Bypass valve on a Rocket Mass Heater - send heat to greenhouse?

I'm totally new to Rocket Mass Heaters (maybe this has been done before?) and this struck me as very interesting - about 1 minute into this video there's a bypass valve idea.



I'm not totally sure what's going on when using the bypass (where is the heat going? - it's designed to not heat the floor and just the chimney for a short period - what is the key advantage there?). Anyway I was thinking, apart from being aware I have a large knowledge gap on these things, how about in a new build house you built an underfloor heat system like in the video but attached a greenhouse to the side of the house and added a bypass valve switch to heat the greenhouse as and when you wanted. During winter you could switch the heat across to the greenhouse once the house is nice and warm to keep things toasty and keep the plants happy.

Sometimes you don't want to heat the whole house, just enjoy a bit of fire or heat up a cup of tea. That bypass would almost turn your Rocket Mass Heater into a Rocket Stove with a simple built in adjustment.

Also, even during the winter time, as Erica mentions in the video activating that bypass "reduces drag" which you can translate to "improves draft". Especially during starting the RMH having a better draft will keep things cleaner, get the rocket to operating temperatures faster and basically improve a lot of the experience.

Mike Leo wrote:Sometimes you don't want to heat the whole house, just enjoy a bit of fire or heat up a cup of tea. That bypass would almost turn your Rocket Mass Heater into a Rocket Stove with a simple built in adjustment.

Also, even during the winter time, as Erica mentions in the video activating that bypass "reduces drag" which you can translate to "improves draft". Especially during starting the RMH having a better draft will keep things cleaner, get the rocket to operating temperatures faster and basically improve a lot of the experience.

thanks Mike, that clarifies it nicely for me what the switch is for. I guess in this case the top of the barrel in this case would be great for cooking on at this stage?

What about adapting the bypass to go heat the attached greenhouse idea?

You could definitely do that as long as the run doesn't reduce your draft to the point where it causes problems with the burn.

Another option would be to have the majority of the thermal mass serving the house, with a pipe coil in the thermal mass to move water from the RMH into the greenhouse or anywhere else you wanted extra heat. You'd probably be running the RMH more often because you are using more heat. You would also have to decide if you wanted a passive thermosiphon transfer or a more active pump driven transfer of heat but it would give you a lot more control and distance (especially using a powered circulating pump).

Mike Leo wrote:You could definitely do that as long as the run doesn't reduce your draft to the point where it causes problems with the burn.

Another option would be to have the majority of the thermal mass serving the house, with a pipe coil in the thermal mass to move water from the RMH into the greenhouse or anywhere else you wanted extra heat. You'd probably be running the RMH more often because you are using more heat. You would also have to decide if you wanted a passive thermosiphon transfer or a more active pump driven transfer of heat but it would give you a lot more control and distance (especially using a powered circulating pump).

So is that rocket mass water heater (or a hybrid) underfloor heating with a divert option? Sorry not clear on that as its early days for me getting my head around it.

I was thinking over the warmer months you wouldn't need to use the system that feeds warms the house or greenhouse but maybe use the divert to the greenhouse late evening to heat that overnight from the autumn onwards and of course switch between the house and greenhouse as necessary ongoing as it gets into the colder months.

You can move the heat in a few ways.

1) Air - this is what you usually see in a RMH, the flue gases are allowed to travel a circuitous route and heat is delivered that way. In the diverted example from the video it's a question of which path gets the heat.

2) Thermal Mass Radiation - stone, masonry, etc. which having soaked up heat is able to release it through infrared radiation. This is the way your RMH heats the room it is in (because if the gases were doing it directly you'd have a death problem).

3) Water Mass - Denser than air, able to serve as a type of thermal mass, water is also more portable than chunks of hot rocks. So for situations where you want to move heat but cannot (or don't want to) run large amounts of flue pipe to transport gases water is the medium of choice. This is also why conventional forced hot water systems and radiant floor heat installations usually use water.

Having set up a heat exchange coil, which can pull heat from your masonry in the RMH into water you can then move it anywhere. It could heat the water for your home, it could run through your conventionally plumbed baseboard heat or radiant floor heat, and it could run out to your green house, garage, etc. You could even use more conventional technology to set up thermostats which control circulating pumps so that the "heat" kicks on in the green house only when you want it to, and when it does it draws heat from the RMH to do so.

