First Rocket stove heats water with pics

I bought the book and now it is time to built my first RMH. I finally completed it and the pics are here.








My RMH is a 6'' system i can cook on and its hooked into my conventional stove to bake in and the bench runs through my house about 20ft and at the end of the bench i have a 50gal used water heater inside the mass bench to heat the water. I do not have the hardware to test RMH core or 55gal top temps but i do have the ability to get test up to 450 degrees and i am getting 350 degrees out of the exhaust of the bottom of the 55 gal barrel and 180 degrees at the last bench inside and i am guessing close to 100 outside or less since i can touch and hold on to the outside smoke stack.

My RMH is built with two propane tanks welded to together for the feed chamber. the bottom of the feed and burn chamber are made with perlite and refractory cement. My heat riser is made with a 6'' tube inside and a 10'' tube outside with perlite and refractory cement filled in for insulation with a 2'' gap between top of 55gal drum. It is a very heavy unit but i did put commercial style wheels on the bottom that allow me to move it around and plug back into the oven or bench mass system.

The dragon is not the fastest start up but then i made an easy start up fan to boost a sluggish dragon and cold starts with a 6'' stove cap and a computer fan and 9v battery, but once it gets going its amazing.

I put the water heater at the end of the line because the stove pipe exhaust is the coolest at that point and does not exceed 180 degrees. it does help heat the water tank but does not heat it up as fast as i would like it. basically an all day fire with min heat up is not the most efficient water heater but never the less it does warm it up safely with out chance of steam dangers.

* any suggestions on a better way to heat water fast/better is welcome. maybe a gravity convection self circulating pipe inside the exhaust pipe to a tank?

The Feed chamber has impressed me in that i have put at least 8'' full size logs in and have burned for many hours. I designed the RMH feed chamber this large so i can pack it full of wood and forget about it without having to fool with it every half hour or so. i can pack it and let it burn for hours. Its does so amazing after packing it at 11pm before bed i woke up this morning with a pile of hot embers in the bottom and came back to it at 11am and still had enough to restart the dragon up again which is so impressive to me for my first build.

* The only problem i have is steam turning to water in my stove pipe and pooling inside the pipes. i have to figure out how to address this before it rust out the pipes in the future.

My pipes are standard galvanized air duct with cinder blocks built as the walls around the pipes and packed with dirt and then topped with cement for durability.

I will graciously take any constructive criticism on how to deal with my water condensing issue in the pipes would be humbly accepted.

* those are my only issues and welcome help. Thanks

Condensation in the ducting is a common occurrence in a new RMH. It generally goes away after the mass is thoroughly dried out.

Loose dirt around your duct is likely to be more insulating than conductive, and you may not be getting as much heat storage as you could. The water tank at the end of the bench is probably helping here, absorbing the greater than normal leftover heat.

I wouldn't put a water coil anywhere closer to the heat source than you have, for safety. But you may be able to do that right next to the tank to increase the absorptive area.

If you are getting a full load of wood burning for many hours, you are likely not getting as efficient of a burn as you should. Can you try whiffing (carefully) the exhaust outside? That is not a true scientific test, but might show a basic idea of how good your combustion is.

THank you for the reply and help.

a full load of wood is about 2 square feet of wood with pieces as large as 8'' logs that are two propane tanks in length. To me hours of burning of that much wood does not seem out of the ordinary since i designed it to have a extra large feed chamber so i did not have to load each individual piece every 15 min to half hour.

the condensation only forms when the rocket is in use and it pools in my pipes. will this rust out my pipes? if i would have known this was going to be a problem i would have made sure to configure the pipes different. i need to do something im afraid it will cause problems (rot wooden floor, rust pipes... ect.) none of this happened when i tested it.

the exhaust out side is almost pure steam when the RMH is in full dragon speed. i have felt the exhaust and it is very moist air.

i would really like to get the water heated better. if you had a pipe running through the exhaust and then to a water tank, would the water move up towards the tank as it gets heated and then have a loop where the cooler water that goes under the house and back to the other end through the exhaust pipes again in a loop circulate on its own? does heated water rise and cold water sink causing a looped system to constantly circulate? does anyone know enough about boilers and math to know if this concept will work?
knowing that the basement is 55 degrees all year round would this looped concept work to keep the water from boiling circulating on its own with no pumps?

