So on we go - The place I want to put the RMH is "not ready" the main floor full bathroom is in the way. It is slated to be removed and replaced with a half bath elsewhere, after a new full bath is put in upstairs. . . ah renovating, love it
So my plan is to build one of those "portable" (temporary) ones in a different, yet close, location. I am looking for a bit of the "best practices" for this. I also plan on re-using the stove part and just building it into the permanent cob bench when the time comes.
I have some scrap 6" ducting from our forced air furnace that is not used. (dirty, old, oil, no chimny) but I think I need to do an 8" system to get the btu for the house. (3000sq.ft. 1.75 story)
Stuff I have decided (but can be told, NO! Do it this way)
1. It will be an 8" system.
2. I already have a 55 gallon drum (it does not have removable lid)
3. Our floors are wood - I got that part covered. (the whole thing will be on a typical stove pad and raised) I will also be following code for wood stove clearances from the barrel.
4. The temporary mass. . . The bicycle/portable one was made out of wood. . . really? but I can't put it on my wood floor. I could use some better explanation with this. That being said, I have a 6' 2"x4" welded fence and will make a "box" full of rocks, bricks, and paver stones out of that. (the temporary mass)
5. I am thinking that the heat riser to barrel gap should be 2" in the top, and all around the sides. (I am looking for about equal heat into the mass and radiated off the barrel - but would lean towards more into the mass. If it is really cold, I can always still light the wood stove)
6. The exhaust will vent directly out the wall (or maybe a window right there)
1. What works better for the heat riser, stacked brick? or a metal tube? (both being insulated)
2. Can I use Roxul insulation around the heat riser? (between the pipe/firebrick and an outer pipe) It's what I already have as we have been putting it in our walls as we go (with the renovations of our 150+ year old home)
3. What about making the J tube out of a 1/4 metal tube (square) and insulating all of that?
4. Most important, What dimensions should I be looking at for my 8" system for the J tube sections, P.38 of the book for A, C, & F. (presuming F is square with bricks, otherwise 8" round pipe right?)
Basically what I am looking to do here is nothing new. I just want to build a system that works. After I use it for a couple of seasons and am ready to move it to it's new permanent location, then I will customize and "make it better" or just move the whole thing outside into some convoluted water heater thing and pump water into the house as it's half setup for in floor heating already. (thats the original plan, but was going to use a $20,000.00 outdoor wood boiler - also as efficient as a RMH but requiring electricity for controls & a blower, as well as propane for the automatic startup feature. It will also automatically "shut down" and put the fire out to save wood. It's really nice and I would still do that except it will costs close to $20,000.00)
It's already getting cold, so I want to gather the rest of my materials and get going.
edit: will this duct work http://halifax.kijiji.ca/c-ViewAd?AdId=526976604
and certainly can produce ~75%-80%~ of the 8'' system ! I would go for the 8'', in the coldest weather that will need back up !
When people ask me where the best place to scrounge used H.E.V.A.C. stove pipe I tell them to look for the house with a large demolition trailer in the front yard and the windows
all boarded up with plywood and particle board, and showing signs of smoke fire damage. Does this sound familiar, Once a Contractor has signed a contract to do demolition and
re-modeling work it is no longer a conflict of interest for a paid or volunteer Fireman to do Salvage work.
We can use any correctly sized duct work, heat runs, or cold air returns, we are not limited to the actual stove pipe, and as the stove pipe will be buried under multiple sealing layers
of tape, clay slip, Cob, Structural Cob, (With straw) and finish Cob, we have no worries if there are some small holes in the 'Smoke pipe" , though it does need to be clean!
Your local contractors, some of whom I expect you will be related to, can often be a major source of help, whether the excavation contractor who knows every source for Clay, and
Builders /Mortar Sand or stones/rubble. or the guy with the dump truck they all know whats going to happen before it does, and when its likely to hit the demolition trailer, usually
your local plumber is the guy who installs new furnaces, and additions, he likely has a pile of ductwork tucked out behind his place some where, usually not under cover, as it is zinc
coated- YOU don't care about a little rust !