Of course this could work in reverse for you as well, allowing for collection of heat in the greenhouse to be brought into the home.... but that's not really what you asked.

In some scenarios running the actual flue pipe and using the air to transport gases is easiest. Often that means where you need the heat needs to be fairly close to the RMH, the flue pipe needs to be able to get there with a minimum of twists, obstructions, and drag and there is a maximum limit to how far you can transport these hot flue gases based on your draft. This doesn't take into account the cost difference between flue pipe and copper pipe, and the insulation said pipe needs to get your heat to the end of "the line".

thanks Mike - It begs the question if anyone has done something like this?

Someone absolutely has, though it's not always going to be something you can find on youtube with proof.

What tends to happen is someone who wants an RMH may experiment with one in the greenhouse then decide to build one inside or, having been sold on the technology with the one they've used in their home build one outside just to service the greenhouse.

Pretty much anything that needs heat can be served by a rocket stove or rocket mass heater, it's just a question of application and design at that point. If you're building your RMHs from recycled materials at low expense building several might be better than a larger more elaborate construction that would serve multiple areas.

Jason Matthews : Welcome to Permies, The video that you watched Is about 4 yrs old, and was put on You Tube to show a few good designs and draw interested people
to Permies.com and richsoil.com! You have now seen and heard Erica Wisner, who with her husband Ernie Wisner, are the moderators of the Rocket and Wood-burning
Stoves Forum Threads, and heard Paul Wheaton your host here at Permies.com . A look in at richsoil.com will let you click on Rocket Stoves,and connect you to a whole
series of Videos superior to You Tube and vetted for general Safety .

This was an experimental build, and was built at a remote location separate from Ernie and Erica Wisners home, so there has been no follow-ups to 'prove' the long term
effectiveness of this device,while I have been told that his Unit is a functioning unit, and have seen a sketch of the plans, IT is not one of the approved designs products
that can be found for purchase at ernieanderica.info .

Here is where I suggest that you consider going to rocket stoves.com to get a PDF Copy of Evans' and Jacksons' great book- 'Rocket Mass Heaters' , there is STILL
no other Book in any language with more Rocket Stove, Pocket Rocket, and Rocket Mass Heater family information !!! (and I don't make a dime )

Learning How to safely use a Rocket Mass Heater To Safely function as a hot water heater should be contemplated as a 5-year Project, this is because of the many ways
that it is possible to make a mistake and Cause an expanding steam explosion, referred to here at Permies as ' Boom - Squish ' Think boston massacre with more 2nd
and 3rd degree Burns ! If you have not already seen the 'Mythbusters ' Video exploding water heater you can search for it on You Tube !

In no way should this discourage you from following your interest in Rocket Mass Heaters R.M.H.s, It is just that you should be aware at each step the personal requirements
to proceed to build a safe project ! I hope this helps and is timely. For the Good of the Craft. Think like fire, flow like gas, Don't be the Marshmallow .

As always, your comments and questions are solicited and welcome ! PYRO - Logically BIG AL !

allen lumley wrote:
Learning How to safely use a Rocket Mass Heater To Safely function as a hot water heater should be contemplated as a 5-year Project, this is because of the many ways
that it is possible to make a mistake and Cause an expanding steam explosion, referred to here at Permies as ' Boom - Squish ' Think boston massacre with more 2nd
and 3rd degree Burns ! If you have not already seen the 'Mythbusters ' Video exploding water heater you can search for it on You Tube !

5 year project? I take it the Boom Squish DVD doesn't address the safety issues with heated water? Is it really too tricky to devise a failsafe mechanism?

Jason Matthews : A simple test to see if you were ready to attempt a project like Hot water from a Rocket Mass Heater, would be your ability to draw a complete Domestic
Hot water system, with supplementary solar Hot water, and/or a Solar Domestic hot water heater with Electrical or Fossil fuel fired Backup for domestic hot water heating !

The next step would be to be able to draw a hydronic water heating system with solar as primary and as back up! And while we are on that subject did you see the News
reports of the Jaguar that got melted from sun rays reflected off of the curved wall of a London building under construction ! TRUE STORY !

