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Post by skywalker on Nov 17, 2020 13:21:50 GMT -8
Hi all, Just finished a batchbox rocket 15cm system with a bell and open dead end bench. The stove seems to be running well but the exit temperature of the chimney feels very low. Through one of the cleaning openings you can touch the internal chimney made of single stainless steel pipes. We also measured a temperature of max 40 degrees ceclius. The chimney gives a temperature of around 80-100 degrees just 10 cm above the stove. To be clear - the chimney starts 8 cm above the floor inside the stove and is going straight up to the ceiling of the stove. Half way there is a bypass made out of a stainless steel t-piece with a valve. Are these normal figures? It feels quite low! Pictures: ibb.co/q7scdfnibb.co/b6ZBH63ibb.co/MfpMCZ4ibb.co/v3qfj6fibb.co/zhGPkMB
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Post by peterberg on Nov 17, 2020 13:43:30 GMT -8
skywalker, I'm assuming the heater isn't dry yet. In case this is affirmative, the chimney temperature will rise somewhat within a couple of weeks. In case your heater is dry already, don't worry about it. Mine is a 150 mm single bell system and exit temperature 1.5 m above the floor beside the heater has never been higher than 120 ºC. Measured in the heart of the pipe, of course. This type of heater, provided it's well built, is able to function very well with a chimney temperature as low as 80 ºC. That's what I get in the shoulder seasons from mine and the testo results are as good as 94% efficiency at lower heating value with a comfortably low CO figure to match. To conclude: as long as the core is producing the specific low rumble and there's no smoke from the chimney it's bang right up to specs. Congrats! Saw your pictures just now and you've installed the T-bar ceiling wrapped in superwool. This detail has been used for the first time for the Mallorca build which is in its fourth season now and no sign of degradation showed up as yet.
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Post by skywalker on Nov 17, 2020 13:54:13 GMT -8
skywalker, I'm assuming the heater isn't dry yet. In case this is affirmative, the chimney temperature will rise somewhat within a couple of weeks. In case your heater is dry already, don't worry about it. Mine is a 150 mm single bell system and exit temperature 1.5 m above the floor has never been higher than 120 ºC. Measured in the heart of the pipe, of course. This type of heater, provided it's well built, is able to function very well with a chimney temperature as low as 80 ºC. That's what I get in the shoulder seasons from mine and the testo results are as good as 94% efficiency at lower heating value with a comfortably low CO figure to match. To conclude: as long as the core is producing the specific low rumble and there's no smoke from the chimney it's bang right on to specs. Congrats! Thanks for your quick response Peter. That clarifies a lot. We are still switching our minds from 'classic' batchbox rockets with channels going through to open bell systems like we learned from your website and this forum. This is so much easier to build and feels much more stable as a system. It's been build some time ago and burned four weeks now. Bottom of the stove still feels a bit humid tough. And how about the chimney being 8 cm off the ground while bench is 32 cm high. Can the chimney go lower? Will this affect the temperature off the bench? (Which is quite good, but could be a bit hotter) And your stove has the chimney outside zo this gives a different exit temperature I assume? Our chimney is relative close to exit heatriser so warms up quit a bit. If this chimney was external i am afraid it will not get hot enough?
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Post by skywalker on Nov 24, 2020 0:11:08 GMT -8
skywalker, I'm assuming the heater isn't dry yet. In case this is affirmative, the chimney temperature will rise somewhat within a couple of weeks. In case your heater is dry already, don't worry about it. Mine is a 150 mm single bell system and exit temperature 1.5 m above the floor has never been higher than 120 ºC. Measured in the heart of the pipe, of course. This type of heater, provided it's well built, is able to function very well with a chimney temperature as low as 80 ºC. That's what I get in the shoulder seasons from mine and the testo results are as good as 94% efficiency at lower heating value with a comfortably low CO figure to match. To conclude: as long as the core is producing the specific low rumble and there's no smoke from the chimney it's bang right on to specs. Congrats! Thanks for your quick response Peter. That clarifies a lot. We are still switching our minds from 'classic' batchbox rockets with channels going through to open bell systems like we learned from your website and this forum. This is so much easier to build and feels much more stable as a system. It's been build some time ago and burned four weeks now. Bottom of the stove still feels a bit humid tough. And how about the chimney being 8 cm off the ground while bench is 32 cm high. Can the chimney go lower? Will this affect the temperature off the bench? (Which is quite good, but could be a bit hotter) And your stove has the chimney outside zo this gives a different exit temperature I assume? Our chimney is relative close to exit heatriser so warms up quit a bit. If this chimney was external i am afraid it will not get hot enough? peterberg, could you enlighten me a bit more on this? Thanks a lot.