Just keep looking for a matching pair of barrels which the Removable full sized end w/clamp! Have you been to - ' villiagevideo.org/products/rmh/scenes ' - this is 3/8ths of
probably the best DVD video of building over a wooden floor, the only thing I would change is going back to Ianto Evans' original plans to glue the heavy gauge aluminum foil onto
the floor with an air gap above, several people have reported good luck with use in hardy board, or hardy-backer board just in place of the pavers, I think I would like both, but have
not found The Hardy Board in my area !
I have had good reports of temporary R.M.H.s in garages, and outbuildings ! By covering their Cob in the spring with several inches of wet hay, straw, or sawdust and then plastic-
reapplying more water as needed, the Cob has been reported to soften and slump in 4 days to a week ! Not the best scenario, for your living room, or it's floor !
Ianto Evans searched for the perfect location to retire to. Finding a hidden valley with a very stable climate and Built his 1)R.M.H.s, and2) then houses ,3) rarely over 15 feet tall,
around his rocket mass heaters, under those conditions the horizontal chimney has worked very well for him ! When you plan your R.M.H. build, plan on a full chimney rising 2
meters over the peak of your house, usually 2 feet above the highest window that can be opened on the second floor is enough !
For an Explanation of why this is needed, watch the village video short film - ' Preparing (your home) for your stove' - though as a fireman who has often had to safely vent
'hot structures' and deal with the internal stack effect, this should just be review, 'Stack Effect' is often the cause of Carbon Monoxide Poisoning in houses that have been Totally
wrapped in vapor barrier !
1) fire brick and insulation hands down !
2) definitely Yes !
3) No! see answer #1
4) as per page 38 fine, I built my last R.M.H. with an ash pit under the Feed Tube, but am not religious about cleaning it out, rather using the accumulation of ash as an additional
area of insulation, with bricks in place of the ash pit I could have more insulation under there
Bon Chance ! I hope this helps and is timely,Think like fire, flow like a gas, Don't be the Marshmallow, Your comments are solicited and Welcome, PYRO-Logically BIG AL !
We have a blog with a chart about insulating materials, which will help you answer your # 2 question. We also have a chart about thermal mass. Pavers of concrete would work better than rocks as long as you are not trying to heat them up too high.
Metal tubing for the heat riser, the burn tunnel, etc. will work great UNTIL it burns up. Steel loses integrity at 1000°F. Stainless steel will last to a higher temp, but its expensive.
I am a partner in Dragon Heaters and we sell an 8" burn tunnel (made from cast refractory) with a vermiculite board heat riser.
A vertical chimney is usually required unless you have just the right conditions at your house.
I am also going to put it in the garage where I already have a really nice 7" selkirk chimney going out the roof.
Now since it is going to be in the garage, I am looking into the "batch box's" or different larger feeding systems.
In order to avoid the "boom squish" I will have a very low pressure release (think I am going to fit a vehicle radiator or at least the fill cap/overflow to the system, they are set at around 15 psi. **) The second form of safety is simply having more mass then I can heat in one "batch" of wood. So I can calculate how cool my tank needs to be before I can safely relight the fire. It will also serve as an indicator as to when I need to relight the fire.
** If I use the whole radiator I could also remove a shit ton of heat in a hurry before things get too hot and do it automatically via a mechanical heat switch for an electric rad fan hooked up to a couple of batteries. batteries state maintained by a trickle charger. I can also heat up the garage/workshop on demand that way too!
video series you will find by going to you tube and in the you tube search field type in ' web4deb channel', You want the rocket mass heater video series, it has some
addaptive ways to use car radiators and a warning about an earlier failure which was overcome ! Bon Chance Big AL
I needed a smaller barrel/tank to hold the water, and got on my local kijiji. Found a free oil fired water heater, and another identical "cheap" one. They have an oil burner in the bottom, and a 6" pipe up the center. The pipe/flue has a baffle in it to slow the exaust for heat absorption. My plan is to mount the two of them above the stove in parallel.
