Starting this thread for discussion about use and modifications of RMH heaters in extreme climates such as that of Canada, Alaska etc...
Elsewhere we were discussing increasing the thermal mass to hold greater amounts of heat. What materials, modern or primitive, make sense? Is containing a large volume of water worth the effort, cost, and flood risk?
Also, system sizing and burn times, does anyone have experience running a RMH in a cold climate and what duty cycle was required? Is a RMH alone capable of keeping a house warm in -35C, or is another heat source required to fill in between firing cycles?
Just trying to pull together some of the discussion and get some of the cold climate ideas collected in one thread.
The house of my grandparents was heated from a single fireplace with air channels to 8 rooms on two floors. The area has cold winters, sometimes below -25°C. The oven was tiled and the very heavy burn chamber was build from cast iron. The solid fuel burner was later replaced by an oil burner for convenience. While the heat capacity of iron is not high it has a lot mass in a small volume. In relation to the costs and other drawbacks the volumetric heat capacity of iron is the second best to water. Water makes the most sense in decoupling heat production, heat storage and heat delivery.
Cast iron is indeed very heavy per unit volume, and it seems to have the 'magical' property of sucking up applied heat at a high rate and storing it. Likely because it is heavy and conductive, allowing it to distribute heat throughout the bulk more effectively than earthen materials. My little cast iron stove manages to remove most of the heat from the exhaust stream with an internal surface area of only about 4 square feet.
Water of course is even better due to the fact that it can transfer heat via convection as well, but is messy and corrosive to metals.
Donkey, those Russian bell heaters are pretty neat and I really need to learn more about them and the 'free gas movement' principles. Going to have to go over Peterberg's bell rocket thread again and try to understand it.
Do you know what the stones right in the flame path are for? It seems they would both quench the flame and retain a bunch of heat that is not easily transferred into the living area. Do you shovel them out and use them to heat up the sauna?
One could use heat pipes to distribute heat faster within materials of lower conductivity. Creating a heat pipes is simple, one needs just to close the tube while the medium is boiling inside. Mesh is not absolutely needed inside if the heat destination is sufficiently above the source. Welded pipes with water as the medium can operate at fairly high temperatures (above 300°C), if the tube walls are not to thin. Paraffin wax provides one of the highest volumetric heat capacities of the not overly expensive materials. The change in volume from solid to liquid and reverse is high and it can burn. en.wikipedia.org/wiki/Paraffin
So I hope we get some more experience shared from RMH peoples in the great white north. I am only at latitude 59 in Homer Alaska which some people call the banana belt of the north but we have decent winters nonetheless. Freezing temps start in september and proper winter usually in october and last until breakup in April/May. It is a long dark winter and heating is an important part of life here. I have been heating with my RMH for three winters now and am blown away by the dramatic shift in wood consumption going down while my comfort level has gone up. I used to heat with 300 gallons of oil and 3 cords of firewood and now I heat with 2 cords of wood and no oil. Things are very different though, I now am in tune with the bench and what I put into it and when and what the weather is doing. I can prepare by banking up the bench (1-2 days of excessive firing) and my place will not freeze for four or five days in below zero F temps as long as it is not windy (my structure is an experiment in natural construction and I have a lot of unfinished areas/air leaks). That fact alone is so important for people living with wood heat. My place holds a more even base temp but I still need to wear sweaters when it is many hours since firing and it is single digits or less outside unless I camp on the bench like my daughter who can't seem to get off of it (unless there is something like skiing or sledding that is more exciting to do). It is so satisfying to ski home after a crazy day in town and snuggle up to the bench and warm up before finally deciding it is time to start a fire. It is a different way of living than push button temp control. I welcome it, but I recognize that some people want to be more disconnected from their heat and won't be satisfied with a RMH. I have a six inch system with only 24 feet of horizontal bench run and I am heating about 700 square feet. Since I built mine, I have built several teaching others in workshops and have come to really appreciate the value of an 8" system with much more mass. The one we built last month has 55 feet of bench run! I do think that RMH's are great for extreme cold if one is willing to have a relationship with ones heat and with the addition of more mass for the more extreme. Water storage is another whole subject that is complicated and best for situations where the heat needs to be moved around. I have some experience with that to share as well in appropriate threads.
but I recognize that some people want to be more disconnected from their heat and won't be satisfied with a RMH.
Without any changes to the RMH design one could turn it easily in to a very convenient oil heater or plainly get rid of some waste oil and take value from it. Simply by placing a pot style burner in the stack and letting an oil feeder dropping oil into the hot pot. The feeder could be driven by gravity or other means.
I am not in an EXTREMELY cold environment, but I want to use water because it has specific heat, which I think is J/kg, that is about 4 times higher than things like rock and iron. I think that is right, anyway.
Where I live, pumps are very easy to get ahold of and they are extremely reliable, so moving a mass of warm matter from place to place is not so hard, given a reasonable amount of time. For me, the biggest problem is humidity because I am well... afraid to use a closed system.
I want to use safe temperatures and safe pressures, and that is possible. If you can do those things, then water is a great medium for heat storage and transfer.
Water is good medium for moving heat around but I disagree with common knowledge, that water is a good heat storage medium. Regardless of it's high specific heat, water has a relatively low phase change temperature which means you can't get a lot of heat into it before it does something (potentially) dangerous. Massive materials, even ones with (compared to water) poor specific heat but EXTREMELY high phase change temperature can be made to store more BTUs per unit mass.. When it comes to transferring heat, the DIFFERENCE in temperature means everything. Heat flows much like a rock rolling down hill, the steeper the slope (difference in temperature) the faster it will roll. So getting a rock (with inferior specific heat compared with water) up to a MUCH higher temperature will do more for you in the long run than a necessarily larger volume of water for the same BTUs of storage and slower and/or less efficient transfer.
It is IMPORTANT to remember, all this stuff is contextual, if you take a particular solution out of it's particular context, you may have a duck when you really needed a goat instead.
And surely this is the point? Assuming that you're not building on stilts, then mass is a much lesser problem than volume (or price) isn't it? Adjusting your figures for densities I found (care of google, :-) ) then I get:
For practical reasons it is very hard to find applicable stuff that could actually beat water as storage media. Paraffin has a safety problem. Water has problems with safety and corrosion and thus requires safety precautions and maintenance. Very high heat has a safety problem too. The clear winner would be iron. While not actually able to beat water under normal conditions not having safety and maintenance problems may be a big plus for some stuff.
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Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
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deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
Oct 21, 2020 6:53:59 GMT -8
BenAlexanderT: Happy new year everybody. I wish you the best
Dec 31, 2020 15:06:14 GMT -8
Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
Jan 16, 2021 21:54:43 GMT -8
gnomedome: i realsie this is from 2009
Apr 14, 2021 8:30:44 GMT -8
gnomedome: i realize this is from 2009 id love to see the photos from this ..as im looking to build a sauna soon similar to this .... if anyody sees this post firstname.lastname@example.org..... the photos in this post did not show up
Apr 14, 2021 8:32:00 GMT -8
dcoyte: I am planning to use a cast iron heat exchanger out of a hydronic boiler set on top of my rocket stove, flue out the top. There will be a pump moving the water through the heat exchanger into an unpressurized 2000 gal tank. Any thoughts?
Dec 31, 2021 6:45:55 GMT -8