Fade style, your bench looks like it coated with cement? I thought cement would not endure heat and should not be use on RMH? What kind of cement did you use and how to mix it.

The 50 gal water heater tank, how hot could you be able to heat the water up to? Do you have gut pictures of how you did the water tank in the bench?

"regular" cement was not used in the high heat areas of the heat riser and burn chamber. "regular" cement can handle the low bench temps without spawling or cracking. i built the unit per book style specs and only went off reservation with the extra large feed chamber and water heater tank at the end. i tested the unit out side and inside before finalizing the unit.

i am sorry i should have taken "gut" pics but i did not. the exhaust pipe runs right beside a 50gal water tank on its side and one ten foot section of copper pipe wound around the area of exhaust pipe at the front of the water heater near the stove cap in the water heater bench pic.

so far i think i have managed to get the 50 gal of water up to about 70 or 80 deg which is double its temp coming out of the ground is about 40 deg. our water is cold out of the well and or spring.

here is a cheap simple mechanical drawing of my RMH

What you have is not actually a J-tube; it is an L-tube with added wood magazine inline. If you keep the magazine capped tightly all during the burn, you can be safe, but never ever take the cap off while the wood is burning or you are likely to get a flash of flame rolling out of the top from woodgas meeting fresh oxygen. This seems like a kind of gasifier in effect, and if it actually works that way, you may be getting good combustion.

It seems that you are missing the whole point of a rocket mass heater, which is to have a fast hot fire for a relatively short time, which stores the heat generated for later slow release. There is no reason for a RMH to burn for many hours at a time, unless it is grossly undersized for the heating load and needs to struggle to make enough heat.

You don't give any information on your climate, or the size and condition of your house, or what area you are actually trying to heat. This is important for determining how big a system you actually need. You have 20' of duct running through mass benches; are there any elbows in this? What kind of exhaust do you have? A real chimney, or just a short stovepipe, or??


The water loop you show would definitely circulate as planned, but you would essentially be using the heat to try to heat the basement, which is pointless. Just circulating from the bottom of the tank horizontally and rising through the airstream will function without throwing heat away where it will do nothing for you. If you do have a water tube in the airstream, you absolutely need a pressure relief valve even if you are far from the high heat area; you don't know how hot the later end of the duct will get after a long burn. This is still not truly safe, and I would not recommend you do it unless you have a trained professional install it or okay it. The only safe way to heat water with a woodburning appliance is in an unpressurized vessel with venting open to the air, or a system designed by a professional with all the safety bells and whistles. Your whole tank at the end of the mass is far enough from high heat that it is pretty sure to be safe.

Thank you for your reply. "What you have is not actually a J-tube; it is an L-tube with added wood magazine inline."

Im not here to argue or split hairs as to the "definition" or type of RMH i have. I have been calling it a "J tube" with an over sized feed chamber with an access port since the "access port" was an add-on after thought at the last moment for ease of lighting, cleaning and or loading.

"never ever take the cap off while the wood is burning"

that is how i load my full bank of wood to burn for many hours.

"This seems like a kind of gasifier in effect, and if it actually works that way, you may be getting good combustion."

You are correct, i get amazing combustion. until i design some lid hinges for my "inline wood magazine" there is a technique to opening the lid without any flashes. i kinda crack it and roll it off and throw in the wood. stuffing it wide and deep.

"There is no reason for a RMH to burn for many hours at a time"

the way i read all the material including the book i bought. Burning in the RMH for 2 to 5 hours a day is normal depending on size of house and insulation and climate.
2hours is a couple 3 is a few and 5 is many. I can load my "inline wood magazine" completely full even logs as large as 8'' so it can burn for 5 (many) hours. I have been testing the capabilities and i can start a fire in the evening with an extremely large log and there will be embers in the morning so i can start another small fire and there will be embers for the evening fire and if i can keep it down to two smaller fires so i can use the embers to start it back up i then need less lighter fluid/matches and or other small fire starting resources. i am poor so lighters arent cheap if i have to use that as a starting resource and rubbing sticks together are out of the question. My baby dragon roars and is designed to cook on and bake with so a large dinner may need many hours to bake with regardless if the house is warm or not. my needs and desires are not to conform to everyone else and i dont want to fool with a RMH every 15 to a 1/2 hour so i built it to MY specs to do what i want it to do and i want to be able to stuff a gigantic log in to my burn cham...er i mean "inline wood magazine" here is an 8'' sucker i just stuffed in and i plan to jam in a 10 incher next time to see if she can handle it all. she has a wide deep throat and i pan to fill it.