QUESTION: does the draft force come from the heat riser alone? or does it require the barrel as well?
Can I build the heat riser and then just put a T on top to direct the heat into each tank? Do you think a metal T would just melt? Should I build a T out of the fire brick?
I'll try and do up a drawing and post it.
The rocket stove will be of the 8" design (7"x7" square), the heaters have 6" flue in them, the existing selkirk is 7".
I will also box in the whole stove and insulate it with the Roxul. I will also insulate the short run from the top of the heat riser to the tanks.
What I like about using the oil fired tanks is they already have thermal relays, pressure relif valves, and drains on them.
My biggest concern is the draft, and will it be strong enough.
Satamax Antone wrote:This will not work. At the T the gasses will take the path of least resistance.
Did I not mention they are "identical" and I can add a damper to each pipe in order to further balance them if need be. I could even get real fancy and use some sort of automated dampening system so if one side starts to get hotter then the other it would close down slightly. Id rather just balance them. It is done all the time with radiant floor heating, forced air heating etc. I could even shorten a baffle in one or the other to reduce "drag" rather than introduce more. To just say it won't work without any reference is not very helpful at all.
With some more input and confirmation that this will absolutely not work with a parallel setup - I can downsize the stove to a 6" system size and run the 2 of them inline or series as "they" would say. I'd rather not though because then I will have to run it longer, and it may not produce the KW I need to heat the house (and water, and garage. . . )
action failed after 20 -25 years and was never replaced, and the oil burner drain was never used to flush out the calcified mineral deposits in the bottom of the tank! I would
expect little more than 60,000 to 75,000 BTUs out of your 6'' rocket mass heater RMH per hour, slightly less than, to 1/2 of the usual rate in BTUs the oil burner was fired at
One oil burner will be all a RMH will be able to make heat for!
Because you need a Constant Cross Sectional Area, changing from a 8'' system down to a 6'' water heater, then into a 7'' system is problematical, though I am not familiar
with the Selkirk name ! Running an * '' system to feed two hot water tanks will compound the reduction in BTUs available from the 8'' RMH, but may actually increase the
amount of heat that they can absorb due to the slower flowing speed of your exhaust gases caused by dividing the bass flow into two streams, by the time you re-connect
them, increasing to 7'' be fore the 'T'they may well be able to flow through your 7 '' system ! It may well be worth the effort, however while you may be able to heat your
core with this system, i expect that the final resulting temperature of the water will be sub 90 degrees !
Yes you will need the barrel to produce the Heat Energy Engine Effect that produces the draft needed to produce the High Temperature combustion of the wood gases and finally
charcoal efficiently, the good news is you will should be able to use the single water heater ether upright or laying on its side, the bad news is I expect that your old water
heater will not work as efficiently as a transfer agent as you hope ! Immediately after your water heater you will probably need to pass your remaining hot exhaust gases
through a Thermal Mass or a Heat Exchanging Bell !
A quick review is in order here, The original RMHs were designed to be a cheap heater to be D.I.Y Built for very small homes in third world countries, they must ether be used
as space heaters to warm the very heart of a small home, at a central location where they are easily monitored, or they can also be used by persons here in North America
with larger homes who want to turn their Fossil Fuel Fired Furnaces way down low, below 60 dF or colder, and then use their RMH as it was designed as a supplemental space
heater and personal warmer located at the Heart of the home!
Any attempt to use it in any location other than the heart of the home where it is given 'pride of place' will result in one of two results, The 'oh shit', 'I forgot to tend the
Rocket and now it is getting cold in here!' ' I will have to start the fire again' followed by a repeat performance within a couple of hours, Occasionally, for those lucky few, the
RMH will win-over everyone in the house, and the center of the house will shift to that location !
