Post by patamos on Nov 8, 2015 0:24:01 GMT -8
Well, that is bound to draw attention.
So i had best make sure the explanation is worth it.
(EDIT: I've cleaned up remainder of the text. Late night stream of consciousness writing and aggressive auto correct can make for quite a mess
The first big RMH i built two autumns ago (picture left) had a chimney fire in the first 3 months (i think?) of operating.
I've been meaning to write about it for ages, but i always seem to have a million things on the go and only find so much screen time (unless i stay up very late…) Finally here we go:
The fire self-resolved after much concern, alarm and smoke. It was a close call, and lots to learn from. The people for whom i built the heater, Suz and Dave had a big metal bodied stove in their old cabin, which tended to have 3 or 4 chimney fires a year… So they were worried by this event, but also seasoned enough to be aware of some of the contributing factors unique to their situation.
Their home, a beautiful light clay building, is in a deep river valley. Way up the Chilliwack river in SW BC Canada. Thick temperate rainforest. Heavy vapour fog most winter mornings. No sun at all for close to 3 months. The river has one of the fastest drops for its volume in North America. Maybe the world. SUper popular kayaking and fly/cast salmon fishing destination. Tons of white water nearby and everything wild...
With all these conditions present, the wood stored outside on the well-covered porch gets wet no matter how dry it was before storing. So starting the RMH with damp wood is pretty much a given. On the upside, this 6.5" J feed system pulls like all get out. Happy to speed up into a big bell ISA without using the start up bypass if prepared carefully. Also happy to switch from bypass flue to bell in about 5 minutes no mater what. It never stalls from a condensation plug. Not even close. So no problem right?
The wildcard factor is that the flue pipe on the second floor is almost all single skin - so as to shed/harvest more heat into that big open space. 800sq.ft. of mostly open floor layout with 6 big windows, 4 of them south facing. We were going to put a small bell there... and might still do so, but wanted to see how this simpler set up would work
The 6" dia. pipe going through the joist cavity is surrounded by a 10" pipe with perlite in between and a couple more inches of space away from the wooden floor and joists. No trouble there. Once that insulated through pipe arrangement is 12" above the upper floor it changes to uninsulated 6" pipe for 10 feet or so, then has a triple wall insulated set up going through the roof.
That uninsulated pipe cools rapidly just above the transition, to the point where you can hold on to it for quite some time within 4 feet above the floor on most shoulder season days. Even after a few hours of feeding. All the while the fire pulls nicely. So one could say harvesting has been optimized.
But because of the easy start up and wet wood, there has evidently been creosote build up within the first foot of uninsulated pipe on the upper floor. Whether that is the definition of a 'condensation plug' i do not know. Anyone please help me gain clarity on the terminology… Whatever it is called, rapid cooling of poorly combusted wood gasses is the issue.
My initial suggestion was to run the heater with the bypass open full blast for a good 20 minutes every few weeks or so.
Also, wait a few minutes longer before closing down the bypass after cold start up. I think this is a good practice any where one is shedding heat from exposed single wall flue down-stream. Like getting ones blood pumping via exercise, these are healthy practices to be in the habit of.
But all the while i have been pondering what remedy would look like. That is not dependent upon user knowhow.
A second bell would very much solve the problem of creosote 'plug' if not build up. But a well-located clean out would make things easy. ANd a return fire in an earthen bell is a lot less scary than one in a thin metal flue.
But, just tonight it occurred to me that adding a 3 foot section of somewhat insulated pipe above the existing double flue into the second floor might be the better idea:
-Attach another length of 10" 26 gauge metal to the one below it.
- Add perlite into the cavity created between pipes. But first sift the perlite through 1/4" screen to separate the fines from the coarse,
- Install the finer 1/4" minus in the lower half of the cavity and 1/4"+ chunks in the upper half.
This will hopefully spread the cooling process out and diminish the chance of creosote building up a plug. It will also move any such plug and in flue reburn into more open space away from combustibles.
Hopefully this will ask less enough of the system under worst case scenarios.