"You don't give any information on your climate, or the size and condition of your house, or what area you are actually trying to heat."

my climate is 6b my house is nearly 1000sq ft and the house is a drafty old cabin and im trying to heat the whole house, cook with it, bake with it and heat my water with it so if it burns many hours that seems very exceptable for a RMH workload and it still uses less wood than my conventional wood stove including a larger work load and all the while burning with less smoke.

"are there any elbows in this? What kind of exhaust do you have?"

I have three elbows and a twelve foot smoke stack that goes higher than the roof using standard galvanized 6'' duct.

"you don't know how hot the later end of the duct will get after a long burn."

the temps i stated in my first post are after a full day burn and maxed out and sustained and no matter how i stoke, blow and push it the dragon growls at those sustained temps. i wish i had a way to test the internal core. my barrel does get cherry red at the top and the sacrificial 6'' has flaked into pieces internally. if i did use the "circulating" water system it would be placed in my middle section i did not post pics in my first post of between the two elbows and an entire bench away from the RMH fire source. the temps in that tube max out at around 220 at one end and 180 at the far end and all safety features would be put into operation and i am very capable of doing it "professionally" and can "okay" it my self.

here is a pic of my middle section mass bench


thanks for your advice, concerns and opinions. i will take them all into consideration.

I dont know about yall, but i seriously do not want to or enjoy spending time splitting wood into tiny little slivers to put into my dragon. i mean why would i do that when you can build a larger "inline wood magazine" and shove full size logs in it to have it burn for hours. burn longer less work = more time to do other things you enjoy and more affordable.

Glenn says "never ever take the cap off while the wood is burning"

here is my operating proceedure with my rocket mass heater. start small fire and then pack it full of wood. once packed, there is no reason to lift the lid until it needs more wood. here is a video of my RMH in opperation just before i put in more wood... mind you its a 6'' RMH system the whole way through except with an 11.5 inch WIDE and almost 2' deep wood feed chamber. 1 full feed chamber is almost 2 square feet of wood and in most cases that is all you need to burn and never need to touch it again unless im trying to cook, bake, heat water or an extremely cold night. in this video you will see wood burning at the bottom of the feed chamber with both access port and feed chamber lid off and it still has such a powerful draw there is no smoke or flash as Glenn would think. now it would be stupid to open the feed chamber lid when full... but then why would you need to open the lid? if it needs adjusted usually you can poke at it through the access port and one of the many reasons why i put it there...

RMH VIDEO RUNNING WITH LOW WOOD LID OFF

RMH VIDEO RUNNING FULL LOAD LID OFF that should be anywhere from 1 to 1.5 square feet of wood in there if i burn two of those a day its anywhere from 2 to 3 square feet of wood a day, depending on RMH workload needs. that pic of 1 to 1.5 sq ft lasted 5+ hours and burned with increased velocity as the wood burned down without touching it one time and the house is a comfy 72 degrees inside and 30 outside.

both videos show operating my RMH with low wood and a fully loaded feed chamber with both lid off and access port open.


* Questions and ideas i would still like to hear from others is what to do about condensation and water heating solutions? any thoughts? we can bump ideas together an come up with something.. . there are a lot of smart people on here.

I salute your superior building and operating skills. Seriously. We see so many builds trying to do the kind of thing you are doing, and they most always fail in one way or another. That's why we try to discourage such things for indoor use. You can't count on random people operating safely, either. You have trained yourself to handle the wood feed in a safe manner, but if you had a visitor you would probably need to be wary of letting them near it. The standard designs have been developed to be relatively foolproof, as in fools can't easily do great harm.

A 1000 square foot cabin sounds about right for a 6" system, and being leaky explains burning for so many hours.

Your original description sounded like you were only getting about 450 F on the barrel, but glowing of any sort is at least 1000 F, which is as hot as you ever want to be running a system. How did you determine the 180 F at the end of the mass? Is that a surface temperature, or the air inside? If you have hot water system experience to build a heating coil safely, again you are ahead of the vast majority who we don't want to try this because they are likely to injure or kill themselves.