Note that with all the previous systems there is always a way to drain the system down and/or turn off the back up heating units! Attempting to drain down the water from a
working, extremely hot Rocket Mass Heater R.M.H., could cause the very outcome you are trying to prevent! Also with the previous systems a loss of power to operate pumps
and valves is problematical, but is generally covered by these units built in controls.

With the R.M.H. loss of power to pumps and valves, most be coupled with the owner operator being in attendance to quickly reduce the fire and the amount of heat being
produced! As currently being built, an old fashioned wood stove damper can not be used,-ever! and Attempting to cover the mouth of the feed tube of a hot working R.M.H.
will create the exact conditions recorded in the movie Backdraft !!! Removing the cover after 1st covering the feed tube should require waiting until the entire R.M.H.
is cold ! This would be contrary to what you would usually want to do during an Electrical Power Outage -

Please remember that in all these scenarios, You most be the one to make the right decision for you and your family ! Hope this helps ! For the Good of the Craft!

Think like fire, Flow like gas, Don't be the Marshmallow ! As always, your questions and Comments Are solicited and Welcome ! PYRO - Logically BIG AL !

@ Allen

This seems to imply the design can be made safe enough:

https://permies.com/t/3352/rocket-stoves/Rocket-Stove-Water-Heater#28029

and this is similar:

http://permaculturenews.org/2013/05/20/how-to-build-a-rocket-stove-mass-water-heater/
http://www.youtube.com/watch?v=YTnr8ua54Uw

I guess they are outdoor for the reasons you mention, but it looks a very workable system. Could you comment on the safety of these?

Jason Matthews : I am not trying to say that a true Rocket Mass Heater can not be made with out enough safeties to allow day to day operation of a R.M.H., I am just trying to
make sure that everyone who contemplates using any similar system be aware of the strong possibility that 'Someday, when you least expect it', something will 'go wrong ' and
the likely hood that you will have simultaneously, an Extremely hot R.M.H. well loaded with wood and a plumbing system that can not be shut down in any manner that will allow
the system to become pressurized. It most allow for the rapid flow of cooling water through the system for its protection from Thermal Damage at the intersection of hot R.M.H.
and plumbing, and must do all this during a power outage !

I understand how the Milkwood system works, as built, there are no valves to inadvertently be closed. The Geof Lawton system is nearly identical, listen to his analogy of burning
the tea kettle dry at 10:00, Due to steam loss (see below ) this is a hard system to move indoors, to live safely with this system indoors you would want to pipe the steam outside
and have a sight glass that gives you an instantaneous check on the level of water in the 44gal drum# And a large vent that could not get blocked by a collection of mud daubers

In Mexico there are hotels full of retired Americans and in every bathroom there is a wood fired water heater, a Ra'pedo, which looks very similar to a natural gas/L.P.G. hot water
heater, and you build a fire in the bottom where the gas burner would go, there is a simple valve that you open to fill the Ra'pedo tank and then shut off ! This simple valve system
allows the pressurized side of the system to be isolated from the Ra'pedo, which is open at the top preventing any pressurizing of the system, much of the year a ra'pedo makes
for a nice toasty, slightly steamy bathroom 1st thing in the morning!

As much as 5 months of the year it turns the bathroom into a sauna ! The room I stayed in, had no plaster on the ceiling as the Ra'pedo had overflowed in the room up above
ether to failure of the valve or expansion, or operator error, almost all of the rooms in the 'Pensonair hotel' I stayed at had plaster patches on the bathroom ceilings ! Again these
are very hard systems to move indoors, while greatly reducing the dangers of 'Squish-Boom' a Failure indoors with this system could be very expensive - I would not expect any
sympathy from an insurance inspector who comes to do an appraisal, in fact I would see a cancellation of any existing policies in your future !

Consider any one of the other systems and I can't see enough of the plumbing to have an opinion, before I wanted to duplicate these systems I would want second and 3rd opinions
on the way it was plumbed. I would also want a boiler grade high temperature/high pressure relief valve, and an automatic mechanical-only water 'volume/level control to
supply makeup water to my system. Oh yes, and a bypass water feed valve just for emergencies !

