Satamax Antone wrote:Eric, thanks a lot for your reply.
About the "fact" that masonry heaters are more efficient than rocket mass heaters, i will have to disagree.
Don't get me wrong, I love what is being done with RMH, but when some of the people on these forums talk about figures & numbers that can't possibly add, that is when I get a little disgruntled.
The bullshit stops when you have real test data.
You can disagree, just look at the hard data and compare a masonry heater to any J tube style heater. Plus a large J-tube firebox is only 8"x8" so you cant get much wood into that space and you are only going to get up to ~7,000Btu's out of any given pound of wood and that is with a heater with around 80% overall efficiency. A typical well insulated home will require around 25Btu's per hr/ sq.ft. so a 1,000s.f. home will require ~25,000 Btu's/hr in Northern MN in January. That is 3.6#/hr or around 86#/24hr heating cycle. A J-tube with an 8x8" firebox will only hold about 12# of wood/fire so you would need to fire the RMH 7X to get the required amount of heat for a very small home.
This is what always seems to mystify the people who say you only burn 10% of the wood. Not Possible. There are only so many Btu's in a pound of wood and you can't magically get more our of it.
As people say; it all depends.
On the type of rocket core.
On the heat harvesting solution.
As far as heat harvesting goes, it all goes to the material that you use and yes dirt and soil is cheap but the density is severely lacking compared to brick and stone. The density is what stores the heat.
On the chimney behind.
It's sure that a cobbled up J tube, with a bench with tubes can seem very inefficient. Tho, some testing done by Peter Van Den Berg, has proven the J tube to be a very capable contender on the efficiency side. Still a fair bit of excess air. But the numbers are real good.
Peter is doing some wonderful work with his batch burner, but he is basically turning the rocket stove into a masonry heater. The excess air is what kills your efficiency numbers.
And if you can beat the CO readings of a J tube, with a masonry heater, you are very skilled.
Unless you are building your fireboxes with 100% underfire air like we did 30+ yrs ago the majority of all masonry heaters built with the Eco-Firebox have CO numbers of ~ .04-.08. This firebox is now the only firebox that can be built in Germany, Austria, France..
The bench and horizontal tubes, i'm not too keen on. I will agree with you, on the fact that there is better heat exchangers and accumulators. But it soo cheap that it makes it worthwile.
The bench is fine if you have a lot of floor space, like 4'x8' with a typical RMH. A standard masonry heater has a footprint of ~2.5' x 4' w x 7' h.
I will add that there's no money to gain here. Most of the rocket builders are here to save money, no to spend any.
I wasn't trying to sell anything here, just dis spell some of the myths that were being thrown around about masonry heaters. I think it is great that with around 90 firebrick and a 55gal. drum that you can make a RMH, add on 3'x6' of heated bed with metal chimney pipe and lots of clay,rock,& sand and you have a decent heating system.
You can also build a simple double bell heater, or even a contralflow heater with around 300 firebrick (~$500) and 200# of refractory mortar ($150) or just clay mortar (which is not technically legal). You can finish the outside of the heater with the same cob/adobe that you build a RMH with or buy ~90-4" solid concrete block ($140 with mortar), or local stone, or reclaimed brick... for free. Use and old fireplace door or buy a new one for $200+. Yes a little bit more educating is involved with laying stone or brick but when you are finished you will have a heater that will work 99.9% of the time and it will have a firebox large enough to shoot out around 360,000Btu's on 1 fire and last 100+ yrs before needing the firebox rebuilt. Plus is sits in a 3'x4' space in your house not a 4'x8'.
Another bonus is that a masonry heater is listed in the IRC so you can legally build them and your insurance company will cover them.
A smaller masonry heater for heating ~1,000s.f. normally only needs 200 firebrick.
When you say, 1000 dols to make a masonry heater. Let me doubt it. It's your job obviously. But If i have read some of the MHA papers correctly, for a long flywheel mass heater. You often hear about 5 or 6 tons of firebricks. Let say, 1700 bricks, that's already a fair chunk of money to shed upfront. I have seen some of your pebble stoves. That would make it cheaper. But there is the concrete problem comming into play in this case. Which is not realy that green a material. And costs a bit too, compared to cheap as dirt cob.
The facts are above and I have built over 300 heaters. I built one monster triple bell heater that was 16' tall but there were only ~1,500 firebricks, I have never seen one to take 1,700 and I have seen a lot of heater building plans. A normal heater will take ~ 300 firebrick.
There might be some monster Russian heaters that are 3'x8'x7'h but almost no one builds those old inefficient styles anymore.
And, then, when you delve into Batch rockets, and bells. I realy doubt any conventional mass heater would compete with the evenness of the burn, and it's efficiency.
Look at the data. J-tubes don't come close,too much excess air. Peters batch box is very good, but to me it is more of a masonry heater hybrid than a RMH. Horizontal firebox, fed into a vertical channel which goes into a Bell or more channels. Yup, sounds kinda like a masonry heater.
You keep thinking that Peters batch firebox with a Bell is not a masonry heater. Why, just because he uses an insulated firetube (that is very expensive) and then Bells/chambers (Just like a Bell Heater). He is getting close to the same numbers that we have been getting for years. Plus it looks an awful lot like a masonry heater.
Normally if it walks like a duck & quacks like a duck..
I agree, for the most part, batch rocket mass heaters are just a smidge different. The core or engine not being a simple firebox, with added air channels.
Peters batch box with added air channels is basically turning into a masonry heater, just Peters version of one. Peter is doing some great work, I like him very much.
I would like to convince you.
Nathaniel Rogers wrote:Hi Mike,
Thanks for all of the input and information. I'll have to spend some time doing research into bell designs and factoring that into my decision. I am similarly more inclined towards a masonry heater for the aesthetics and decreased need for frequent burns. The cost was putting me off, but your info has changed that factor. Down in NC I do have less of an issue with more frequent burns as I wouldn't be running the heater as many days, or for as many hours a day as you would in Michigan. I also have to look into what my local building office will allow me to get a permit for. I look forward to your future posts about your project on Permies.
That Lopez Labs page is awesome. That is some fantastic data on various configurations.