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Post by peterberg on Nov 24, 2020 11:21:02 GMT -8
It's been build some time ago and burned four weeks now. Bottom of the stove still feels a bit humid tough. Sounds like it's not really dry yet. Keep in mind that burning wood produces besides heat also CO² and water. Quite a lot, half of every kilogram, pound or whatever need to be get rid of through the chimney. And how about the chimney being 8 cm off the ground while bench is 32 cm high. Can the chimney go lower? Will this affect the temperature off the bench? (Which is quite good, but could be a bit hotter) Temperature in your chimney stack is quite low as it is, I won't recommend to make it lower. And your stove has the chimney outside zo this gives a different exit temperature I assume? Our chimney is relative close to exit heatriser so warms up quit a bit. So you have an internal chimney and still too low temperatures? That 8 cm from the floor means the imaginary ring under the pipe is over 200% of system size, which is sufficient. But in case the pipe is right against the wall you'll lose some (25% or so) of the circumference. Having that pipe in a corner means over half of it isn't useful so it will be down to 100% of system size which is far too small. Remember: the gases need to go through a direction change of 90 degrees at least, quite a volume of it 180 degrees. In order to keep friction low, 90º direction change means 150% of system size is called for. A 180º change need 200% of system size. Mind you, I regard these numbers as minimum values. Here's the question: since there's only 8 cm between the exit and the floor, is the pipe really free all around? If it isn't, raise the pipe upto 15 cm or so. The chimney temps will get higher, thereby a higher velocity of the gases through the system and the fire will get hotter as a result. An external chimney pipe is running lower in temps because it'll loose some heat since it's single walled.
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Post by skywalker on Nov 25, 2020 0:05:52 GMT -8
It's been build some time ago and burned four weeks now. Bottom of the stove still feels a bit humid tough. Sounds like it's not really dry yet. Keep in mind that burning wood produces besides heat also CO² and water. Quite a lot, half of every kilogram, pound or whatever need to be get rid of through the chimney. And how about the chimney being 8 cm off the ground while bench is 32 cm high. Can the chimney go lower? Will this affect the temperature off the bench? (Which is quite good, but could be a bit hotter) Temperature in your chimney stack is quite low as it is, I won't recommend to make it lower. And your stove has the chimney outside zo this gives a different exit temperature I assume? Our chimney is relative close to exit heatriser so warms up quit a bit. So you have an internal chimney and still too low temperatures? That 8 cm from the floor means the imaginary ring under the pipe is over 200% of system size, which is sufficient. But in case the pipe is right against the wall you'll lose some (25% or so) of the circumference. Having that pipe in a corner means over half of it isn't useful so it will be down to 100% of system size which is far too small. Remember: the gases need to go through a direction change of 90 degrees at least, quite a volume of it 180 degrees. In order to keep friction low, 90º direction change means 150% of system size is called for. A 180º change need 200% of system size. Mind you, I regard these numbers as minimum values. Here's the question: since there's only 8 cm between the exit and the floor, is the pipe really free all around? If it isn't, raise the pipe upto 15 cm or so. The chimney temps will get higher, thereby a higher velocity of the gases through the system and the fire will get hotter as a result. An external chimney pipe is running lower in temps because it'll loose some heat since it's single walled. Thanks Peter. Chimney is free all around for at least 10 cm around as the minimum distance. 75% of the chimney is facing towards very lager opening inside the stove.
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