If you want to make a water heating coil in the duct run, I would advise using as large diameter copper as you can to avoid instant steam flashing. This will not be as efficient of a heater but will be safer. Eliminating any valves in the loop from tank through coil will also make it impossible for someone to accidentally shut off circulation.

*** EDIT *** ALL ABOVE MENTIONS OF MY AMOUNT OF WOOD BURNT SHOULD HAVE BEEN NOTED AS CUBIC FEET AND NOT SQUARE FEET.

i am humbled by your compliments and i feel after much research and testing i have failed in a small manner to meet 100% of my goals to be able to heat my water faster at a higher temp and not seeing in the book or other research info on the need to deal with this much condensation pooling of water in my exhaust ducts is a bit disappointing. i am tempted to bust out a bit of cement wall to fix the issue.

"How did you determine the 180 F at the end of the mass? Is that a surface temperature, or the air inside?"

I have an "oven thermometer" that goes up to 450 degrees. i placed the oven thermometer in each section of my system inside the exhaust duct. at the base and exit point of my 55 gal drum after the exhaust has expanded and cooled inside the drum and is entering the main exhaust duct line i get 350 degrees. then i measured inside the duct at the end of the first mass bench entering into the 2nd mass bench and i get 220 degrees. then i measured inside the duct at the end of the 2nd mass bench entering into the last mass bench with the water tank inside at 180 degrees and the outside measurement was touch only and it was only warm to the touch.
do those temps seem normal for a 6'' system? does it seem i am getting enough heat absorption into the mass by my description?

i am debating a bunch of solutions in my mind and will figure one out.
i am seeking suggestions on the subject of:

*water condensation in the pipes pooling.
*faster and higher water heating.

as ive stated earlier your compliments and suggestions are humbling and graciously appreciated.
"That's why we try to discourage such things for indoor use."
look Glenn i am giving you the benefit of the doubt that you have good intentions in mind but the imperious ninny tone does not sit well with me. i am a straight forward guy that expects people to succeed or fail by their own means and thats the part of that freedom which comes with responsibility and if someone wants to do something uninformed and uneducated its completely up to them. people opinions suggestions are one thing but sounding as if you are part of a board of RMH permission giving governance rubs me the wrong way.

"you would probably need to be wary of letting them near it."

thanks for the advice but i am sure i am big enough boy to "okay" who i let "near" my stove.
may you prosper in all you do Glenn.

Remember that probably thousands of people will read this thread in the future, and some will be wanting to do all kinds of experiments without fully understanding the risks, or knowing how to be safe. If we don't give warnings regularly, some will think they can go and do something that will injure them while thinking "I saw it in x, it must be okay..."
That happens all the time with youtube videos of people making what we know from experience will be bad mistakes, and others copying them and coming here to say "why doesn't this work, I saw it on youtube?"

My permies forum member in common, this website is surely NOT a website of "discouragement" but a website of knowledge and collective experiments and thousands and thousands of trials and errors both good and bad.

"Remember that probably thousands of people will read this thread in the future, and some will be wanting to do all kinds of experiments"

I am one of those "thousands of people" and i made a huge mistake (to you it may seem small but im a perfectionist in some ways and feel its a big problem) with the condensation issue and i only wish i had read this in the book or in my other research that it would be this big of a deal. so my big mistake is now out in the open and others will know about it and it is a big deal that needs to be addressed while building your mass benches. i should have configured it to lean all in one direction with the seem up and in the direction of the connections so the condensation can drain in a desired direction instead of pooling. Now i am part of the collective experience for others and not a ninny telling others what to do but providing them the info of my experiences so the next guy can make informed decisions on his own.

"some will think they can go and do something that will injure them while thinking "I saw it in x"

freedom not only needs responsibility but it is also dangerous. i want and will defend my dangerous freedom in that i decide what is good for me as long as i dont hinder the liberty or property of others. each individual is responsible for THEIR actions and can not use the excuse "i saw it in x" to avoid responsibility. if you jump of a cliff just because you saw someone else do it thats your own dumb fault. make your own decisions and fail or succeed by them. thats the problem with this "millennial think" we have now in this country that i feel has been a bit contagious and is spreading to others and that is lack of self responsibility. if you chose to do something it is best to be informed in the best way you can.

