sizing RMH for 2400 sq ft room?

Hello All,

I just discovered rocket mass heaters about a week ago and I'm watching everything I can find, and just beginning to work my way through the threads here.

My wife and I own an old church in Eugene, OR . . . single pane windows, no insulation, etc. We're turning the place into a community center of sorts (check it out at http://www.reachcentereugene.com) and the Main Studio is where most of the action is. This used to be the sanctuary room for church services. 24 foot ceiling in gable shaped roof, 2400 sq ft room.

The current forced air, natural gas heater blows through cement ducts under the floor. We're at the low point of the neighborhood and water seeps into the ducts all winter long. Hot air blowing across cold water . . . not good. Suddenly I'm thinking . . . rocket mass heater??!!

What are your thoughts? Will it pass code? How long does the bench need to be? Do I need more than one bench so that I cover the entire space? I don't know where to start. Are there threads here that discuss sizing strategies?

Thanks for any help,

Charlie Magee

Charley Magee : I took the time to look at your Reach Center, It looks very much like a great addition to the Eugene Community, Good luck ! Big All

In an earlier thread we talked a little about what a Rocket stove is and is not and storage of that heat in a thermal bench, and I pointed out that All Rocket Mass Heaters
R.M.H.s need a lot of attention over the 1st 11/2-2 hrs and that the heat you were storing in a Thermal bench would often expend its heat into a room with no bodies
to heat due to your usage- needs.

I just wanted to send you to an alternative build which has the potential to grow into a solution to your dilemma, we often speak as though the R.M.H.+ Thermal Mass
Bench was truly a poor mans Masonry stove/heater, this build comes a little closer to truly being that poor mans Masonry Heater, solving most of the problems common
to R.M.Hs and Thermal Mass. You probably have only just discovered conversations regarding the use of 'Bells' as a way to increase radiating surface area with a major
reduction in mass, most of these types attempt to mix a 'Cob' R.M.H. with metal boxes used as 'bells' for prompt heat radiation - there will be problems with the unequal
expansion rates of the different materials resulting in cracks at the Cob /Bell seal, and problems with exhaust gases, here is a working model that provides a very large
step towards solution of several of the problem areas !!

I wanted to send you to Permies.com/t/27091/rocket-stoves/Rocket-Heater-Masonry-Stove-Built, This is a skilled adaptation of new technology, the dragon heater
unit, and the use of existing tech in the form of Chimney tiles which has a history going back 1,000s of years to the early Greek civilization, hopefully the different
expansion rate issues can be handled with simple high temperature gasket materials, Besides Sandy Mathieu, Ernie Wisner, Kirk Mobert, and Peter Berg have all researched
the use of R.M.H.s and Flue chimney tiles, this technology is still a little too new, and I have not seen one, but this is a 'watch this space ' creation and I will predict great
things at some time not to far off in the future ! Hope this helps, For the Good of the Craft !

As always, your questions / comments are solicited and are welcome. Think like fire, flow like gas, don't be the Marshmallow ! PYRO - Logically BIG AL !

Allen, just my opinion, but i think the chimney flue heater would be a bit small. Or may be with a ten incher.

I think for a 2400ft² room, i'd go for a batch box, or rocket 177 as it's othyerwise known. Imho, it's better suited to less tlc in tending the fire, bigger fuel amounts, bigger heat output.

After, the whole thing is to make the balance between quick heat released by a barrel, two barrels. A bigger metal bell. Like home heating fuel tanks, may be 500gal or even a 1000gal. But this doesn't store heat.

And for storing heat, a cob bench or may be better, a half barrel system. Here the latest experiment

http://donkey32.proboards.com/thread/833/tube-incher-bell-volume

Following Matthew's half barrel, with concrete instead of cob, for added mass. Meant to be surounded by dry pilled bricks, for looks and added mass.

The thing could be repeated for fractioning a bigger mass, and make it transportable (somewhat, this one weights 580 kg aproximately)

Concrete bells could be thought off too. Following Sandy's numùber on the dragon heater page, after a first barrel, temperature is low enough that a concrete bell could hold. Ok, plenty of grey energy, but more rigidity structuraly than cob. And seemingly better heat storing and transmission capacity.

Charlie, what would be the useage of your heater? Somebody would be there to tend it everyday? Or you need to rely on mass for a base temp?

I would say that yes the flue build as shown on the blog might be a bit small, however the same design can be up-scaled to the 8" burner. We will be doing a test of the larger size in the next few weeks. You may want to read this blog about bells versus flues and why bells are more efficient at heat capture.

http://blog.dragonheaters.com/wood-heat-storage-flues-vs-bells/

Concrete bells could be thought off too. Following Sandy's numùber on the dragon heater page, after a first barrel, temperature is low enough that a concrete bell could hold. Ok, plenty of grey energy, but more rigidity structuraly than cob. And seemingly better heat storing and transmission capacity.

I agree.

Sandy Mathieu wrote:I would say that yes the flue build as shown on the blog might be a bit small, however the same design can be up-scaled to the 8" burner. We will be doing a test of the larger size in the next few weeks. You may want to read this blog about bells versus flues and why bells are more efficient at heat capture.

http://blog.dragonheaters.com/wood-heat-storage-flues-vs-bells/

Concrete bells could be thought off too. Following Sandy's numùber on the dragon heater page, after a first barrel, temperature is low enough that a concrete bell could hold. Ok, plenty of grey energy, but more rigidity structuraly than cob. And seemingly better heat storing and transmission capacity.

I agree.

