Damper in double wall pipe
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I think bholler’s answer is the winner, at least short-term, a second damper! I should have thought of that.
@ED 3000, you might have the best long-term solution, but it would be a hired job. I stopped spending much time up on steep/high roofs a few years ago, when I decided that being paralyzed would cost me more than hiring a chimney installer or roofer. Even my chimney guy told me he was losing sleep over this job, in the days preceding my liner install. That roof scared him, and he’d spent nearly every working day of a 30+ year career on a roof. A 40 foot ladder does not even reach the top of that chimney.
In just three loads since yesterday afternoon, I’m learning a lot about the dynamics of this new rig. I’ll have some insight to post very soon, once I’ve been able to confirm my early observations.
@ED 3000, you might have the best long-term solution, but it would be a hired job. I stopped spending much time up on steep/high roofs a few years ago, when I decided that being paralyzed would cost me more than hiring a chimney installer or roofer. Even my chimney guy told me he was losing sleep over this job, in the days preceding my liner install. That roof scared him, and he’d spent nearly every working day of a 30+ year career on a roof. A 40 foot ladder does not even reach the top of that chimney.
In just three loads since yesterday afternoon, I’m learning a lot about the dynamics of this new rig. I’ll have some insight to post very soon, once I’ve been able to confirm my early observations.
Easy Livin’ 3000
Minister of Fire
Yep, no way I'd get on that roof without a lift. A fall off there probably doesn't result in paralysis...
Are there any other dampers available that accomplish bholler's suggestion without adding a second damper? If not available off the shelf, how could you modify the one to have smaller holes? I personally prefer the simplest solution to a problem, and while two might be the second simplest, the right one would be THE simplest.
Th dynamics of this system are interesting. A single, tighter damper would not be the same as two of these. Similarly, I find that I can't dial it down far enough when the cat is engaged and raging on full (per the owners manual), but at the same time, I need to open the damper before opening the door to prevent smoke roll-out.
I have a circuit equivalent for this system in mind, where the stove and damper are both resistors, and the height of the chimney the voltage potential. You can vary the value of the second resistor (damper), to make a higher voltage supply (chimney) push the same current thru the first resistor (stove). But as soon as you change the value of that first resistor (by opening the door on each system), they're no longer equalized by that second resistor (damper).
I have a circuit equivalent for this system in mind, where the stove and damper are both resistors, and the height of the chimney the voltage potential. You can vary the value of the second resistor (damper), to make a higher voltage supply (chimney) push the same current thru the first resistor (stove). But as soon as you change the value of that first resistor (by opening the door on each system), they're no longer equalized by that second resistor (damper).
Easy Livin’ 3000
Minister of Fire
Are fluid dynamics equivalent to electrodynamics? Or is it aerodynamics in the flue context? I'm all for creative thinking, but is this possibly "to a hammer, all problems look like a nail?" In disclaimer, as a physicist, I make one hell of a lumberjack.
There are equivalent circuits for modeling all systems, including those based in fluid dynamics. An oversimplification, yes... but this is a wood burning forum, not the Transactions of the APS.
Poindexter
Minister of Fire
I dunno man. My 15' stack probably pulls over 0.1" iwc at full throttle when outside ambient isnt even -20dF.
When i asked my local bk dealer a few years ago they didnt recommend more than 30 feet of vertical stack for any install- but seeing -40 dF every year and folks running wide open during that, well, i should have asked them months ago.
My current thinking is the 0.03 to 0.06 iwc draft measure is for medium low and medium high burns. Fwiw my copy of the bk manual does not specify under what operating conditions the draft should be measured.
When i asked my local bk dealer a few years ago they didnt recommend more than 30 feet of vertical stack for any install- but seeing -40 dF every year and folks running wide open during that, well, i should have asked them months ago.
My current thinking is the 0.03 to 0.06 iwc draft measure is for medium low and medium high burns. Fwiw my copy of the bk manual does not specify under what operating conditions the draft should be measured.
Easy Livin’ 3000
Minister of Fire
Is Transactions of the APS your recreational reading when not busy with the kids and/or firewood?
Seriously though, this is an interesting exploration of a problem that others probably have. Look forward to the outcome.
Imagine that you had an insert rather than the freestander. Fewer options would be available, particularly the two damper solution you're exploring.
Yes, I suspect you may be right. My open stack at 15 feet seems to pull harder than my tall stack with the damper dialed down to 0.08”, but this can also be deceiving.
This is to be measured on high burn, cat engaged, system at equilibrium. It’s spelled out in the Ashford manual.
This is oversimplified, but this is sort of what’s happening:
V1 represents the ideal 15 foot chimney, V2 represents a 30 foot stack. Vs is the drop across the stove, also measured as draft at flue collar. Rs represents the load of the stove, Rd the load of the damper. For a given value of Rs (a given stove setting), you can find a value of Rd that will make the 30 foot stack draw identically to a 15 foot stack. However, as soon as you dramatically change the value of Rs (eg. Open the loading door), you will need a different value of Rd (damper setting) to make the 30 foot stack perform properly.