"That happens all the time with youtube videos of people making what we know from experience will be bad mistakes, and others copying them and coming here to say "why doesn't this work, I saw it on youtube?" "

even though i read the book this is basically exactly what i did and what this forum is for... to get informed and gather from collective experience here and i love all of you for the hard work and experience you have shared.

conclusion: I am not here to debate responsibility of others and what permissions you should or shouldnt do. I am here to find answers from the collective knowledge base for my problems and share my experiences.

*i need a solution for a large amount of condensation pooling in my exhaust ducts
*i would love to hear from all the RMH folks ideas on water heating solutions. please post ideas and solutions.

How hot does the last bit of cob get, on the outside and near the duct? Can you tell where the water is condensing? If your exhaust is still 180 F as it exits the last mass, that is probably above the dewpoint no matter how humid it is. If the inside of the last duct is cool enough to condense water, that would be what is happening. Is it possible that the condensation is happening in your chimney and running back into the mass? How well insulated is the chimney? Is the ductwork level, or where are the high and low points?

How hot does the last bit of cob get, on the outside and near the duct?

warm, but im not sure how to get an exact measurement.

Can you tell where the water is condensing?

i can not see where it is condensing but i can see where it pools.

If your exhaust is still 180 F as it exits the last mass

i have not measured it but it is only warm to the touch outside and i do not have it insulated on the outside. i am thinking about lining half my stack outside with concrete.

Is it possible that the condensation is happening in your chimney and running back into the mass?

i had not thought of that, possible i will check it. not sure i would be able to sit an watch steam condensate... i guess kinda like watching grass grow but i will see if i can see something. water droplets dripping from inside of stack maybe?

How well insulated is the chimney?

its not at all on outside.

Is the ductwork level, or where are the high and low points?

i followed most peoples work and most people said it was not rocket science (no pun intended) when leveling the duct work so i eyeballed it as best i could. there are a few low spots but nothing dramatic. only slight variations it level. i have a pretty good eye. i think some of the low points happened when i was packing the dirt in around the duct work. i packed it pretty good to eliminate air pockets.

Here is a video of a full size 8'' x18'' log feeding the dragon with the lid off and access port open with no smoke.

Here is a pic of the 10'' wide log i gave my word i would put into the dragon.


My custom built RMH has exceeded my expectations in almost every way except for the water. i had conceived the idea of being able to put a full load of wood in including a fewer larger than sliver split pieces to pack into my 6'' system but did not think it would be able to handle a full sized 10'' wide log and burn for many hours just impresses me. i have noticed that burning these large logs 6'' or wider significantly increases the burn time allowing me to have left over embers for the next days burn and easy restart. by loading the feed chamber full of very large logs, keeping the air tight lid on and access port open i have noticed that the heat from the dragon super heats the wood in the feed shamber turning the wood into charcoal as it sucks down and burns the gasses off the wood and then finally the charcoal collapses and tuns to embers as it completely consumes except for the tiniest ember pieces buried and insulated by the ash for the next day and easy start.

*still disappointed with the condensation and water heating though.

I live in Alaska with temps in winter usually down to minus 50 or 60. I've been heating water with a wood stove in my house for 40 years now and usually have plenty of free hot water all winter. I have about 20 feet of 1/2" OD copper tubing right in the fire box and it circulates to the hot water heater upstairs. No pump, it circulates by itself, but if I start the fire from cold I have to not get it hot real fast or it pops and snaps till it gets to circulating, then it doesn't matter how hot the stove gets, it just makes the water go faster and heat the tank sooner. So I am sure you need more copper tubing and in a hotter place to get enough hot water. I know about all the warnings about the dangers and plan to change things nest summer, but don't consider it an emergency now after 40 years.
That brings me to my other system I have in my airplane repair shop which is a stove made of a 30" x 42" pipe with if I remember right 50 feet of tubing and it circulates to an open 30 gal. tank sitting on top of the stove. Another 60 feet of tubing is in that tank and circulates to the tubing in the concrete floor. I'm out of time now, have to leave. But want to say a little more about it later.

