Rocket Heater in Radiant Floor Heat?

I got an idea the other day when I was watching videos of rocket mass heaters; instead of putting the exhaust tube in a bench, just run it under the floor. Would the air keep flowing and give you heated floors? Thanks!

I would consider this as similar to the crawl space question. Anyway, here's my two cents: I am fairly sure that you would run into serious flow problems if you tried to treat flue pipe like PEX tubing, but with proper engineering, and lots of cash, it might be done, and probably won't be natural draft. You could do something like a roman hypocaust, but I don't think you would get it past the building inspector -- at least that would be my hope (Honestly, please, don't exhaust flue gases into or under your house). You could do a hybrid of a hypocaust by insulating a space under the floor, like a crawlspace, and use your flue pipe to heat up the air in the insulated space, rather than cob or stone (use a radiant barrier on the walls and floor, to improve the system). As I mentioned in the crawl space thread, there are designs at bioenergylists.org for tobacco drying sheds that might be adapted for something like that.

As I understand it, anything more than lukewarm for a floor gets decidedly uncomfortable.

it can be done and it has been done twice to heat an entire floor. you will have to decide on the size of floor you want to heat and then Isolate the floor from the pad or outside. A floor done this way does have to be designed that the temp never goes above about 90 degrees F higher than that people get uncomfortable.

Ernie,

Have those two been discussed in this forum? It would be educational to review the genesis of those projects. If they are considered proprietary, I am fine with that.

I would be worried about hot spots, especially if using 6" or 8" flue pipe, but I suppose that an insulated slab of sufficient thickness, warmed slowly over time, could work (perhaps you could put the pipe in shallow sloped trenches to reduce the mass of the mass?). Does 4" and smaller tubing put up too much resistance, or can it be used over small distances of 5' to 10', from one plenum to another?

The tobacco drying barns I referred to earlier were initially designed to distribute heat through 6 flat rectangular cross-sectioned flues, made with brick sides over a layer of insulative sawdust/clay (cob) and covered by 1 cm thick ceramic tile. Getting the flue gases distributed evenly through the six flues was complicated and a simpler serpentine flue with brick and a sheet metal top was used for smaller barns, though the more complex flue design was still recommended for larger barns. The purpose of the new flue designs was to increase the efficiency of the transfer of heat in flue gases to the air inside the barn, while eliminating the safety problems of preexisting designs (additionally, all ventilation air was forced to pass through a horizontal slit positioned over the furnace, to preheat it).

One of the reasons I mention the tobacco barn designs here is to ask if the flat rectangular cross-section of these flues would be of any advantage in transferring heat to a solid mass? They were a significant improvement over the round corrugated pipe use previously for heating the air of the barns.

Just brainstorming. I mean no offense.

no not proprietary and no offense taken. I just want to test for a year before i put the designs out. I dont like to promote a design that is in testing.

I think the flues in tobacco barns are a good model to look at for floor heating but i am not sure how they are done off hand. I would like to see pictures of the system in the barns and drawings of how the channels are supposed to work.

hot spots can be delt with by making your ducting deeper in the floor. the trick is to even out the temp in the whole floor. to do this you adjust the depth in the places that its going too be to hot or to cold. as a general rule you will be starting deep at the stove and shallow when you get to the end of the exhaust.

you will also want to be able to control how hot you are going to want the floor so you will need to make a bypass that will allow you to send the heat up the stack or through the floor.

Thanks,

I have the documents on my computer, but it may take some time to find where I got them. I will post the url's as soon as I have them.

Here are some url's of documents that describe the tobacco drying barns:

http://bioenergylists.org/scott_tobacco08

http://bioenergylists.org/stovesdoc/Scott/malawi/tobaccodry.pdf

http://www.probec.org/fileuploads/fl120336971246586200Phase_2_Tobacco_Barn_CHMR_-_Report.pdf

http://www.probec.org/fileuploads/fl120337035282661100Tobacco_pres_eval_update_Aug_08.pdf


There may be some duplication. Also, it appears that version 4.0 of the Rocket Barn (RB 4.0) has been patented. Good for them. They have put a lot of effort and engineering into it and there are some hefty profits to be made by the global tobacco industry from it, not to mention the byzantine carbon credits market. (When I was looking late last year, I noticed that a tobacco company in India was building hundreds, possibly thousands, of Rocket Barns to bring down costs and increase quality.) It may explain why I have not been able to find detailed plans of their newest venturi furnace and firebox/flue designs.

