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RMH Alternatives? Looking for clean wood heating  RSS feed

 
Peter Kalokerinos
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Location: Hunter Valley, NSW, Australia
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Hi All,

This decision is doing my head in so I thought I'd share the dilemma with my fellow Permies.

We're in the process of converting our shed to a home/house. We need a wood heater. I love RMH in theory, but some of the practicalities of using them just dont work for us. That and its a big space. 180sqm (well its probably more like 110sqm once we cut off the workshop end), 4-5m high ceilings - we have ceiling fans mind you.

So what options do we have other than a RMH?
- Masonry wood stove - stupidly expensive
- More efficient wood heaters
- Anything else?

I've boiled that down to two that we can get in Australia:

1. Pyro Classic http://www.pyroclassic.co.nz/
2. Pacific Energy Neo 2.5 http://www.pacificenergy.net/products/wood/contemporary-stoves/neo-25/

If I had to choose, our main priority is clean burn, the less smoke/emissions the better

Anyone know of anything else out there? Are there any proven plans for DIY wood heaters with secondary burn designs? Noting super low emissions requirement.

We have a neighbour who can weld pretty much anything, so a fine looking DIY solution isn't out of the question, so long as its proven.

We have loads of freely available hardwood for burning on our property so looking at pellet stoves etc isn't really an option

 
Glenn Herbert
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Just curious, what practicalities of using a RMH are problematic for you? Do you think you would have to be tending it all day? If heating capacity is an issue, just make a bigger one, and if tending for a couple of hours is too much, make a batch box.

Other than that, I know nothing first hand about particular woodstoves.
 
Peter Ellis
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Everything I've seen says the RMH is substantially the most efficient wood burning heater known.  Don't know what else to say. A rocket mass heater IS a masonry heater, just a DIY version. RMH gives the cleanest burn of any wood burning system I've heard of.

What information have you been getting about RMH that leads you to think there are cleaner, more efficient options?
 
Peter Kalokerinos
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Glenn Herbert wrote:Just curious, what practicalities of using a RMH are problematic for you? Do you think you would have to be tending it all day? If heating capacity is an issue, just make a bigger one, and if tending for a couple of hours is too much, make a batch box.

Other than that, I know nothing first hand about particular woodstoves.


It'd need to be really big from what I gather and yes the tending to it issue. I'm not familiar with batch boxes, I'll investigate. Cheers
 
Kyrt Ryder
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Location: Graham, Washington [Zone 7b, 47.041 Latitude] 41inches average annual rainfall, cool summer drought
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Define 'really big' for your context.

Most homes have use for a couch or a bed and RMH serve excellently in that capacity.
 
Peter Kalokerinos
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Kyrt Ryder wrote:Define 'really big' for your context.

Most homes have use for a couch or a bed and RMH serve excellently in that capacity.


Worst case its about 945 cubic meters, say 34,000 cubic ft. This is due to the ceiling height. You're average "house" is half that in volume
 
Kyrt Ryder
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RMH don't primarily heat airspace, their focus is direct radiation to solid bodies.
 
Peter Kalokerinos
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Kyrt Ryder wrote:RMH don't primarily heat airspace, their focus is direct radiation to solid bodies.


Perhaps I misunderstand their use, but they heat up a big chunk of thermal mass, which slowly releases heat into the surrounding air dont they?


 
Kyrt Ryder
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Nope, or at least- not for the most part.

Air has minimal ability to absorb radiant heat, same reason the sunshine warms you up even when the air is cold.

The mass is a slow-release radiant heater.
 
Peter Kalokerinos
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Kyrt Ryder wrote:The mass is a slow-release radiant heater.


Yep, that heat goes into the air, which is contained in an insulated box, being the home, so to heat up that volume of air, the RMH needs to be a certain size
 
Devin Lavign
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Have you looked into wood cook stoves? When I was researching them I noticed there were a lot of Australian wood cook stove companies that had great products but for me in the US it would be too expensive to import. For you though it might be an option.

On the RMH issue. They tend to be pretty good at not needing to be even lit for them to be heating. While not a similar sized space, Fouch-O-matic off grid found they only needed to run their RMH for 4 hrs a day rather than the 16 hrs for a wood stove when they lived in their yurt. So while you need to tend the fire some with a RMH, one of the big things about them is once you get that mass heated you let the fire die out and the mass keeps heating the space.
 
