rocket stove for water floor heater

Hi, my name is Marcelo and I'm from Uruguay (Spanish country, sorry for my bad english) and I'm very interested in rocket stove. I been watching your forums and other information in the site. Thanks for all what you share.
I'm building a new house and I want to heat it with a wáter floor heater conected to a rocket stove. I'm trying to design one and I want to ask you if youy think this can work or if you have some ideas to tell me to improve it.
Thanks a lot.
Marcelo

Your drawing shows that you are taking heat from the fire with your water jacket too soon in the combustion process. You will cool the fire down and make more emissions because it is less efficient.

Also, I was wondering why your hot water exit is at the bottom of the tank. Look into heat pipes and, at least, understand how they work even if you don't want to use them.

Cindy

Thanks for you quick answer.
So you think it's better to take the combustion chaimber a bit longer (as in the picture 1) or the water tank start more up in the chimney (as in the picture 2).
The hot water exit is at the bottom because I think is better if the water flow in oposit direction to the heat flow, is more efficient to extract the heat, and the flow is forced by a water pump to and from the pipes under the floor.

The heat riser of your rocket stove needs to be a height which is in proportion to the size of the chimney pipe. Once the exhaust has exited the heat riser, then start taking heat out of it.

Howdy Marcelo, welcome to permies !
I think one of the fundemental things about the operation of a rocket is that the heat riser has to be insulated so that it can get super hot. This helps to burn the wood and gasses completely. If you take this heat away from the riser you will no longer have a rocket. So where your water is, should be some sort of insulation.
Then you need to install a drum over that to cause the flow to change to a downward direction then take the exhaust from that chamber and contact the water. So the water becomes your mass, like the cob in a mass heater.

Hi, thanks for your sugestions. If I understood well it is better to do something like this one

Marcelo: I fully agree with Cindy and Miles, you will get some hot water with the heater you designed, but you will burn a lot of wood and the exhaust gas will not be clean.
There are two major requirements for a good wood burning oven:
1. the flame has to be hot, i.e. the combustion chamber needs to be isolated thermally. This leads to clean burning (no smoke) and complete burning (maximum yield of energy).
2. the exhaust gas should be as cold as possible. As colder the exhaust gas is as more energy remains in the oven and is not lost through the exhaust.
The rocket mass heater is a brilliant combination of this two requirements.

Your last drawing (same the ones before) has the same problem that all usual ovens have – the exhaust gas has to be hot to rise up the chimney. But how do you want to heat your water if the heating gas has to remain hot? Yes it works, but a big part of the heat will not enter the water but will leave the oven together with the exhaust gas.

Look at the figure below. Here the combustion chamber is insulated and the flue gas is cooled by the water on its way downwards. To flow downwards the gas does not need to be hot, it can be as cold as you want. Before leaving the oven the exhaust gas is cooled by the incoming cold water. It (the water) takes the last bit of heat from the flue gas. You know, heat goes only from hot to cold, this means before sending the flue gas out you should cool it with the coldest part of your oven-system and this is the cold water. Hot water you take from the upper exit of the copper spiral, here it is heated by the flue gas when it is still hot.

I suppose you are aware of the danger when playing with water heaters. The flue gas coming from the combustion chamber of a RMH is really hot. If the water in the copper tube evaporates and there is no way for the steam to escape, the whole setup explodes. It is not only the mechanical damage such an explosion provokes but also the hot steam that burns you. Make sure the tube is always full with water and the water circulates fast enough to not evaporate. And mount enough security valves. They open when pressure gets to high.

regards
Peter

Peter, thanks a lot for your advise. I think your desing will work better
I know about the risk of using hot water, so I plan to put security valves and a water pump to be sure that the water flow moves fast enough to prevent evaporating.
Do you think that with this I can take most of the heat from the exhaust gas or there is still enough heat lost to put another copper spiral in the horizontal exhaust?
You know if anyone use this design? I think that with the mass of the standar design you can extract more heat from the gas but it's more dificult to distribute in a house of 120 square yards, it's easyer with water pipes under the floor.
Do you have another recomendation to me? is there any plane with measures to do this?
Once again thank you very much for all your time and dedication you have to help others.
Marcelo

Your questions:
No, I have no plans with dimensions, and no, I did not build such a heater yet. It is probably a good idea before you start building to read the book of Ianto Evans and Leslie Jackson and a plan of Erica and Ernie Wisner. This guys have a lot of practical experience and know the pitfalls beginners usually step in.
Yes I think you can extract all heat from the flue gas with just one spiral. It depends on the length (precisely on the size of the interface between the copper and gas) and on the speed of water. By the way, iron tube is much cheaper than copper but more difficult to bend. The lower thermal conductivity of iron does not play a big role in this case.