If your exterior chimney is uninsulated, that would absolutely be where the condensation is happening. It will also cool off immediately when the fire peters out, so you would get no draft without the strong heat source. Replacing the chimney with an insulated one, or if budget is tight, adding section by section an 8" duct jacket and packing it with perlite or rockwool (joints arranged to shed water to the outside and top edge capped off to keep the insulation dry) should make a big difference in your condensation and in your ending draft.

I would also put in a drain vent to let any water running down the chimney drip outside instead of continuing into the mass ducting. A T fitting at the bottom of the vertical chimney instead of an elbow will make this easy.

Phil Holbrook wrote: I live in Alaska with temps in winter usually down to minus 50 or 60. I've been heating water with a wood stove in my house for 40 years now and usually have plenty of free hot water all winter. I have about 20 feet of 1/2" OD copper tubing right in the fire box and it circulates to the hot water heater upstairs. No pump, it circulates by itself, but if I start the fire from cold I have to not get it hot real fast or it pops and snaps till it gets to circulating, then it doesn't matter how hot the stove gets, it just makes the water go faster and heat the tank sooner. So I am sure you need more copper tubing and in a hotter place to get enough hot water. I know about all the warnings about the dangers and plan to change things nest summer, but don't consider it an emergency now after 40 years.
That brings me to my other system I have in my airplane repair shop which is a stove made of a 30" x 42" pipe with if I remember right 50 feet of tubing and it circulates to an open 30 gal. tank sitting on top of the stove. Another 60 feet of tubing is in that tank and circulates to the tubing in the concrete floor. I'm out of time now, have to leave. But want to say a little more about it later.

this is amazing information. do you think my water tank diagram design will work then? how much copper do you have in the "firebox" how hot does you firebox get and is your system open or closed system? my diagram to heat water is a concept i would like to add and the copper will be about 10' long inside the exhaust duct 220 degrees at one end and 180 at the other end and circulating up inside a tank outside of a mass bench. should i keep the copper line there or should i move it closer to the heat?

Glenn Herbert wrote:If your exterior chimney is uninsulated, that would absolutely be where the condensation is happening. It will also cool off immediately when the fire peters out, so you would get no draft without the strong heat source. Replacing the chimney with an insulated one, or if budget is tight, adding section by section an 8" duct jacket and packing it with perlite or rockwool (joints arranged to shed water to the outside and top edge capped off to keep the insulation dry) should make a big difference in your condensation and in your ending draft.

I would also put in a drain vent to let any water running down the chimney drip outside instead of continuing into the mass ducting. A T fitting at the bottom of the vertical chimney instead of an elbow will make this easy.

that is also very good info and i will take that advice. i do have a T at the up point to the outside stack and i will look at adjusting it or vent it. i plan to "jacket half the outside stack in concrete and do the rest with a 8'' duct jacket lined with insulation. thank you all for you amazing info.

***UPDATE*** I humbly took Glenn's advice and check my outside T and made sure it was slightly tilted and "vented" and now i do not have any condensation in my exhaust duct. thanks buddy.

My next deal is to install the idea i had unless Phil can give me some better advice. i respect Phil's 40 years of experience.

*** Phil Holbrook

can you please draw up a diagram of your water heating system and post it please? how hot is your fire box an dhow much copper do you have in your firebox?

I gave my word i would post a video of the 10'' wide log going into the mouth of my RMH to feed the dragon and here it is. I had to practically jump on the log to push it down into my feed chamber it was so wide. i did have to close the access port this time to increase the draw and there was a few puffs of smoke while the lid was off.

Take note i posted the 8'' log video above. i shoved that 8'' log into the system a little after 1pm and i am now just putting in the 10'' log. WOW! yup thats about 6 hours of burn time with an 8'' log. i should get at least 6 hours plus with this 10'' log during this test.

Yes my house is hot as hell while im doing these tests but these tests need done so i can share with everyone. thank you to all those that helped and i hope to hear from phil soon.

RMH video of a 10'' wide log burning in the mouth of my dragon with lid off and access port on.

F Styles wrote:

this is amazing information. do you think my water tank diagram design will work then? how much copper do you have in the "firebox" how hot does you firebox get and is your system open or closed system? my diagram to heat water is a concept i would like to add and the copper will be about 10' long inside the exhaust duct 220 degrees at one end and 180 at the other end and circulating up inside a tank outside of a mass bench. should i keep the copper line there or should i move it closer to the heat?