You ether live in close proximity to your 'Rocket' or you find that getting up to 'go tend it' a burdensome chore, eventually the RMH is replaced by another dissatisfied home
-owner who never understood who to use his RMH ! For the Good of the Craft !
Think like fire, flow like a Gas, As always, your comments and questions are solicited and welcome ! Pyrologically Big AL !
late note: Though I expect flow problems with 2 water heaters in line , I will have to think on that one. RMH systems should never have a system where it is physically
possible to close both dampers down to once, or a system with water heaters in line where a single damper can be closed ! that requires more though ! A.L.
Attached is round 2 design (which was actually my first design idea)
#1 is a 55 Gal. drum welded directly to a 30ish Gal. drum which is "the barrel" of the stove.
#2 is the secondary water tank, "the mass" of a RMH.
This setup will heat the water in tank #1 primarily, and then the secondarily, the mass tank #2. The two tanks will be physically positioned and connected to cause a thermal siphon between them. Then a coil in the top of the barrel #1 will take heat into the house. I may even forget about the coil and just pump the water directly. (and plum the "cold' return into barrel #2)
To get around the 6" flue in the oil heater, I could disassemble it, and suspend it inside an insulated box/barrel so the exhaust can flow around and through the center and finally out the 7" chimney. Though I would rather parallel them.
**Selkirk is just what the locals call it, its just insulated chimney.
I think the original furnace (also oil fired) for the house was around 125,00-150,000 BTU. I am looking to build a 100,000 BTU system. Maybe I should look to a "wood gasifier" barrel stove design w/ blower instead. . . sigh. Why does physics have to be so real? hahaha.
All that aside, what do you think of my design with the water jacket right on the barrel of the RMH?
of evaporation, which with your present wood stove is lost to you, when the temp of the high temp exhaust falls below 212 dF, it is because theHigh temp exhaust gases have
given up that latent heat and because we have been given that boon /gift we have to del with the water vapor which unless the (#2) tank is above 212 dF will condense out in
its totality on the skin of the second tank ! You need to think more about how you are going to deal with water handling more than you are about wet insulation at this point,
but wet insulation is also a potential problem ! Cob will 'work in' absorbing the extra moisture out of the system, and will even release moisture from your Thermal Mass into
the rooms, if the humidity gets low !
Like you say, Physics is real, and very interesting ! I will be off line for several days, I will try and look at your original timeline, and see if any bright ideas come to mind !
The ONLY working feeder for a rocket stove I would trust, requires you to look at a you tube site ! from the u-tube search field type in web4deb channel, this should take you
to a very interesting use of a rocket stove, you want to look at the pellet feeder- don't get lost ! A. L.
For the craft ! Big AL !
My timeline is somewhat indefinite, I already have a heating system in place.
At this point I am going to back off and do some more reasearch. What I am really trying to accomplish is an outdoor wood boiler. The key being, no heat is lost to the outside, all of it goes into the water. (other than the bit that has to go up the chimney top maintain draft)
I also want to maintain high efficiency as I already get that from my woodstove. The problem with it is the heat comes on too fast (room gets too hot while the rest of the house is still cold) and lots of heat goes out the chimney. If I could just store that fast heat in water, then move it to the rest of the house to be slowly released I'd be in business, hence my quest to build one myself rather then buy the $20,000.00 model. A RMH might not be the right starting point.
Cheers and thanks for all the info. . . I'll be back. Please let me know if you have any ideas. (I'll be reading, and braving the tube )
A wood stove, even some of the most efficient tulikivi are nowhere near as efficient as a rocket stove.
I haven't read all of what Allen wrote, but he usualy warns people that, a rocket stove elswhere than in the part of the house you're living in is a chore, rather than a pleasant wood fire.