Sandy, you think an eight incher would be enough?

Charlie Magee : A thought popped into my head, you may have a leak in ether your water lines, or the city of Eugene .Additional water from run off will have just that
much less place to go, an make your problem that much worse, The city can dispatch a worker out with an instrument to listen for the leak, ( a small leak can cost the
city 10,000s of gallons and they will want to deal with this-) if they find a leak you will probably get thanked! The worst thing that will happen is that you will have found
a way to get the City to make a record that there is a problem and then you can talk to your City fathers with ammunition in your pocket -pictures help Too*I hope this
helps ! For the Good of the Craft! Be safe keep warm !

As always, comments and questions are solicited and Welcome! Think like fire, Flow like gas, Don't be the Marshmallow ! Big AL

* actually, Make that out side pictures, beyond reporting that you have a wet basement, It may not serve you well to acknowledge you have real problems in a building
the public is known to gather in ! A.L.

Yes, I am thinking it would be, but we will be testing in the next few weeks and give you more concrete answers then, btu output etc. Do you know what you need per hour, and do you need it constantly or during just a few hours when folks are there?

Wow, thanks for all the comments everyone! Looks like I've got some studying to do.

Satamax and Sandy: the usage is to get the room warm by 7:30 for a group of fitness dancers (Nia). Then the room sits empty for several hours and then needs to be re-warmed by 2:30pm for the young girls and boys coming in for dance classes (modern mixed with tumbling.) So it needs to be warm but not so warm that they have to open windows once their body cores warm up from working out. Tricky.

Yes, someone would be there to tend it every day. But much depends on what "tending" would mean in this case. It would be great to get the room up to 65 degrees as a base and have it carry that for many hours.

Allen: it's not the city water getting in, it's the ground water. So, yes, there are cracks in the cement ducting. I'm currently looking into the cost of getting pipe liners put in.

My head is spinning from all the new ideas people are trying out. I'll be checking out these links you've posted.

Thanks again,
Charlie

Do you have AC? Water in the ductwork is bad news and needs to get fixed or isolated. And concrete heating ducts are NOT energy efficient for forced air wet or dry.

If you have AC, you need to fix the ducts. Could be as simple as a spray-in epoxy, could be easier to replace the units with overhead ducting (usually not aesthetic enough for a church sanctuary, but fine for a dance studio).

Code is going to be, ahem, interesting and I look forward to seeing an update. Luckily Ernie and Erica have been doing a lot of heavy lifting in the state already.

Nope, no AC to worry about. And the winter heating bills remind me every month just how bad concrete heating ducts are. This place was built in the '60's when fossil fuel was so cheap you didn't need insulation or south-facing windows or weather-stripping.

Charlie Magee wrote:Nope, no AC to worry about. And the winter heating bills remind me every month just how bad concrete heating ducts are. This place was built in the '60's when fossil fuel was so cheap you didn't need insulation or south-facing windows or weather-stripping.

And only used for 3 hours a week...

Outdoor air handler units are not that expensive--it is probably cheaper to install a whole new system outside the old sanctuary and minimize new duct work. Duct work (especially RE-work) is expensive.

go for it IFF (if and only if):

1) You have a good source for fuel that will match the stove design. The best rocket stove is no good if you only have cordwood.
2) You will ALWAYS have a trustworthy person to manage the stove. No wood stove is idiot-proof, few are even idiot resistant.
Operating one of these things in your home is one thing, in a public space where kids and strangers are playing/dancing/tumbling is a whole new level.
3) You can get code and insurance approval. I see insurance as more critical than city code, see (2) above.

Not sure what you mean by "only used 3 hours per week"

2 hours every morning Mon thru Sat, 5 hours every afternoon/evening Mon thru Fri, Saturday and Sunday afternoons fluctuate.

I was referring to the original purpose as a church. 9-noon every Sunday. and maybe Wednesday night. No point for energy efficiency for such little use, especially since the door is constantly open during that time. Blast the heat for an hour Sunday morning and you are done, insulated or not.

You changed the use of the building, so the original design criteria no longer fit.

Charley Magee : R. scott raised several good points, there are several Energy Saving programs that a public space is Eligible for, usually it is the Utility that gets the Tax Break,
and passes it on as though it was a grant, or uses their 'savings'( Paid for by the customer) to hire a 3rd pary to conduct an Energy Audit, often just following these 1st few steps
will make YOU eligible for additional 'Grants' from fed.state, and local governments !

Combination A.C. / Heat Pumps have a over-unity R.eturn O.n I.nvestment, - Power in Vs power out of 3 X 1 or better, matched up to Grants, this should work in your favor even
if NO-one can explain your water in pipes, Have you contacted your Water Dept. Yet ?!? Hope this helps. For the Craft BIG AL!

R. Scott: Yes, except it was also a school and offices. But the times have changed, the purpose has changed, the hours are longer . . . and fossil fuels are expensive money-wise and earth-damage-wise.

Allen: It's not a public space. It's a privately owned business that rents some spaces by the hour, some spaces by the day, some spaces by the month. It's not a non-profit that can try to get grants. We're on our own, trying to revamp/refurbish a corner in a great neighborhood. It's either that or a developer comes in and tears it down for UO student rentals.

Allen: not sure how contacting the water dept. will help. It's not water from city pipes that's the issue. It's a groundwater issue. Lots of rain in this neck of the woods and we're in a low spot in the neighborhood. Most of the houses on our block have to run sump pumps all winter long. We run two sump pumps and it can't keep the ducts empty.