I can't tell just how your tank is situated but I think as long as it is higher than the heat source it will circulate by itself, hot water rise and cooler water sink back to the stove. But I'm just sure that 10' of copper tube is not enough nor the temp hot enough where it is. I think you're enough of a do it your self guy to put that tubing where it's way hotter and test it to see what it does. I've got 20' right in the fire, but like I said, I'm going to change it next summer to an open system to be safer, thanks to the warnings on this forum. Last winter I did for the first time have the temp/pressure relief valve spit a little when it got too hot, so I would run some hot water down the drain to cool it off. This winter I'm watching it closer to make sure the water tank doesn't get that hot. I've got to check out this 'flashing to steam' talked about here. I'm pretty sure that is what is causing the snapping and popping I hear when getting the stove too hot too fast, but it never hurt anything, so I would welcome anyone explaining it better.

I have never made a diagram here. I'll have to have someone show me how. But my system is simple. The 20' of 1/2" copper tubing in the fire in the stove and then piped up stairs to the electric hot water heater, which never comes on in the winter, and returns from the water heater to the other end of the tubing at the stove, one line to the top and and one to the bottom of the water heater. At my hangar I've got an open system. I think 50' of 1/2" OD copper tubing in the fire of the stove circulating to a 30 gal. tank sitting on the stove, the top cut off of the water tank. Then 60' of tubing coiled in the hot water and circulating through the slab floor. I use pumps here for faster water flow. A couple times we've had the whole tank boiling away and splashing overboard. Usually the water in that tank is about 140 f while the heat is being sent to the floor. So I'm pretty happy with that setup.

But I'm a little jealous of your stove, which is like what i've got in mind to make next using firebrick. I like the long burns you're getting and it sounds like it is burning pretty clean and using the heat for the house instead of the great outdoors like most stoves. I'd love to cut my wood use in half too. Or better than that? Haha.

Phil Holbrook wrote:

But I'm a little jealous of your stove, which is like what i've got in mind to make next using firebrick. I like the long burns you're getting and it sounds like it is burning pretty clean and using the heat for the house instead of the great outdoors like most stoves. I'd love to cut my wood use in half too. Or better than that? Haha.

you are more than welcome to use my ideas and ask me questions. if you need diagrams, pics let me know.
I do plan to change my heat riser to instead of mainly refractory to more insulative to get faster start ups and hotter temps. its takes a bit to warm up to temps but then that may be the reason i get the effects i i get. so i think i am going to use both refractory cement and insulative brick to get the best of both results. i get a unique action with my RMH in that a full feed takes a moment to get chugging at full dragon speed and it burns off the wood gasses getting very hot as it turns the wood to charcoal and then as the charcoal collapses the system slows down to a slower less heat efficient burn as the charcoal glows with a small flame on it makes it burn like a charcoal grill as the coals sink to the bottom and bury into the ashes and then i use those ember to start the next fire... it was not planned exactly that way but the effect is extremely desirable to me.



* Phil Holbrook how hot do you think your stove gets that with the 20' of copper tubing in it?

my system:
1 large wood feeding capacity and wood logs size max 10'' wide 18'' in length.
2 long unattended burning times. the longest burn time with embers left was 8 hours. i can pack it up and go out and work come back and restart fire with out using a lighter.
3 left over embers make easy restarts.
4 multitasking system heats house, cook, bake and heats water.
5 My RMH is on wheels and is movable

I'm happy to hear that adjusting your chimney tee solved your condensation problem.

I would not jacket any of your exterior chimney in concrete, as that is not a good insulator and would cool down the chimney for a long time until it got warmed up, and even then in cold weather would be sucking heat out of the chimney, if not as fast as bare metal does.

Glenn Herbert wrote:I'm happy to hear that adjusting your chimney tee solved your condensation problem.

I would not jacket any of your exterior chimney in concrete, as that is not a good insulator and would cool down the chimney for a long time until it got warmed up, and even then in cold weather would be sucking heat out of the chimney, if not as fast as bare metal does.

thank you for the advice. today i have been putting fiberglass insulation around the 6'' smoke stack and then slipping 8'' duct around that instead. i have leaned away from using concrete around the smoke stack.

for the sanity of my wife i have decided to install a 6'' deep hood on the ceiling above the RMH with a 4'' exhaust pipe going outside to vent any smoke that may escape the RMH when opening the lid. i will take pics of it when complete.

