Calvin Cox

Thanks Paul. I am all for a non motorized safe system if I can get one that will work for what I need. I had the understanding that you can't gravity feed a hot water tank that is lower elevation that your boiler, is this the case? And also the 4 sqft space will not house enough hot water to heat a 2000 sqft house in -40c with a 40 mph wind. As well as domestic hot water for a family of 6. As I mentioned I would like to store enough hot water for 20 hours of use. I only want to run the rocket stove for a few hours each evening while we're home to babysit it. Ideally the electric elements in the hot water tanks would never have to cut in.

Awesome design!

Thanks for increasing the solutions guys. That is a lot more beneficial than predicting death and Darwin awards. I'm going to experiment with these designs irregardless so it's nice to have some suggestions before I hit the shop.

Paul I tried to research that site and all I found was a company selling wood stoves. Not a lot of water heating info. Do you perhaps have the link?

I am on the same page with parallel pumps, sort of, I like a primary and a secondary in parallel both capable of moving more than enough water to keep the system at a safe temp independently. I work in an industry that plans for failure so we always have a plan B and C for every system. I think it will be wise to have all pumps and valves ran off 12v batteries so will have some time with power outages to keep the system under control. Batteries would be fully charged off grid power. The large diameter gravity system won't work for me since I'm not willing to give up 100 sqft of main floor living space to house my mechanical room. It needs to be down stairs.

Paul do you have any more info that you can share about the design and operation of your system? Always best to learn from someone with practical knowledge.

Al: what you were mentioning about taking heat too early, is that only a problem till the stove hits its ideal operating temp? If you let it get upto temp then start taking heat just outside tbhe riser will stay still have negative effects?

As for dousing the fire, if an over temp was probable a pot of water down the feed would likly do the trick. Other options would be snuffing it or pull the sticks out and toss them in the metal ash pail and out into the snow with them. Not too worried about controlling that aspect. Rockets need a baby sitter as it is so this one would be no different. I'll have temp gauges all over this system linked to one monitoring panel. As well as one analog temp gauge reading fluid temp on design #1.

As always, keep the tips coming!

Al, read line 5 in my original post, and thank you for your one suggestion of using larger diameter pipe coils.

Bill, thank you for your great reply! I also had the same understanding as you about containing all the heat possible until the air leaves the heat riser then it's free game to steal energy from. If this wasn't the case wouldn't the barrel be insulated as well?

As you mentioned 1 lb of wood would heat that water in a hurry, theoretically. I have built one of these already but I couldn't get it to draft properly. I think I had wet white poplar. I just brushed the snow off and cut it out of the bush, it was dead fall or dead standing. I have 1 year seasoned white birch for my next test. I built one similar to design #1 except the top of the reservoir was open, no lid, and I just filled it with snow then fired it up to see how long it would take to boil then I would have a bit more info. That was on a 6" round duct feed, burn tunnel and riser all housed in a 55 us gal drum. I think that is marginally enough room to have an adequately tall enough heat riser. So after much tinkering the thing didn't work properly so I never did get to boil the water. The prototype I made a week before did get the top center of the barrel to over 900F, pegged my thermometer.

I was thinking if you can get 900F at the top center of the barrel and alot of people say they have 300F leaving the barrel that would be safe to say you are utilizing 60% of the available heat before it leaves the barrel. Does anyone have any info on how many lbs/hr 49 sq in system would use? Until then I will assume 16 lbs/hr.

16lbs is potentially 96,000 BTU, if the stove is 90% efficient in converting the wood to heat you have 86,400 BTU to play with. Based on last assumption of using 60% of the heat in the barrel you have 51,840 BTU to use in the barrel. If you could capture all 51,840 BTU into the water, which you won't because you'll still be losing some through the barrel walls, you could heat 518 lbs of water by 100F or 51.84 imp gallons, much easier conversion than us gal.