What you are proposing has been done for centuries in Korea, and it's called ondol (온돌). I've been looking for ways to do this myself, with modern technology, only as a back-up on days my passive solar isn't enough. These days, in Korea, it has been replaced with radiant floor heating... I'm a little afraid of controlling the steam pressure for a wood fired radiant solution, though...even though it would provide more even heat. I want to stay off grid, or it would be a no brainer. Permitting is a concern...I also imagine the under floor flue network could get quite costly.

I've experienced the traditional ondol system, and it typically only heats one really large room. It is not even heat. Traditionally, people congregated differently according to the weather requirements and most living was in one room anyway. Also, they tended to wear more layers of clothing, as in the detailed engineer-written article I attached. There ARE hotspots, but those are actually quite nice - temperature control is similar to moving closer or further away from a fireplace, vs. the oppressiveness of an over-heated room or the discomfort of thermostat wars. (I'm actually not happy with any heating system, as I enjoy slippers and cool floors but also don't enjoy hot forced air in my face) I guess radiators are my favorite for comfort but they take up too much valuable wall footprint...

The genius of ondol and what I'm interested in is that it served double-duty as their cooking stove. Reservoirs for cooking were outside the room so stews, rice, and hot water could stay warm and handy. I hear deaths occasionally but rarely occurred due to CO2 poisoning due to leaks, but also their floors were rather thin and they weren't using modular materials or monolithic materials for the flue construction. Right now, outside my room, I am looking at an ondol-heated cordwood house with shake shingled roof...cordwood structures are also traditional (though rare) structure here. But this farmer does not cook with his ondol and must use portable braziers instead...

I don't know where I'll end up buying land, but there might not be enough winter sun for solar hot water heating of the quantity I'd need to heat my home, so having a bio-fuel backup sure would be nice. Any links to wood/steam systems and/or a pressure release valve I can look into would be appreciated. Just new here so still have to learn about this rocket mass theory...

Suki,

Thank you for the reference. The Ondol and other hypocaust systems have been around for a very long time. When I was looking into them, when I posted earlier, I noticed that the underfloor flue systems had a tendency to have hotspots. I was wondering if the underground flue were treated as a bell, with the entrance to the chimney set very low, would the heat distribute more evenly?

Take a look at this thread at Donkey: http://donkey32.proboards.com/index.cgi?action=display&board=experiment&thread=498&page=1

Also, I was wondering if the draft problems associated with the ondol could be partially solved by putting an insulated heat riser (like an RMH) under the cooking pot? Another solution is to put a draft inducing fan at or near the end of the system. See an example here: http://www.pyromasse.ca/articles/ondol_e.html

Other hypocaust systems I have found are the Gloria, in Spain, and the Taba Khana (or, tabakhana), in Afghanistan and the surrounding region (which is similar to the ondol but uses a tandoor oven at the head of the system).

If you look at the document I attached previously, the firebox is way lower than the underfloor flue system, if that's what you mean by bell shaped. (I'm an unlicensed architect and this discussion is all a theoretical leap, a mildly educated guess) Don't understand how that would help at the chimney end. It's molded in the ground in much the same manner as a masonry fireplace is to control the draft, and the chimney at the other end (I have more documents somewhere) was very short.

I was thinking myself that it wouldn't be worth taking the risk of poisoning myself should a leak occur, and was thinking it would be smarter to use PEX and have it be a separate system. Maybe a reserve tank gets heated by the RMH and there is enough room in the tank for expansion? Or you have the pressure release valve outside...Maybe instead of a direct transfer of heat between the RMH, since it's so hot, it heats a masonry casing surrounding the water tank instead? I'm sure a ceramic tank would cost a fortune...

But like I said, heated floors can be oppressive. Since the floor will already be holding direct gain from my S. window wall, I am thinking heating the North wall would level out the comfort level. In that case, I'd want to see how we could get double duty out of the RMH so it's a fully functional stove + water heater and just incorporate it into my wall. I've seen some pre-manufactured freestanding Chinese models of stoves that also heat detached water tanks. Wish the U.S. certification process was not so onerous.

Maybe wanting to both cook and heat from the RMH on such a grand scale is a pipe dream...(pun intended)

I priced those gassifiers today just for boiling the water. omg. Now I know why y'all are building these yourselves. Am thinking that having a certified mason make the RMH as a masonry stove is the best way to get the thing legal. I worry about permitting a lot. I MUST be in a broadband area for my livlihood, so am thinking that probably equals a restrictive jurisdiction.