Easier than constructing a heating system with water is to build the thermal mass through a wall and heat two rooms with one RMH. The barrel and a small part of the thermal mass is in one room and the bigger part of the thermal mass is in the second room. The tubes inside the heat storage of a 8” (20 cm) RMH can be 40' (12m) long. This should be enough for two rooms. I think its even easier to build and use two RMHs to heat the whole house instead of a water heating system.

An other idea is to build a Hypocaust. In principle you do not pipe hot water through the floor of your rooms but hot flue gas. The floor of your room becomes the thermal battery of the RMH. As the RMH acts like a pump it is predestined for this application.

But if you think the best for you is a water heating system the one sketched in the figure below might be a suitable concept. It is a pressure-less system. For DIY it is the better choice compared with systems under pressure. There is only the hydrostatic pressure. The water reservoir is placed on a elevated position compared with the rest of the system. It is a stratified reservoir. Water flows slowly, no (nearly no) mixing of hot and cold water.
[123] is a tree-way cock
A. Normal heating mode. Connection 1-3 open, 2 is closed. Fire in the RMH is burning. Pump is working. The rooms are heated. Hot water enters the reservoir on the upper part and exits it directly. The lower part of the reservoir (cold water) is not affected.
B. Heat storing mode. 1-2 open. 3 closed. Pump is not working. Fire in the RMH is burning. Water circulates driven by gravity (may be a second pump is needed). Hot water enters the reservoir and cold water from the lower part flows to the RMH. The border between hot and cold water goes down.
C. Heating from the reservoir. Using the stored heat. 2-3 is open. 1 is closed. No fire in the RMH. Pump is working and pumps cold water in the reservoir. Hot water from the upper part of the reservoir is flowing to the heated floors. The border between hot and cold water goes up.

regards
Peter

Thanks a lot for your advise. I will try some probes of concept before the permanent one and I'll try to read what you suggest. As son as posible I'll post some pictures and information about my advances.
Again thans for you effort.
Lots of reggards
Marcelo.

Hi, I'm new here.

I plan to heat water in my new house with rocket water heater. After reading lot of web articles I have simple plan for my heater, is it the right way?



On exhaust I plan long channel with exhaust pipe and second pipe with incoming air from ground heat exchanger - it should rise the air temperature by few degrees.

Marcelo Silva : I am more than a little scared for you, I can point out several ways a well designed system can be S.N.A.F.U.d by nature or the hand of man.

Remember the old saying 'There is no such thing as a Convenient Crisis' ! I want you to just consider what will happen to your system with a full load of wood
and a combustion chamber glowing red hot ! Now add ether a total power failure during a cold snap, or a loss of your hot water pump!

1st you need a rapid way to drain down your system, even with a pipe with an inside diameter 3cm or bigger, the smallest steam bubble will rise through your
piping radically reducing flow size, and just before 'The Boom- Squish' it will totally reverse the flow of water as it replaces it with steam !

Within a conventional metal box stove, with or without a water heating insert that will never reach the same high temperatures found in a Rocket Mass Heater,
R.M.H., We can have the same problems .

Once you start your water system draining down, you immediately have to use Fire tongs and remove the burning wood fuel and a significant amount of embers
out of your Combustion Chamber Glowing Red Hot to keep the piping that is no longer protected by water flowing inside it from warping or being totally
distorted/warped/ destroyed !

So now it is still cold outside, but if we attempt to run the R.M.H. to use it as a space heater, we will destroy a very significant part of the water heater ! This
is not an optimal situation!

My only recommendation is to have a complete 12vt pump system and backup batteries good for 48 hrs ! This gives you new different ways for your system to
fail, but I do know people who do this and stash the batteries and charger in the basement. This will work as long as you check it faithfully every other day or
every 3rd day !

With this system you are putting your faith in material things made by the hand of man, it would be a charity to not dwell on the idea of building
this system with just a HOPE that the system will ALWAYS word as planned !