Any and all suggestions and feedback is most welcome
well being
pat
So i had best make sure the explanation is worth it.
(EDIT: I've cleaned up remainder of the text. Late night stream of consciousness writing and aggressive auto correct can make for quite a mess
The first big RMH i built two autumns ago (picture left) had a chimney fire in the first 3 months (i think?) of operating.
I've been meaning to write about it for ages, but i always seem to have a million things on the go and only find so much screen time (unless i stay up very late…) Finally here we go:
The fire self-resolved after much concern, alarm and smoke. It was a close call, and lots to learn from. The people for whom i built the heater, Suz and Dave had a big metal bodied stove in their old cabin, which tended to have 3 or 4 chimney fires a year… So they were worried by this event, but also seasoned enough to be aware of some of the contributing factors unique to their situation.
Their home, a beautiful light clay building, is in a deep river valley. Way up the Chilliwack river in SW BC Canada. Thick temperate rainforest. Heavy vapour fog most winter mornings. No sun at all for close to 3 months. The river has one of the fastest drops for its volume in North America. Maybe the world. SUper popular kayaking and fly/cast salmon fishing destination. Tons of white water nearby and everything wild...
With all these conditions present, the wood stored outside on the well-covered porch gets wet no matter how dry it was before storing. So starting the RMH with damp wood is pretty much a given. On the upside, this 6.5" J feed system pulls like all get out. Happy to speed up into a big bell ISA without using the start up bypass if prepared carefully. Also happy to switch from bypass flue to bell in about 5 minutes no mater what. It never stalls from a condensation plug. Not even close. So no problem right?
The wildcard factor is that the flue pipe on the second floor is almost all single skin - so as to shed/harvest more heat into that big open space. 800sq.ft. of mostly open floor layout with 6 big windows, 4 of them south facing. We were going to put a small bell there... and might still do so, but wanted to see how this simpler set up would work
The 6" dia. pipe going through the joist cavity is surrounded by a 10" pipe with perlite in between and a couple more inches of space away from the wooden floor and joists. No trouble there. Once that insulated through pipe arrangement is 12" above the upper floor it changes to uninsulated 6" pipe for 10 feet or so, then has a triple wall insulated set up going through the roof.
That uninsulated pipe cools rapidly just above the transition, to the point where you can hold on to it for quite some time within 4 feet above the floor on most shoulder season days. Even after a few hours of feeding. All the while the fire pulls nicely. So one could say harvesting has been optimized.
But because of the easy start up and wet wood, there has evidently been creosote build up within the first foot of uninsulated pipe on the upper floor. Whether that is the definition of a 'condensation plug' i do not know. Anyone please help me gain clarity on the terminology… Whatever it is called, rapid cooling of poorly combusted wood gasses is the issue.
My initial suggestion was to run the heater with the bypass open full blast for a good 20 minutes every few weeks or so.
Also, wait a few minutes longer before closing down the bypass after cold start up. I think this is a good practice any where one is shedding heat from exposed single wall flue down-stream. Like getting ones blood pumping via exercise, these are healthy practices to be in the habit of.
But all the while i have been pondering what remedy would look like. That is not dependent upon user knowhow.
A second bell would very much solve the problem of creosote 'plug' if not build up. But a well-located clean out would make things easy. ANd a return fire in an earthen bell is a lot less scary than one in a thin metal flue.
But, just tonight it occurred to me that adding a 3 foot section of somewhat insulated pipe above the existing double flue into the second floor might be the better idea:
-Attach another length of 10" 26 gauge metal to the one below it.
- Add perlite into the cavity created between pipes. But first sift the perlite through 1/4" screen to separate the fines from the coarse,
- Install the finer 1/4" minus in the lower half of the cavity and 1/4"+ chunks in the upper half.
This will hopefully spread the cooling process out and diminish the chance of creosote building up a plug. It will also move any such plug and in flue reburn into more open space away from combustibles.
Hopefully this will ask less enough of the system under worst case scenarios.
Any and all suggestions and feedback is most welcome
well being
pat