Peter Kalokerinos
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Devin Lavign wrote:Have you looked into wood cook stoves? When I was researching them I noticed there were a lot of Australian wood cook stove companies that had great products but for me in the US it would be too expensive to import. For you though it might be an option.


We'd dearly love one....but they're north of A$7,000.......trying to keep this exercise to about half that

That and I want to build a double camber cob oven outside....how much wood cooking does one need?
 
Kyrt Ryder
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Peter Kalokerinos wrote:
Kyrt Ryder wrote:The mass is a slow-release radiant heater.


Yep, that heat goes into the air, which is contained in an insulated box, being the home, so to heat up that volume of air, the RMH needs to be a certain size

I get the feeling we're talking past eachother here...

Heating the air is Convective Heat, the kind of heating done in conventional HVAC systems.

wood stove heat is a combination of radiant heat and convective heat, but the radiation is a burning star that only lasts while the fire does.

RMH stores that heat and slowly releases it. Think of this heat as light [because it basically is an invisible spectrum of light.]

When you shine a flashlight, the air absorbs very little of it, most of it shoots straight to the nearest solid body in its path.
 
Peter Kalokerinos
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Kyrt Ryder wrote:
Peter Kalokerinos wrote:
Kyrt Ryder wrote:The mass is a slow-release radiant heater.


I get the feeling we're talking past eachother here...


Perhaps. I understand what you're saying, but at the end of the day we require x btu's or x kw of heat to heat the volume of air (a fluid). Regardless of if that comes from a RMH, a wood fire, or a gas burner. A RMH just does it more efficiently than the others. BUT the mass in the RMH can only hold so many btu's to slowly release, so given our volume of air we need that mass to be larger than normal. Well, its not just the air, its the thermal mass in our slab and any leakages/air exchanges

 
Kyrt Ryder
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If your goal is warm air [instead of warm people/objects] RMH might not be the technology you're looking for.

Perhaps a Rocket-Powered Furnace would work for you.
 
Glenn Herbert
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If a woodstove can effectively heat a place, a RMH can probably heat it better. Woodstoves with their high surface temperatures make a lot of hot air, which will rise to the ceiling and make it hot up there... how does that help the occupants? Fans make moving air currents, which are good at cooling your skin.

A batch box is a start the fire, fill it once and let it burn for an hour type of operation. It puts out heat at about twice the rate of a J-tube of the same system size. Peter van den Berg built an 8" batch box at wheaton labs which heats a 2000 square foot or more drafty auditorium/garage space with a high ceiling, in Montana.
 
Glenn Herbert
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You say you need to heat the air to heat the space, but really, radiant heat warms the objects in the space, which may then heat the air. The air temperature can be lower with radiant heat for the same comfort level. I have experienced this in my house for years, being comfortable with warm floors and 64 F air.
 
Devin Lavign
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Peter Kalokerinos wrote:
Devin Lavign wrote:Have you looked into wood cook stoves? When I was researching them I noticed there were a lot of Australian wood cook stove companies that had great products but for me in the US it would be too expensive to import. For you though it might be an option.


We'd dearly love one....but they're north of A$7,000.......trying to keep this exercise to about half that

That and I want to build a double camber cob oven outside....how much wood cooking does one need?


You might want to investigate Wood Furnaces. I know there are some in the USD$1-2K range that can heat 1000-5000 square feet. But that is from US companies, not sure what sort of availability you have in your country. Just be careful not to get sticker shock at all the $10K and up wood furnaces. There are some lower priced ones out there. Both indoor and outdoor. Here is a link to a US company to get some idea of these http://woodstoves.net/furnaces.htm and they do ship globally if you can't find an Aus wood furnace source.

*edit to add, since pictures and video always make things more fun on a thread. Here is a Fire Chief video explaining their wood furnace line.

 
Peter Kalokerinos
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Glenn Herbert wrote: make a batch box.


Thanks for the nudge in the right direction. Just need to convince my other half now, but I reckon she'll like the idea of lighting the fire once a day, less wood etc. I've also go an idea as to where the bench could go.