Until the day that there is a commercially available water/fluid pump that works off of the heat energy of the Fluid being pumped, (automatically start up when
the fluid heats up, and Automatically shuts down when there is no more hot water to pump)

I see no way around the problem except extracting the heat for your hot water at a point in your R.M.H. at a point past where you will not get Temperatures
within 80% of the temperature of boiling water ! hope this clarifies things a little, sorry to be such a downer ! For the good of the craft !

Think like fire, flow like gas Don't be the Marshmallow! Comments/questions are solicited and Welcome Pyro - Logically BIG AL!

Marek Wojtaszek : Welcome to Permies, And a Big Welcome to the Rocket and Wood Heater Forums / Threads, With over 19,000 fellow members from all
around the world, you can generally come here 24 / 7 and talk to someone who wants to talk about what you want to talk about, many will have unique points
of view !

No, Fortunately I don't think that this could be made to work, If it could be made to work you would be exposing the water to temperatures in Excess of 1600F /
900-ish C . This could never be made a safe system due to the danger of water flashing to steam !

With a conventional Rocket Mass Heater the hot exhaust gases rise within the Heat Riser, Turbulent hot and isolated from the gas stream in the Barrel, When the
hot exhaust stream slams into the Barrel top, a very turbulent tumble of hot exhaust gases form a perfect Toroid or Doughnut shape of hot exhaust gases*, Here
the turbulence is modified ,with the reduction of turbulence we gain more heat energy and actually reduce the noise as we reduce the turbulence.

This affect has been long noted , but is very hard to describe, to allow for the transfer of this knowledge, and is very hard to collect the measurements to codify
what is happening here, It is however simple to build ,or tell a separate person how to build.

Describing the Transitional area just below that receives the Vertically Falling Hot Exhaust Gases, and channels them horizontally over the top of a large Ash pit
and past a clean out is even harder to describe well and as a result much problems in flow are proven to come from here, much more time is spent here than on
describing the Toroid, I am afraid that this is a very critical shape and your research was led astray by other people who never had the Toroid explained to them !
for the good of the Craft, I hope this helps

Think like fire, flow like a Gas, Don't be the Marshmallow! all comments /questions are solicited and welcome ! Pyro- logically Big AL

* your planned build looks much like a rocket from a side on view, you need to seek out a view of the R.M.H. from the top down, Consider going to our sister site
richsoil.com and click on Rocket stoves, this will take you through a series of R.m.h. Builds one by professionals, or reviewed by professionals ! A.L.

Late note : The original Creator of the R.M.H. spent years to find a location where the use of horizontal chimneys with No vertical chimneys was possible,
then he (Ianto Evans) build his homes in harmony with the terrain, as you probably are seeking to put a R.M.H. into an existing structure, the direction of prevailing
winds can render an R.M.H. with a horizontal chimney unusable for days at a time, In planning your build you should always plan-in a for vertical chimney rising a
Meterabove your highest point on your house !

Hi Allen. I appreciate your recomendations. I am just thinking to use a UPS (like the computers) for the pump and a controller with temperature sensor to operate the pump, to start it if the temperature in the water going out is above 30 °, even with flow control to raise it if increases temperature, and lower the flow if the temperature decrese. I also think to put a lid that goes from horizontal position (open) to vertical (closed), with electromagnetic lock (similar to those used in the doors) to keep it horizontal, and if the power fails gravity drop it upright so that cut air entering the chamber, to turn off the combustion, while the pump also continues to run (with the UPS). With this I thought to eliminate the risk of boil water if power goes off. In the design that Peter suggest if the water boil, it goes to the deposit and the worst that may occur is water going out through the security valve.
Next month I'll try some concept tests and I'll show my progress. Thanks

Marcelo Silva : As a 30+ year Fire Fighter I can report when you slam down a cover on your Feed Tube you are creating a perfect set of conditions, An Oxygen starved,
closed and well insulated container with unburned hydrocarbons well above their Ignition Temperatures. Having done this, you must now let the whole thing slowly cool
down to below the lowest ignition Temperature.

When Oxygen is introduced into your closed container you will have created a 'Flash Over', This was a major plot point in the Movie '' Backdraft'' It won several Awards,
maybe you remember seeing it ! Besides setting your hair on fire it most probably will blow the 55gal drum off of your Rocket Mass Heater with flames, and every cover
on every clean out and even probably damage your vertical chimney !