Hot spots are nice! If there are cooler areas, then you have personal control. But if everything is hot there is nowhere to go except outside. Seriously. Go stay in someone's home who has radiant floor heating and they like it 2 degrees warmer than you do. You'll be wishing for hot/cold spots. Or, go spend some time at a sauna and stay an hour longer than you feel thermally comfortable. You can add socks or you can go roast your toes until they are warm if you have different thermal zones but you can't take your skin off if everything everywhere is too hot...Also, I think it depends on how many flues are lain. In the document I previously attached, there were many parallel flues, but in other plans I've seen only a couple, so the distribution plays a factor, which is probably why everybody uses PEX right now. Proximity to the heat source as well. In regards to fans, I think one also has to think about access to each gadget one adds to the HVAC as well. If you are on grade, that could get tricky.

Now, one thing I came across that they do in North Korea is they use Ondol for their green houses. THAT's pure genius. My greenhouse (sigh - one day) will be attached, so it will get the same floor treatment as my living space.

Suki,

Sorry, the term 'bell' in this case is not describing a bell shape, but rather a space in which flue gas is introduced near the bottom and exhausted though an outlet positioned lower than the inlet. The heat in the gas rises to the top leaving cooled gas at the bottom which leaves through the exhaust outlet. The heat distribution tends to be fairly uniform with some gradient from top to bottom. Bells were often included in the chimney stack of a house to heat rooms in upper stories. The bench bell described in the Donkey reference proves that, at least in a small bench, the bell works to heat the bench uniformly.

An ondol could be treated as an RMH with the bench installed under the floor. You could run your bench, above or below the floor, along your North wall. If you run the flue below the floor, you could have the combustion unit in an adjacent, lower room, as with the ondol or tabakhana, where you could use the top of the barrel as a cooking surface, or fit a wok or pot or barbecue to it, as has been done successfully by someone, or you could make a rocket fired tandoor oven, which I haven't seen done yet, but ought to be doable. You could also sink the combustion unit in the floor and treat it as a floor furnace with the barrel over the heat riser taking the place of the heat exchanger.

As far as permitting goes, that is probably a crap shoot and will depend on your local inspectors and whether someone has gotten a masonry heater or an RMH passed in or near your jurisdiction. Depending on who has successfully preceded you, adjust your nomenclature accordingly.

Thanks for the bell explanation, I'd only heard people referring to it with no explanation. The floors are about 16-18" above grade. You could drop the chimney side easy enough. I never saw a wood chimney before...

I already got the whole floor = bench thing, though. I must sound really dense or something... However, unless you have a very tiny house, that's not going to get you too far. You'll see by the photos I took that I'm attaching, the volume of combustion to heat a large room was pretty high. Notice there are several doors to refuel.

Traditional housing compounds often had several kitchens. Men were in one area and women were segregated, so there were usually at least two. Sometimes (probably for the rich) there were rooms heated with no stove.

I've stayed at a few of these places and there didn't seem to be a draw problem or smoke problem, except if the wood isn't dry.

A leak due to settling is not beyond the realm of possibility. The problem that could arise would be if at the same time a gap was created in the floor to the living area. A modern super air-tight house could be a real death trap should that happen. If you're going to do this, I'd make sure your house was well ventilated, as traditional houses were. They were quite drafty places, the walls being about 2 inches thick wattle & daub, covered with paper on the inside. The windows only covered with paper. The floors only covered with oiled paper, the paper bends up over the wall paper and there usually aren't baseboards, so separation between floor and wall there is only paper sealing it in in the traditional home, which are all old now.

Suki,

Nice photos. Sorry if you felt talked down to. It was not my intent. Perhaps I have written far too many officious reports and can't get out of the habit?

I understand your concern about leaking CO into the living space. A good stove builder ought to know what needs to be done to minimize that risk.

Heating water is certainly an option, however, it adds a few layers of complexity and expense. If you want a hydronic heating system, you are probably better off with an efficient gas water heater or boiler. There are wood fueled boilers out there, but, as you discovered, they are not inexpensive. You could probably cobble something together using rocket combustion or some other high efficiency combustion system. What you described as far as using an RMH as a boiler might work. You could coil some stainless or heavy gage copper tubing in the barrel. I am sure someone has tried it. Keep in mind the usual warnings about the dangers inherent in heating water.

There are a couple of geysers (hot water heaters) sold in South Africa that might interest you. The CBS Paraffin Geyser, <http://www.cbuying.co.za/paraffin-geyser>; (check the drop down menu to find "How it Works" and "Typical Installations."); and the Shiza Manzi, <http://www.shizamanzi.co.za/>; (the upper video is in Zulu and the lower video is in English.). The CBS geyser could probably take an appropriate sized flame from any source, like a rocket or one of the many TLUD gasifiers. The Shiza Manzi looks like a pocket rocket with a boiler integrated into it, but that may be an oversimplification.

