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Post by mannytheseacow on Jan 28, 2014 7:21:30 GMT -8
Hello all,
I've got a 6" RMH (complete build over at Matt's site, "6" cast core thread"). Basic details: 6" cast core, ~23' of duct, ~3.5 ton mass bench heating a super insulated 2 story house with each story 750 ft2. The stove runs like a dream but it just doesn't have the output needed. If I feed it 24 hours a day it heats just fine but if I do a couple of fires a day it doesn't keep my house over 60o on days like this when the outside temps are -12o.
I'm planning to recast an 8" core and trench out the ducts to make them 8". I want this to be a one-time deal though. I don't want to do all this work and find an 8" can't keep my place warm either. I'm looking for some outside input here. Just switching to an 8" but keeping the same mass, is this going to be enough? Should I also include a bigger mass? I'm looking at mass temps 130-140o now and the barrel easily runs 600o+.
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Post by pinhead on Jan 28, 2014 7:34:37 GMT -8
An 8-inch stove is almost twice the CSA and heat when compared to a 6-inch system (1.77 times to be exact).
I believe a 6-inch Peterberg Batch Box may be able to run on a 6-inch bench - and put out much more than double the heat.
What is the temperature at the base of the chimney in your current system?
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Post by mannytheseacow on Jan 28, 2014 7:59:41 GMT -8
I've been looking at the batchbox design but I haven't found any clear info on building one the way the Walker cast-core does (read: basic how to for dummies) so I'm kind of in the dark about the batch box yet (read: i'm a dummy). I really like the even heat of the cast J, and also emissions are a factor in my choice. Peter's comments about batch boxs not being as efficient as the J have kept me steered towards the cast J.
I don't have a way of measuring interior temps in the output flue, but the pipe where it meets the masonry chimney is reading about 120* on the exterior, and that's which a good heated mass.
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Post by pinhead on Jan 28, 2014 9:42:59 GMT -8
I've been looking at the batchbox design but I haven't found any clear info on building one the way the Walker cast-core does (read: basic how to for dummies) so I'm kind of in the dark about the batch box yet (read: i'm a dummy). I really like the even heat of the cast J, and also emissions are a factor in my choice. Peter's comments about batch boxs not being as efficient as the J have kept me steered towards the cast J. You must have misunderstood. First, the batch rocket is more or less on a par with the unaltered J-tube combustion efficiency-wise. The optimized J-tube is slightly better, by a relative small margin only. The crux of the batch rocket is this: it is able to run with very low excess air, much lower as compared to the J-tube configuration, coming very close to complete combustion at the same time. The exhaust temperature is often higher, yes, but that's only logical. Due to low excess air the temperature of the burn will rise and so is the exhaust. That doesn't mean the overall efficiency of the J-tube is higher. The RMH is another beast, capable of very low exhaust temperatures but excess air is generally high. Thermal efficiency is wholly dependent on your heat exchange arrangement and optimization and therefore has very little to do with the stove itself (assuming it is burning cleanly). The batch box consumes much less excess air which gives it an advantage in thermal efficiency. Chemical efficiency of both models is close enough to be negligible, the differences being only detectible with an exhaust analyzer. I don't have a way of measuring interior temps in the output flue, but the pipe where it meets the masonry chimney is reading about 120* on the exterior, and that's which a good heated mass. Your exit temps are similar to what I've measured on my 6" PBB. Combined with the increased heat output of a 6" PBB, draft will be more than enough to run the system.
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Post by Dan (Upstate NY, USA) on Jan 28, 2014 13:07:59 GMT -8
Would it make more sense to spend the money and effort on more insulation instead?
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Post by mannytheseacow on Jan 29, 2014 6:02:44 GMT -8
Does more output equal more storage when the mass remains the same size?
The price of wearing more long underwear is probably comparable.
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Post by pinhead on Jan 29, 2014 8:07:30 GMT -8
Does more output equal more storage when the mass remains the same size? With the mass staying the same, more energy will be deposited and therefore will stabilize at a higher temperature. This can be good or bad depending on your situation; the room temp will be higher while the stove is running and the mass will charge more quickly. If you continue to burn the stove, the mass temperature will continue to rise and therefore store more energy/heat. This will extend the amount of time the house stays in/above the "comfort zone." As long as the room doesn't get uncomfortably hot while the stove is burning, you probably won't need to increase the mass. The mass in a RMH has one singular purpose: Stabilize temperature. Compare a low-mass box stove to a RMH. The box stove will keep the room at a comfortably warm temp while it's burning but cool off quickly. If you burn the stove really hot the room will get too hot and then cool down as soon as the fire goes out. Conversely with a RMH, it takes some time for the mass to heat and cool which has a moderating effect on the temperature. Even with the same amount of heat/energy released from each stove, the box stove will be hotter and heat the room more quickly (and cool off much more quickly) while the RMH will be initially cooler but stay warm for longer. The more mass in the RMH, the more pronounced the effect. So, ask yourself a few questions: Does the house tend to get too warm while the stove is running and cool off too quickly? If so, you need more mass. Does the stove barely heat the space to a comfortable level while burning but also able to hold that temperature for a while after the fire goes out? If so, you need more BTU's (bigger rocket). Does the stove barely heat the space adequately and cool off too quickly? If so, you need more BTU's and more mass.
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Post by 2tranceform on Jan 29, 2014 8:42:19 GMT -8
Very nice explanation! ^^^^^^ I think this bit of information needs to be in the troubleshooting thread.
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Post by mannytheseacow on Jan 29, 2014 8:46:25 GMT -8
Very good information, indeed, Pinhead. Thank you, that is exactly the input I was looking for.
My stove barely heats the space adequately and cools off too quickly.... more BTUs and mass.
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Post by grizbach on Jan 29, 2014 9:38:25 GMT -8
Manny, If you do go he batch box route, they are more sensitive to restrictions. I don't think you can run the exhaust through a long flue type bench. I converted a 6" rmh to a 6" batch. The rmh exhaust ran a loop through a 4' bench. When I went to the batch I gutted my bench to make it a double bell. Even with the shallow bell system, I had to open up my primary air to get a good burn. When I plumbed the stove right out the chimney, I had a lot smaller primary. I recommend bell systems greatly! There is so much more heating surface area of the bell, it heats up more mass a lot quicker! Terry
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Post by satamax on Jan 29, 2014 10:57:25 GMT -8
Very nice explanation! ^^^^^^ I think this bit of information needs to be in the troubleshooting thread. Yes Ok, just the few last phrases. Or the whole post? Manny, If you do go he batch box route, they are more sensitive to restrictions. I don't think you can run the exhaust through a long flue type bench. I converted a 6" rmh to a 6" batch. The rmh exhaust ran a loop through a 4' bench. When I went to the batch I gutted my bench to make it a double bell. Even with the shallow bell system, I had to open up my primary air to get a good burn. When I plumbed the stove right out the chimney, I had a lot smaller primary. I recommend bell systems greatly! There is so much more heating surface area of the bell, it heats up more mass a lot quicker! Terry Grizz, the batch rocket can push some serious pipe If in a proper mass, with an insulated chimney after, i bet it can do as well as the J tube. Look at my green machine. A real nightmare to start when cold, but after, it works wonders
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Feb 2, 2014 6:23:29 GMT -8
Seems to me, the second paragraph and the last two paragraphs would be best. That is at least how I would do it...
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Post by satamax on Feb 2, 2014 9:23:20 GMT -8
Seems to me, the second paragraph and the last two paragraphs would be best. That is at least how I would do it... Pinhead cut and pasted it.
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