I am not telling you this to cause you grief, If you refer back to the original scenario I suggested that this event was most likely to happen in cold weather. Not only have
you lost your hot water, you have shut down a major source of heat for your residence and put a time bomb in your house ! For the Good of The Craft !

Think like fire, Flow like a gas, DON"T BE THE MARSHMALLOW !!! As always, your comments and suggestions are Solicited and Welcome ! PYRO - Logically BIG AL !

I understand what you say and then I will focus more on ensuring the pump power for the duration of the load of wood that I put. Also we do not have very cold weather (no snow, winter temperature 0-5 ° C) and power is very stable, very few faults and low duration when they occur. thanks

Hi,

I have built a water heater that works and is completely safe. It can be viewed here: https://sites.google.com/site/mywoodfiredhydronicboiler/

A pump is not needed to circulate the water and natural syphoning keeps the cooler water in the vicinity of the heat exchanger. The water in the storage tank is treated with a tannin based corrosion inhibitor and the tank is open to the atmosphere so no pressure can accumulate.

The water that I circulate through my hydronic system is separated from the storage water by a stainless steel plate heat exchanger.

I agree with previous posters that a closed system that needs an electric pump is potentially highly dangerous. No insurance company would want to insure your home with that type of installation.

Allen Lumley: It is only fast sketch. I plan use large tank (boiler) for the hot water so the water will circulate. I drawed only the core of the stove. I'm new here, but no new in RS

My second tought:


It's front view. I plan something like zaug stoves (zaugstoves.com) but with water coat on it. Water will circulate so there is no possibility to boil it. Now I'm using simple wood stowe made from steel - it has combustion chamber in water coat. Works nice 10 years.

Marek Wojtaszek : O. K. , I seem to be on a self appointed drive to point out the not so obvious faults in Prototypes that people post here, Especially now with so much Stinking
shit being put out there in U-Tube land, people trying to build 'New-advanced systems' who have never seen a working R.M.H., or heard of Ianto Evans ! ( I will have to be very
careful what I post )

Basically, on this side of the Atlantic, we use forced air heat, especially with solid fuels. I have been told by my U.K. friends, that solid fuel-fired closed systems are banned there
and with what they have, if they ever start to overheat the system- the banging of the pipes tells them to draw a bathtub of water !

Our main type of solid fuel wood-fired Boilers, sit outside the house ,usually in a separate building, keeping their wood supply out of the Rain, these also have a water jacket around
the boiler, and need to be carefully monitored to prevent them from becoming Creosote making, yellow smoke (unburned hydrocarbons ) producing monsters that stink up the
Neighborhood ! As hard as this will be for you to believe, our regulating body has decreed that in order to cut down on this problem, that this class of wood-fired Boilers must vent
hot exhaust gas Temperatures of at least 500 F, 310-ish C.

As you have designed your system to be primarily a water heating system, it might be better to insulate Just the top of the Rocket Mass Heaters barrel to let the Toroid formed at
that location generate the last of its heat load, and then Extract the maximum amount of heat from the sides of the barrel. This is to allow the protection of the Heat differential that
runs the R.M.H.s system.

I would also be concerned that the water jacket around the outside of the Rockets Heat Riser would have to be charged with cold water at start up in order to allow for the thermal
differential engine/heat pump to perform normally ! If we had a very tall heat storage tank we could allow the water to stratify by Temperature and with sensors to measure these
temperatures and pump/deliver the heated water to our holding tank at the right end !

There has been much discussion on the use of Pumps and Zone Valves, mostly dealing with the need for backups and a plan for total electrical failure during continuing cold weather
events as it is extremely difficult to damper down a solid fuel fire quickly on short notice ! For the Good of the Craft !

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

About a year back, I posted a note about producing hot water by extracting heat from the thermal mass (below boiling temp) instead of the stove itself (boom-squish style). The idea is to make the system more simple, robust, safe and stable, all because of the much lower and stable temperatures in the thermal mass.
You don't get instant hot water, but then you also don't risk blowing your house up...
Link to my post: https://permies.com/t/22031/rocket-stoves/Quick-Easy-Rocket-Stove-Hot

Hi Marcelo & everyone,
I’m newly here. Don’t speak English so well either.
How did the experience go? I am in Maldonado, Uruguay and I thought of doing exactly the same. And thinking on putting the copper at the bench mass.
Does anyone tried or do something like?
Thanks
Greetings