You could store the hot water, as you described, in an insulated, vented water tank, such as are used with solar heating systems. You could probably integrate a biomass fueled boiler into a solar system, along with a conventional natural gas or propane backup. I looked into an evacuated tube system when I was building my addition a few years ago, but the economics didn't add up.

A well insulated house does not need to be airtight, and those that are are required to have air-to-air heat exchangers to allow fresh air in. Still, that is small comfort if you are concerned about CO poisoning.

You can size a stove for just about any space required. I think that the sizes for the RMHs described at this forum would be sufficient for a large room or a small, open floor-plan house. Remember that a lot of heat is dumped into the room through the barrel and that some heat loss through the barrel is key to the system working.

The use of a wooden chimney would indicate that temperatures are reduced significantly by the time they reach the end of the system. I don't know as it would be a good idea to use a wooden chimney in a modern application. If you want to maintain the look, there are cement or cementitious products available that could probably work.

Are you looking to replicate the look of a traditional Korean house, or renovate an existing one? I am pretty sure you could maintain the aesthetics but still keep it energy efficient without necessarily using modern materials, except perhaps for the windows.

Thanks for all the technical info! I was just posting to help out the O.P., but perhaps he is on vacation or given up?

I've got plenty of time to explore what I want to do and just brainstorming at this point. I'm kind of taken with the idea of a RMH stove heating the N. WALL at this point, though...

I think anachronistic mimicry is inherently ingenuous since we all have cell phones, computers, cars, etc., but I do like materials that haven't had their soul stripped from them. So I'd prefer a fusion of something natural with a modern form follows function aesthetic to it. I'm thinking earth sheltered or maybe a wofati, depending on the site. I have always been taken with the dual functionality of the ondol system, though, which is unique in Asia.

https://permies.com/t/16497/stoves/rocket-mass-heater-heat-aquaponic

Check my post here. Same concept but rather than running tubing to the fish tank the water could be pumped through the floor through existing radiant heat tubing / piping.

Andrew Parker wrote:Suki,

Sorry, the term 'bell' in this case is not describing a bell shape, but rather a space in which flue gas is introduced near the bottom and exhausted though an outlet positioned lower than the inlet. The heat in the gas rises to the top leaving cooled gas at the bottom which leaves through the exhaust outlet. The heat distribution tends to be fairly uniform with some gradient from top to bottom. Bells were often included in the chimney stack of a house to heat rooms in upper stories. The bench bell described in the Donkey reference proves that, at least in a small bench, the bell works to heat the bench uniformly.

An ondol could be treated as an RMH with the bench installed under the floor. You could run your bench, above or below the floor, along your North wall. If you run the flue below the floor, you could have the combustion unit in an adjacent, lower room, as with the ondol or tabakhana, where you could use the top of the barrel as a cooking surface, or fit a wok or pot or barbecue to it, as has been done successfully by someone, or you could make a rocket fired tandoor oven, which I haven't seen done yet, but ought to be doable. You could also sink the combustion unit in the floor and treat it as a floor furnace with the barrel over the heat riser taking the place of the heat exchanger.

As far as permitting goes, that is probably a crap shoot and will depend on your local inspectors and whether someone has gotten a masonry heater or an RMH passed in or near your jurisdiction. Depending on who has successfully preceded you, adjust your nomenclature accordingly.

How do you think that could be done? By possibly using the riser as the tandoor? Using a heating chamber/burn tunnel that could be opened and closed would be a way to guarantee the control of temperature. I'm also thinking that you could possibly cast one or make one out of cob, a vertical cob oven.

Rion,

There are several homemade tandoor ovens on the internet. Traditional tandoor ovens had primary air supplied through a tube that entered from the bottom or near the bottom of the oven. There have been several rocket bbq's built: elbows, j-tubes and hybrids. Putting the two together should be fairly straightforward. Integrating it into a RMH would be more complex, but probably doable. a tight fitting insulated lid would probably be key. It should go without saying that such a configuration should put the cooking area outside, or at least in a very leaky room. Just a thought, you might be able to put a wok in the opening, or nestle a cooking pot into the oven, to do double duty. It would need reenforcement around the rim and some pot supports on the bottom.

Good advice, Andrew. I have also seen meat hung from spits inside Tandoors. That would be another option.