Love the ABC Acres one. Might do something similar to that if I get my way

 
David Baillie
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Location: North central Ontario
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So going against orthodoxy for the site here is a link to some stove efficiency numbers the Pacific energy ones are on it.  https://chimneysweeponline.com/wscompe.htm
One pound of dry wood will contain 7000 btu of energy as an absolute maximum regardless of stove.  Wood stoves are rated and should if burning air dried wood at 20 percent moisture  deliver their rated efficiencies.  Heat close to the ground will make your house seem warmer up to a point. My only problem with inside rmh is they are not rated or approved. Where I live( canada) that is an issue because no rating means no insurance no insurance means no mortgage.  We heat our house with a pacific energy Vista in a very cold climate so you need both convection and radiant heat. Our heat load for 1300 Sq ft is about 4 cubic metres of hardwood per year.  That's the average over 12 years.  Included in the stove is approx 80 lbs of refractive brick which help hold heat longer.  My stove will cycle down to about 8000 btu and still maintain an efficient fire.  A full box at night will maintain the house at 20 degrees celcius down to about -20 celci us outside temp.  Lower then that we could wake up at 18; rarely less then that.  All that to say wood stoves have come a long way since their cast iron ancestors.  Nothing against the rocket mass heater but understand the choices and tradeoffs well.
Best regards,   David Baillie
 
Peter Kalokerinos
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David Baillie wrote:Nothing against the rocket mass heater but understand the choices and tradeoffs well.
Best regards,   David Baillie


Thanks David, appreciate your insights. These are the sorts of calculations I've been running through my head as well. Our place is exceptionally well insulated as well (or will be once finished), so that helps reduce the load we well.....we only get down to -1/-2C on the coldest days (so maybe 1-2 days a year). We really only need to increase the inside temp by 15-20C, max

To add to the annoyance of making a decision, we've over-sized our solar system unless we build a house (not happening anytime soon), so as a result we have a LOT of surplus energy we can use....so one option is.....gulp.....air conditioning......philosophically this doesn't sit well with us at all. Last week we had a 50 degree C day and sitting inside, under a ceiling fan it was quite comfortable.....so we dont need cooling and I suspect we'll need precious little heating, but we will need something.....

Lastly, I feel if we use anything other than a RMH, we're not a "real" permaculture farm.....bloody Paul and his podcasts/dvd's....
 
David Baillie
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Peter please do not ever apologise for only needing 20 degrees of gain.  Your summers would leave me panting in my basement.  So in your case I would probably recommend sizing down the unit to one with a smaller firebox.  The reason being burning a stove at its mid range will always give you its best efficiency.  If you have a well insulated house your surfaces will act the same as the mass contained in the rmh.  For us that means a 15 cm slab in the basement with pex tubing in it cement board and ceramics on the main floor and double drywall on all inside walls.  Approx 12 tonnes of mass with no loss of floorspace.  When people blatantly tell you how bad wood stoves are you have to stop them and evaluate their experience
Now here is a question for you:
http://www.epa.nsw.gov.au/woodsmoke/heatercomplies.htm
This link tell me that you have the same regs as us in terms of stoves.  Can you even get a RMH to pass?  Feel free to ignore the question if that is too sticky.
As to "real" well results matter more to me then adherence to orthodoxy.  All technologies have tradeoffs even RMH.  Woodstoves tradeoff would be slightly higher consumption weighed against your labour to tend the stove being much lower and air temp being more uniform. All opinion of course with some real world experience thrown in there.
Best regards,  David Baillie
 
Gail Moore
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http://www.firespeaking.com/

from their home page
Firespeaking is a family business led by Max and Eva Edleson. We are based in Eugene, OR.

We are licensed contractors offering design/build services to Eugene, Springfield and surrounding areas of the
Willamette Valley as well as artists who aspire to share good design principles with the rest of the world.  

We have many years of experience in the construction of masonry heaters, cookstoves, wood-fired ovens,
natural building, natural finishes, carpentry, rustic carpentry, gardening, farming and catering. 

http://www.firespeaking.com/portfolio/the-shop-cabin-stove/

this cabin stove can also have a thermal mass bench built onto it.
they have photos and videos of this on their site.

check out their website for more information...
hope this helps someone who reads this!
 
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