Consider just two possible valve and human interactions, first consider the presence of a simple valve stem leak in a half inch 1/2'' valve with a common replaceable faucet washer
located inside the valve and on the supply side, The home owner discovering the leak has tightened down the 'packing gland' to try to stop the leak-''damn I have tightened the
valve stem packing down as far as I can get it, and this thing is still leaking!'' He takes a very quick shower, shuts of the water supple and makes a mental note to replace the
packing, or more likely the same valve, any one who continues to use the Rocket Mass Heater R.M.H., now has to deal with a pressured system, and after the boiler pop off valve
does its thing, there is the possibility of damage to the plumping from excessive heat from the R.M.H. !

Take this scenario 1 step farther, our hero knows exactly what kind of valve he wants to buy to replace the old valve, he picks one up at lunch and gets a new propane tank for his
torch , sure that he made note that he had all of the rest of the supplies needed left over after his last job ! Our hero now goes home and even though He has to reach around and
through some small tight places is able to install/'sweat in' the Valve !

Our hero neglected to make note of the arrow stamped on the side of the valve and inadvertently installs it backwards, but when He opens and closes the system to check for leaks
the system seems to work fine with no leaks, - time passes, due to a failure at the factory to use 'locktight'* to secure the screw holding the faucet washer in place, now temperature
fluctuations and vibrations from a water hammer causes the screw to back out and get lost !

Our Hero's wife notes that the water coming out of her faucets are too damn hot, and not wanting to let the pop off drain down the system, decides to cap the R.M.H.s feed tube to
starve it for air, putting the fire out, and attempts to open the reversed valve to allow more water and then goes to fill the washing machine,laundry sink, kitchen sink,maybe a tub.

Unfortunately, because the valve was installed backward, and the screw fell out, instead of the flow of water lifting the faucet washer off of its seat the water pressure now holds the
Faucet Washer down on its seat, allowing only as much water to pass thru the guts of the wrongly installed valve as can piss through the hole in the faucet washer where the screw
was supposed to pass in securing the washer in the 1st place !

These scenarios are more likely than 'squish boom' and can result in major damage to both your system and your house, But they point out why such a system should be installed
by a professional, and that raises the question where would you find a pro with experience in a new system, in our case I would want to go to a person who had actually installed and
used a system with Two inputs, at this time the only double inputs are Geothermal, and Solar !

* No one that I am aware of is using lock tight on the screw that holds the faucet washer in place, I have lost track of the valves I have seen installed backward, or the exact number
of backed out / lost screws/faucet washers? 4? 5? and I have only found just one reversed valve with lost screw installed on the water supply side of a boiler, but if I have found one,
'Murphy's Law' says there has to be more !

# The 44 gal drum is actually a 55 gal drum, The Australians still measure Fluids in Imperial Gallons which contains 5 quarts to our 4 quarts !

For the Good of the Craft! Think like Fire, Flow like Gas, Don't be the Marshmallow ! As always your comments and questions are solicited and Welcome ! PYRO - Logically Big AL !

@ Allen

Lets assume we install one of these bad boys outside but quite near the home/building but was feeding an indoor hot water tank. Would I be right in saying that the hot water tank would be totally safe indoors?

It's not the distance from the boiler that determines if it is safe... a steam explosion near your house vs. in your house would be better but not by enough to notice.

What Allen is concerned about is that steam and really the steam pressure. If the heat applied to the water (in the tank, the pipes, the whole system) gets high enough that the steam pressure gets high enough that something has got to give then you will have problems.

This is true of any heated water in a sealed space... and sometimes even in places that aren't sealed if the heat (and therefore steam, and therefore pressure) can build up quicker than the release can let it out.

The way this is dealt with in most standard plumbing is 1) control over the source of heat so that it doesn't exceed certain temperatures 2) safety pressure release valves to "blow off" dangerous pressure and sometimes even 3) the ability to rapidly stop the heating system in the event of an emergency (shutting off the gas, etc.)

So whether your RMH boiler was outside or inside you will still have to consider those issues. With some added difficulty.

1) RMH technology is "on" or "off" which means the system will be very hot for a certain amount of time and then "cold" at least in the burn chamber. So you can't throttle it back to protect the plumbing or reduce the pressure.
2) Any part of the plumbing which would collect heat beyond safe pressure tolerances will need it's own pressure safety blow-off valve, and probably one tuned to fairly low pressures just to keep things safe as possible... which does lead to the situation where the pressure rose, the valves blew, the system drained or bled out all the water and now you are cooking your plumbing with the heat from the RMH.
3) It is impossible to simply stop a RMH, especially if it is of any considerable size. So the design needs to be safe in spite of an inability to "stop" the heat. Often by some kind of system designed to rapidly cool the RMH the plumbing, or both.

