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Post by smokeout on Jan 7, 2018 15:25:23 GMT -8
Would someone mind to direct me to thread, to help me determine if my rocket stove is making enough extra heat to add a small bench?
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Post by coastalrocketeer on Jan 7, 2018 16:12:11 GMT -8
Would someone mind to direct me to thread, to help me determine if my rocket stove is making enough extra heat to add a small bench? I think the main indicator would be "what are my exhaust temps exiting the current heat scavenging portion of my heating device. Have to keep flue temps above 90 to avoid condensation. (Others will likely have additional info, considerations, and/or corrections to my statement above)
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Post by smokeout on Jan 7, 2018 16:32:27 GMT -8
Thanks coastalrocketeer, i have been experimenting with secondary air . At first I've been hesitant to try adding secondary air because I would see a temperature drop when I opened it slightly. I recorded the length of burn that I was getting with no secondary air. (Around 1-1/2 hrs) Because I'm running a feed magazine, my temperatures does fluctuate some. The heat exchanger was running around 900F . Normally leaving the heater was 180-200 F and leaving the shop going up the flue 100-120F.
I have now restricted the primary air really tight and opened secondary air all the way. I'm getting over two hours burn on the same amount of wood as before. The heat exchanger doesn't go as high . 850F is the highest so far. But the stove exit is over 250F and the flue pipe is 150F.
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Post by coastalrocketeer on Jan 7, 2018 17:50:45 GMT -8
I think Peter has stated elsewhere that you really have to measure chimney/exhaust temp at the center of gas flow, so your actual exhaust gas temp may be higher than 150.
I'm not sure about secondary and primary air and how that relates...
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Post by coastalrocketeer on Jan 7, 2018 17:53:49 GMT -8
The keys, I think are to avoid extracting so much heat that you kill the stack effect in your chimney, and or avoid condensation in the system...
Hopefully others will chime in about the subject because I am not experienced and just trying to share my understanding, which may well include misunderstanding or mistaken remembering of the statements of others on the subject.
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Post by DCish on Jan 7, 2018 18:41:19 GMT -8
I run a soapstone box stove followed by a dead end brick bench two bricks thick (about 6"). Internal dimensions are roughly 6 feet long by about 13 inches wide by about 18 inches tall. I measure temperatures constantly via three probe-type analog thermometers that show the temperature of the flue gasses at the center of the 6" pipe. I run the stove as close to the maximum rated temperatures as possible, which means that the gases entering the bench are usually between 600 and 700*F. With temps in the teens and single digits over the week before new years, I ran the stove constantly at that rate for days on end. Exit temps never got above 250 the entire time, and generally hovered closer to 200. Max bench-top temp was 160 (under 4 layers of wool blanket cushioning). On more normal winter days when the bench isn't totally saturated with heat, exit temps from the bench usually max out around 150-180 when I am burning about 3 batches a day (~freezing temps), and 120-150 on 2 batches a day (~40s temps outside).
I hope this is helpful. Sounds to me like you are already extracting most of the useful heat out of your system. Leaving a bit of heat to run the chimney isn't a bad thing in my mind. And keep in mind that temps at the bottom of the chimney, even an insulated one, will be warmer than at the top. Even if only the top end cools enough to give you condensate, you will still get condensate dripping back down the flue.
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Post by pinhead on Jan 8, 2018 5:54:17 GMT -8
When discussing temperatures, please let us know whether you're using the Celsius or Fahrenheit scale.
Do you burn your rocket stove on a regular (daily or more) basis? If so, you'll need to measure exhaust temps after the mass has been adequately heated to see if your system can handle more extraction. A tall, well-insulated chimney can handle slightly lower temperatures while maintaining draft. On the other hand, you don't want to run it too cool; condensation in the chimney can cause a stall.
160°F seems to be a pretty good "happy minimum" temperature for the exhaust if the chimney is fairly insulated. If you run the system from a cold-start very often (such as in the case of a "shop heater" that runs only on the weekends), you'll want to maintain higher exhaust temperatures (or include a bypass) to make the system easier to start.
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Post by smokeout on Jan 8, 2018 6:12:38 GMT -8
I run a soapstone box stove followed by a dead end brick bench two bricks thick (about 6"). Internal dimensions are roughly 6 feet long by about 13 inches wide by about 18 inches tall. I measure temperatures constantly via three probe-type analog thermometers that show the temperature of the flue gasses at the center of the 6" pipe. I run the stove as close to the maximum rated temperatures as possible, which means that the gases entering the bench are usually between 600 and 700*F. With temps in the teens and single digits over the week before new years, I ran the stove constantly at that rate for days on end. Exit temps never got above 250 the entire time, and generally hovered closer to 200. Max bench-top temp was 160 (under 4 layers of wool blanket cushioning). On more normal winter days when the bench isn't totally saturated with heat, exit temps from the bench usually max out around 150-180 when I am burning about 3 batches a day (~freezing temps), and 120-150 on 2 batches a day (~40s temps outside). I hope this is helpful. Sounds to me like you are already extracting most of the useful heat out of your system. Leaving a bit of heat to run the chimney isn't a bad thing in my mind. And keep in mind that temps at the bottom of the chimney, even an insulated one, will be warmer than at the top. Even if only the top end cools enough to give you condensate, you will still get condensate dripping back down the flue. Thanks DCish, I bet you really enjoy your soapstone heater. I have looked at those. They do make a beautiful stove.
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Post by DCish on Jan 8, 2018 16:54:55 GMT -8
Thanks DCish, I bet you really enjoy your soapstone heater. I have looked at those. They do make a beautiful stove. Thanks - it is a pretty stove, but I am constantly chafing that just when it gets up to a good, hot and clean temp, it is at or near the upper end of what it is rated to withstand. I am learning an awful lot by having the bench after it, but I can't wait until I get myself a rocket build to a level I am comfortable bringing inside. It is a good exercise in patience and incremental learning. Oh, and on the bypass idea that pinhead mentioned - there is absolutely no way I could start mine or add a log without one. That's probably contributed to significantly by the fact that the bench outlet is below the height of the floor of the firebox
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