In my case, setting the damper for close to 0.06” WC with the stove operating on high (per the manual) will always cause smoke spillage when the door is opened, if I don’t decrease Rd (open the damper) before opening the stove door.
Mine responds the same way, as far as the damper needing to be opened when loading..
I still have .10--.17 WC with one damper installed, I have a second one to install on top of the that one..
BTW, the OAK I installed a week or so ago has made a big difference in keeping the house at a neutral pressure, instead of a vacuum, thus retaining the heat much longer.
I bet if you found an old timer stone mason, he could get through that foundation of your's pretty easily !!
In my limited experience with stove shops, I’m confident in saying that I’m less easily confused than the average stove dealer.
This is where the thermostat might be causing problems. When does system equilibrium occur? For quite some time after cranking up the stat to 100% the flapper is very open but as firebox temps approach the maximum, the flapper closes. It seems to overshoot and cycle a few times before settling into a steady flapper position. To achieve equilibrium at max output will take quite a while.
Easy Livin’ 3000
Minister of Fire
I think the actual variability in measured value is really much less than you’re expecting. Load stove, get up to temperature, close bypass and let ‘er rip on high for 30 minutes... all SOP, per the manual. Then check your draft. If the damper is still throttling a bit at that point, it should be by very small amounts, and is not going to make much difference in the draft measurement.
There’s nothing wrong with your theory, it’s just it doesn’t translate into enough difference in the actual measurement, at least on my stove. I don’t really seem to have my flapper oscillating closed on a high setting, but maybe the Princess design is different, or your thermostat is out of whack.
30 minutes is nothing. You haven’t reached high temperature yet. Certainly not equilibrium. Leave that sucker on max for two hours and you should be near equilibrium. Flue temps will have fallen some as the flapper closes to maintain that high temp and not just to reach it. Lower flue temps should mean falling draft strength.
Maybe you’re right, but then again, how much is the measured value really going to shift? If we get another cold spell, I’ll try this and find out, but I will be surprised if the draft really peaks much higher after the first 30 minutes.
All the more reason not to put this in the owner manual. Same reason why the cat thermometer no longer has any temp markings.
Easy to try. I’ve been really surprised at how the stove goes from a raging inferno during acceleration to a very mild looking fire once cruising at the set point. Also interesting is that the flapper will be more open to maintain setpoint temperature with a few large splits than it will with a firebox full of twigs.
Different flapper settings and flue temperatures will have an effect on draft strength.
With your permanent manometer installation you get to test out all kinds of theories.
Poindexter
Minister of Fire
It would be really interesting, i think, if we could visit each others homes and operate each others stoves.
At 30 minutes post engaged cat i have a raging stove, highly active cat, zooming fans and the steam in my plume has settled down.
Ill try to quantify tomorrow where between 20-30 minutes my steam plume settles down. When i was running fuel under 11% last year, the free water was boiled out in under 20 minutes. At 14% this year, ill go with the 24-26 minute window as a swag, but outdoor temp makes a difference for me.
I do think @Highbeam has a good point about split size v- acceleration from cold start.
At 30 minutes post engaged cat i have a raging stove, highly active cat, zooming fans and the steam in my plume has settled down.
Ill try to quantify tomorrow where between 20-30 minutes my steam plume settles down. When i was running fuel under 11% last year, the free water was boiled out in under 20 minutes. At 14% this year, ill go with the 24-26 minute window as a swag, but outdoor temp makes a difference for me.
I do think @Highbeam has a good point about split size v- acceleration from cold start.
“Honey, I have to go to Alaska.”
“For work? You guys don’t have an office in Alaska.”
“No, I’m going to go run Poindexter’s wood stove for a few days.”
“The kids and I are leaving.”
Have you checked your draft? Mine’s holding 0.08” WC on high at 30 minutes, and it never “rages”, anymore.
What’s interesting, and I’m trying to decide if it’s real or just my imagination, is that it seems the house is holding heat better with the damper installed. Is it possible this enormous chimney was really pulling that much more air thru the controlled inlet of the stove, when my draft was 2x higher?
Yes, I know... I need an OAK.
Good news. I always like to see a damper on a >30' flue. I'm glad it's helping. What reading do you get after 30 minutes on low now?
I’ll have to answer that after I’ve had more chance to watch it. I get about .08” after 30 minutes on high, and that shoots up over 0.10” when I initially turn it down for an 8 - 12 hour burn (“medium” setting). A “low” setting would give me 30+ hour burn times, and I’m not likely to use that in the next few weeks!
I should set up a GoPro in time lapse, watching the Magnehelic.
I think it is more likely that your stove is mow putting out more heat because less is being sucked up the flue. Do you measure flue temps as well? I would bet your flue temps past the damper have dropped considerably. I know in my old house with 35' flue i could increase the stove top temp by quite a bit by using my stack damper. Without it to much heat was getting sucked up the flue
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