Now with the safety stuff on the table to think about, and I do hope you are properly scared there are some ways to approach these issues.

A relatively small burn system with a relatively large thermal mass. - This is pretty much what Geoff exhibits in the example of his big drum water heater.
The good: short burns with low amounts of fuel heat the system with little to no possibility of being able to blow off so much steam pressure that you would run into issues of explodey pressure or issues where the water boiled dry. As long as the person running the boiler understands they occasionally have to top off the water level and they cannot burn in this system constantly if the hot water isn't being used you would be ok.
The bad: The operator has to understand the system and can accidentally force the system to fail. This may not be an issue if you were the only one who would run the RMH, you didn't worry much about code issues, or you were trying to bring hot water into someplace where it was impossible to get any other way. In most circumstances there are better, safer options to the overall design.

A relatively large thermal mass with relatively low temperature water - A large bench system which heats up a great deal of masonry with a design that limits the temperature of the plumbing by keeping it away from most of the heat.
The good: No need to worry about the system, if you're cold you burn the RMH, the mass works it's magic and because your design keeps the plumbing within safe tolerances once it's installed you probably won't have to worry about it much.
The bad: Until you've played around with this a little bit your plumbing will end up too close (and therefore could still get too hot) or too far (and therefore never get hot enough) to the heat. This is where knowing the plumbing and knowing the RMH technology really helps. If you hit the sweet spot or even are just a bit on the cooler side you could use the warmer water being produced to preheat your conventional water heater or forced hot water heating system.


You can choose to have a system that requires knowledgeable supervision, provides great fuel conservation, and (relatively) high water temperatures,
or you can install a system that doesn't require direct oversight, provides excess heat (not used for hot water production I mean, but if you're heating your house/seat it's hardly a waste), and lower water temperatures.

Considering where this thread started, a greenhouse heating RMH with a low water temperature output preheating your home house water probably wouldn't be too bad, and with the right safety valves in place, erring on a design that keeps the water temperature lower (safer) you could get an awful lot of work out of that system.

Jason Matthews : Let me try to answer only the last question you asked, If we are talking about a normally unpressurized system like Geof Lawton's, or Milkwood's, then we
are talking about a vented hot water tank with many feet of 1/2 inch or larger copper coil inside to absorb heat out of the tank, average exhaust gas temperatures inside the 44
gal barrel will be around 500 F, both the Milkwood and the Lawton systems are dependent on loading the safe amount of wood into the Rocket Mass Heater R.M.H. for 1,2, or
more showers with the make-up water being added between each shower!

Then, if I understand what you are saying, you are asking if you could then deliver the water from the copper pipe directly by running more copper into your house to a second
indoor water tank, I would reluctantly agree that water could then be drawn from that second tank to provide hot water for Cooking, Washing and Clothes Washing, but only
with a tempering valve* that mixes very hot water with a supply of cold water between the 2nd indoor tank and faucets which would decrease the temperature of very hot water
down to a safe temp.

To guarantee that you will have enough hot water to do a personal shower, fill a couple of stock pots with hot water for cooking, and two loads of presorted washing and always
remembering to do them in order, 1st Hot wash with warm rinse, 2nd warm wash cool rinse will only come with practice and experience relating amount of wood used on a cool
day low humidity to the amount of wood used on a hot muggy day ! I expect that You ,Me, or Mike, might just have different learning curves for learning to fuel our R.M.H.s.
There would also be a difference between R.M.H.s and also within a just cleaned Rocket and a Rocket needing cleaning

So let me turn this around and ask you, knowing as much as you know right now, how would you go about writing a safe operations check list for operation of your shower so
that both Mike and I could safely use your heater to take a simple shower ! it is also important to get the opinion of any significant other also !

Once again I go back to suggesting you study a combined system like Electrical heated hot water and solar, or gas and geothermal/heat pump! We have a whole Forum Thread
on Solar, and a little searching with Google should allow you to find a diagramed plumbing system from a commercial model that a H.E.V.A.C. Engineer has signed off on !

Think like Fire!, Flow like a Gas!, Don't be the Marshmallow ! As always, your Comments and Questions are Solicited and always Welcome ! PYRO - Magically BIG AL !

