hence for taller flues, it's advisable to use double wall, especially for stoves that can turn down very low.
I'd say the part where you say that you're going to have the most heat at the bottom AND the top. The latter is incorrect.
The laws of physics (thermodynamics, to be specific) dictate that in a heat exchanger (which your flue effectively is) heat transfer is in a linear proportion to temperature difference. And energy transferred leaves less energy behind. So most heat will be shed at the bottom of the flue where temperatures are highest (and the temperature difference to room temperature is greatest), and both temperatures and heat transfer will drop the higher you go.
Well guys this is all great info, particularly for the original poster to be able to make his decision which was my goal. Thank you.
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