You now need to move 51.84 imp gal, 235L or 61 us gal every hour. That is .86 imp gal per minute. Pretty slow pump. Even if you could capture all 96,000 BTU into the water you would need to move 1.6 imp gal per minute. If you doubled the wood consumption to 32 lbs/hr and kept the 100% efficiency and 100% capture rate you still only need to move 3.2 imp gal per minute.

If I only wanted to run this thing for 4-6 hours a night and I'd like my 50 imp gal tanks at 185F when the stove shuts off for the night, I need to heat tank 1 by 45F = 22,500 BTU, tank 2 by 63F = 31,500 BTU, tank 3 by 81f = 40,500 BTU and tank 4 by 100F =50,00 BTU I need a total of 144,500 BTU. 144,500 BTU spread out over 4 hours is 36,135 BTU/hr. Judging by these rough calculations that don't account for thermal losses to the air the 16 lbs/hr would be too much. 11 lbs/hr would be better. Or I could add more water tanks or have larger water tanks to absorb more BTUs. But as we all know things in practice don't always work as they were planned in theory.

I would love to hear from someone who has tried the coil or the reservoir so I can get an idea of many many BTUs will end up transferring into the water.

Am I missing something here because I don't see what makes these things Big Al's "flaming units of death".

Bill that is great that you have a boiler background that is a great resource in getting one of these rocket heaters successfully converted into a useful water heater. Keep the GOOD suggestions coming.

Hi guys! I have spent countless hours on this site and learned alot of information. I love the efficiency of the rocket stove, particularly the RMH. Unfortunately I'm not too keen on having a bunch of cob in my house but I do like having a wood burning stove in it. My plan is to build a rocket stove that will heat water and cycle it to water storage tanks in the basement. There will likely be four tanks, the hottest two will have electric elements in them as back up. The wood heat will be supplemented by solar thermal evacuated tubes. The farm that this will be built on is North of Saskatoon, Sk, Canada and there isn't natural gas piped in there. Other heating options are heating oil or LP both I think are too expensive and will continue to rise. I have chosen electric, solar, wood since electricity is already ran to all yard sites and it is simple and you only have one bill. The solar and wood will offset the electric bill. There is no shortage of white & black poplar, spruce and white birch near by.

My goal is to extract 50-75% of the heat from the rocket stove through the water and have the remainder convect, radiate into the living room. I am looking for practical experience from anyone who has built or seen a design similar to one of these work. Which would extract the most heat from the rocket stove to the water without lowering the efficiency of the stove?

The first stove has a water reservoir directly on the rocket stove that holds ~45 liters, 24" round x 6" high. In this design the small amount of water would also act as a small thermal mass once the stove has been shut down. I think the temp in the tank will also rise slower so in the event of the system temp rising too high the stove could be shut down before the temp in the reservoir got too high. Surface area is about 452 sq inches and the temp is hottest on that part of the barrel.

The second stove has ~1/2" ID copper pipe coiled inside the barrel and spiraled like a pinwheel at the top. This design could have 28 loops with a circumference of 18" totaling 2400 sq in of surface area, if my math is correct. 18" diameter is 56" circumference x 28 loops + 1500 linear inches x circumference of pipe 1.6 = 2400 sq inches. Plus the area of the pinwheel spiral under the top of the barrel, I don't feel like calculating that haha. This design has more surface area but at a lower temperature along the sides of the barrel but I still think it will capture more heat than design 1.

The third stove combines both the stoves together, it takes the 28 loops along the side and then dumps into the 45 L reservoir on top of the barrel. I built this one because I like having a bit of thermal mass on the stove and I wasn't sure how the pinwheel spiral of pipe would affect the airflow through the stove.

I haven't drawn any of the T/P relief valves yet and this will be a closed system and it will be running on some type of antifreeze since it will need to cycle up to the solar collectors. Barrels 3 & 4 will also have this fluid. Barrels 1 & 2 will contain fresh water. I will be building the stove but the system will ultimately be designed and installed by a licenced plumber.

Line 5: Hot water can make steam, yes I am aware of it and if proper precautions are taken water will not reach that temperature.

Thanks in advance for your input! Calvin

I tried to attached two images, we'll see if they worked...