* this type of mixing valve is wholly mechanical in function, while it can be fouled by hard water and mineral deposits I would only use this type of mixing valve ! A.L.

Thanks Mike and Allen for the detailed answers.
Much if this is very new to me and with zero knowledge of plumbing much of its it is lost on me as well. Maybe with further development the Boom Squish might become a thing of the past?

allen lumley wrote:
So let me turn this around and ask you, knowing as much as you know right now, how would you go about writing a safe operations check list for operation of your shower so
that both Mike and I could safely use your heater to take a simple shower ! it is also important to get the opinion of any significant other also !

I think I'd ask everyone to sign a disclaimer!

Does anyone think RMH's will ever be made by a large company as a mainstream consumer heating device, or is it likely to be one for the enthusiasts only?

Jason M : This is exactly why I said that this would be a 5year project, we have to have a group of people who see the need,and want the product before the 1st model is made!
We also have to find that group of people who are willing to 'OWN' the idea that it is their responsibility to 'run' a Rocket Mass Heater safely and train them to do it !

If your point of contact for your hot exhaust gasses / copper water coil was merely some small distance down stream from the Rocket Mass Heater, within the Thermal Mass
bench you could have room to install your Doomsday device, when your water was in danger of over heating, this would be the simple by-pass that lets you send all of your hot
exhaust gasses directly to your vertical chimney !

Now remember we made this installation with a primary mixing valve co-located near the indoors storage tank to make sure that we were not lying on the floor of our shower
being scalded to death, this event happening just before our over-fed R.M.H./ water heater flashes to steam, 'Bang - Squish' DAMN i'm going to sell this Idea to Steven KING !

So, if we could design a safety control that would mechanically sense the over heating of the water coils and rapidly shift the by-pass from one setting, all heat going though the
Thermal Mass Bench, to all the heat going up the chimney - - ( remember this system has to work in the dark with the power off/out Every Time!!! )

Now let me turn this around on you again, if this was a commercial product, would you buy a system that might or might not send all the heat for your shower water unexpectedly
up the chimney and not to your water heater? As a salesman how many people do you think you would need to approach to sell just one Water-Rocket ?

Again, I mention a dual heat source system. You might be able to create a R.M.H.-Thermal bench system that heated your whole house and supplied warm water to be mixed
with hot water from a second water heating source so that 80% of your total cost of heating water was born by your Water-Rocket system, I expect that someone working within
the Solar or Heat Pump communities will work out a system that works safely for him/her but, what would be his motivation to offer this design out there for the general public to
miss-copy !

Two final thoughts the safe Fusion Reactor is 50 years away, and has been for 67 years ! A week ago yesterday I was at a Campground near Kennibunk Maine, standing in line
to use a shower that gave about 10 min of hot water for a Quarter. Guess whose shower 'broke', guess who didn't get a shower, guess who isn't going back to that camp ground !
For the Good of the Craft. Think like fire, flow like gas, Don't be the Marshmallow ! As always, your comments and questions are solicited and welcome ! Big AL !

@ Allen. Yes it might be a tough sell! It's hard to know what the statistics would be for Boom Squish fails if lots of people had these water heaters, either in their current or more advanced form.
They could even be more safe than gas - who would want that in their house after seeing this bad boy?

http://www.youtube.com/watch?v=ap02Gnq5LKU

Jason Matthews : Yes exactly, think Boston Marathon Bombing only with fire and many more second and third degree burns!

The Mythbusters set up a electric water heater to over heat and flash to steam, hunkered down behind their clear plexigass blast shields-
the tank ruptured destroying their building, after they had been wandering around for over 20 sec looking at the scene, the remains of the
hot water tank came back down ! You can find the whole thing copied to you tube in several places ! Big AL !

Mike Leo wrote:Sometimes you don't want to heat the whole house, just enjoy a bit of fire or heat up a cup of tea. That bypass would almost turn your Rocket Mass Heater into a Rocket Stove with a simple built in adjustment.

Also, even during the winter time, as Erica mentions in the video activating that bypass "reduces drag" which you can translate to "improves draft". Especially during starting the RMH having a better draft will keep things cleaner, get the rocket to operating temperatures faster and basically improve a lot of the experience.

I am going to start a new thread about this for clarity as I want to ask a related question to this.