May be a batch box would be more suited. At Donkey's site, one of the participants was calculating the heat output of a batch rocket, and in half an hour, it outputs enough to raise 55gallons of water, only 8 degrees celcius. So, that means if you start at 20C°, and want to near boiling point, you'd be burning wood for about 5 hours, and you'd have put about 200kg in there.
When you say you don't want heat to be lost to the outside world, if your house is realy well insulated, and you have room and muneys, you could look into seasonal heat storage.
Satamax Antone wrote:A wood stove, even some of the most efficient tulikivi are nowhere near as efficient as a rocket stove.
Mine claims 80.5% thats pretty good, and the way I run it, it gets it. I have very little ash and a tone of heat from only 2-3 logs at a time, and I watch the "secondary burn" of the smoke. Yes a Rocket Stove is more efficient as it does not go through the smoldering periods a wood stove does. The other big plus is the exhaust heat retention of a RMH. I was simply saying I currently heat my whole house with a good wood stove - a RMH should be able to burn less wood and do the same job. (if 30% of my heat goes up the chimney, I would expect to burn 30% less wood if I was to "recover" that lost heat) In theory, I could put a barrel on top of my chimney outside, and then absorb the rest of the heat and pump it back into the house, but thats just not going to happen for many reasons.
Satamax Antone wrote:I haven't read all of what Allen wrote, but he usualy warns people that, a rocket stove elswhere than in the part of the house you're living in is a chore, rather than a pleasant wood fire.
And he is right about that - hence my desire for some sort of bigger feed system for less of a chore.
Satamax Antone wrote:May be a batch box would be more suited. At Donkey's site, one of the participants was calculating the heat output of a batch rocket, and in half an hour, it outputs enough to raise 55gallons of water, only 8 degrees celcius. So, that means if you start at 20C°, and want to near boiling point, you'd be burning wood for about 5 hours, and you'd have put about 200kg in there.
I am not familiar with the site, maybe a direct link to said info would be nice and appreciated.
Satamax Antone wrote: When you say you don't want heat to be lost to the outside world, if your house is realy well insulated, and you have room and muneys, you could look into seasonal heat storage.
I am looking at RMH's - money is an issue, I just don't have it. The house is 150+ years old and is not even well insulated by todays standards. The heat loss from the system is undesirable because it is not in my house, so it is simply lost heat. As an example a very inexpensive outdoor woodstove around here known as a wood doctor will be burning (and smoking) outside without a stich of snow on it, meanwhile the ground has 3' on it. Next door will be a central boiler with as much snow on top as the ground because the heat is not being lost to the outside, and melting the snow. It all goes into the water to be put in the house.
allen lumley wrote:. . . the latent heat of evaporation, which with your present wood stove is lost to you, when the temp of the high temp exhaust falls below 212 dF, it is because theHigh temp exhaust gases have
given up that latent heat and because we have been given that boon /gift we have to del with the water vapor
I understand that warm/hot air can and will hold more water/moister and when it cools you get condensation/rain. It is kind of a function of relative humidity, something I am quite familiar with. But you loose me because you are talking about exhaust gasses that are inside the system. I can see condensation forming inside the exhaust due to the "cold" walls at the water - but what about the outside where the insulation is? I get lost there.
As well, you said which with your present wood stove is lost to you Are you talking about our Pacific Energy Summit Classic wood stove? or my current barrel on barrel design?
Thanks and enjoy your time away from the forums, I appreciate your answers to everyones posts.
Peter van den Berg said lately on donkey's site http://donkey32.proboards.com/
There are two kinds of efficiency, combustion and heat transfer efficiency. When the stove is very hot and roaring, the combustion efficiency is high. So the particulates and CO are burned as well. But at the same time the end temp will inevitably rise because of the higher rate of heat production, lowering the heat transfer efficiency.
And to make the picture complete, overall efficiency is the combustion efficiency multiplied by the transfer efficiency. For example, when the comb. eff. is 90% and transfer eff. is 80%, overall eff. is 72%. The other way around, when combustion is 85% and transfer 95% you'll get 80.75% as overall. That last one is ridicously high by the way, I have seen that figure only a couple of times during the years testing all my experimental stoves.
And oh yes, the excess air is another factor which do influence the numbers a great deal.
The seasonal heat storage was just an idea which poped under my skull, when you spoke about water and insulation. Ok, seasonal heat storage is expensive, needing at least 2750 gallons of mixed water and rocks And of course, all of this insulated!
Imho, you'd be better to get back to the first plan of having it inside the house. Cos, to get a water heater rocket right, it will take you some time. At some point you said the house is 150 years old. Do you have brick walls inside? This would be a big step ahead in terms of lighter mass heat storage.
and 10 hrs of sleep, woke up dry, but before I was done ended up trucking a lot of wet tentage back north!
With High winds promised for today, it is more important to mow the lawn and not have to deal with grass clippings than to borrow a bay at the Edwards V. F. D. to dry tentage
maybe latter today !
I am sure some one will jump in with the right figures but 15% - 20% of 'dry' fire wood is water. All the energy that we get from 'Burning firewood' is locked up in Hydrocarbons
in an ideal perfect world, we could turn this renewable resource into just, H2O, and water vapor.>>>>we come pretty close ! The water vapor produced by burning the wood
has been estimated (depending on Species), to add 20% - 30% !
Here I need to skip to what happens when we heat water to bring it up to boiling from 55dF, 63dC, all of the heat energy that we use to bring the waters temp up to ~211dF,
~99dC ,is almost equal to the amount of additional heat energy transferred into the water to raise it that lass degree up to boiling, it makes zero difference which scale you use.
So we have a great deal of heat energy locked up within the hot exhaust gases ! Several hundred Thousand BTU's. This is called the 'Lost heat of Evaporation', and would be lost
if we allow the water vapor to leave the chimney at any temp higher than the Boiling point of water !
Because we design our RMH's Thermal Mass to absorb the heat energy (and all of the moisture !) of the hot Exhaust Gas to temperatures well below boiling, we gain the latent
heat of evaporation back again! This never happens with any regular wood stove that is run exactly the way that manufacturer recommends because the exhaust gas temps
are to high!
It is the appearance of small amounts of water drops, that signals that this temperature has been reached, and not the condensation itself that releases the energy !
With Frozen Water, we have that same magic spot moving water from a solid to a liquid !
Now I can answer your original question, As your hot exhaust gases make contact with the outer surface /skin of your now naked water tank, water vapor will condense against
that surface,( as it gives up its latent heat of Evaporation) You will need to deal with the physical effects of that water vapor,( with planed for drainage )otherwise you can end
up with Moisture escaping your heat exchanger and wetting your insulation OR collecting inside the air/water tight vessel that holds your re-purposed water heater. The same
amount of moisture that creates problems here could be easily absorbed by a Cob Thermal Bench for re-radiation to the person and to the space !
This problem also happens within all boiler systems at the interface between the Boilers water jacket and the hot exhaust gases, here the big problem is to not lose so much
heat energy that you can't burn your wood efficiently/cleanly ! ( and the reason that an out door boiler costs $20,000 CAN !)
Sorry this was late, BIG AL !
I think I have a new plan that goes basically back to the design by the food forest guy on you tube. I will do up a diagram later for some approval/thoughts.
GREEN - water pipes
BLUE - water in water tanks
RED - hot stuff, flame or exaust
DIRTY GREEN/BROWN, maybe TAN - Insulated (Roxal) outer surface, to keep all the heat in.
not diagramed is the normal insulated places within the rocket stove. I will be insulating both the heat riser and burn tunnel as well.
Thoughts? Again, it is not to scale. The water tanks are actually close to the same height of a 50 Gal barrel.