Sometimes non-technical people demand changes to systems to satisfy their fears or tastes. It is often wisest to comply when the change will not have a serious negative impact on the system

Glenn Herbert wrote:Sometimes non-technical people demand changes to systems to satisfy their fears or tastes. It is often wisest to comply when the change will not have a serious negative impact on the system

you are correct i "fear" my wife's "tastes" and its "wisest" to "comply" or it will have a "serious negative impact"

as for the heat riser change. its an improvement on an already amazing system. cant go wrong with more insulation.

I bought QUIKRETE Portland 47-lb Gray Type-I/II Cement Mix to use for my bench coating. How do I mix it, what ratio did you use for your coating please

*** UPDATE *** I have completed the heat riser upgrade and here is a step by step pic set.

started building heat riser with refractory bricks in upright position around 6'' pipe in a hexagon shape instead of square. pointed the bricks with refractory cement and fireclay.
then i wrapped the heat riser with chicken wire for strength.


then i made a concrete slurry with refractory cement only and thoroughly soaked a small T-shirt in the slurry.


wrapping the concrete tshirt around chicken wire and heat riser.


completely wrapped


after putting together a 10'' duct and 4'' duct i slipped it over the heat riser then dumped loose perlite into the space between heat riser and duct.


all spaces completely full of perlite.


then i finished the top with a perlite refractory cement and fireclay mix and rounded it off.


*** concept idea proof of concept with my concrete slurry soaked fabric to strengthen heat risers and to create custom RMH inner cores by using your favorite high temp fabric such as fiberglass or rockwool or some other high temp fabric or flexible material and soaking it in a refractory cement slurry and doing a kind of "paper machete" around your choice of duct size for any shape of inner RMH core with multiple layers of slurry coated high temp fabric or flexible material. it would be possible to do multiple layers of ducting with perlite or insulating material in between each slurry covered duct.
think of the possibilities? let me know your thoughts.

i only wish i had thought of this idea before i built my RMH or i would have built the whole unit this way.

Bacon Lee wrote:
I bought QUIKRETE Portland 47-lb Gray Type-I/II Cement Mix to use for my bench coating. How do I mix it, what ratio did you use for your coating please

it depends on how "smooth" to the touch you want it. you need a little aggregate in it so test it with a little sand at a time to adjust to your taste. i used a 1 part sand 2 parts portland for a very smooth top and 2/2 for the sides.

it has been too warm to burn so i will update as i have new info. i am thinking about busting up the last mass bench and pulling out the water tank and hooking it up closer to phils idea in alaska almost like the water heater pic i posted.

UPDATE... i couldnt wait any longer. im addicted to my new RMH i had to do more testing with the new heat riser and its at least 10x better. im talking 0 (ZERO) to Dragon in 30 seconds! if not faster. my tiny starter sticks started growling immediately and i had no wait time and that is on a cold system. I do have to give credit to Glenn for suggesting to insulate the outside stack plus the new heat riser and it growls as soon as the lighter hits the wood shavings. ive never seen it roar liek this except at full heat after an hour of burn time and completely warmed up. this is amazing! i am recording burn times right now and i am almost 2 hours into a 1/2 feed chamber of wood. results so far are off the chart i am hoping not to melt the barrel top now.

Thanks for the link to your stove. I admire the fact that you have your own ideas. The water heating is a good idea and you could definately make that work, in more than one way. The thermal siphon that Phil H mentioned seems like a good idea, and perhaps a copper coil could even be mounted at the hotter end of the exhaust? Anyway I think water for a mass is a great idea. Kill 2 birds with one stone, so to speak. Every custom unit will require testing and tweaking, so its no big deal. You will get the kinks out in no time.

How does the 10" metal duct work around the riser? I plan on the same idea. And mine also has a 6" riser

John McDoodle wrote:Thanks for the link to your stove. I admire the fact that you have your own ideas. The water heating is a good idea and you could definately make that work, in more than one way. The thermal siphon that Phil H mentioned seems like a good idea, and perhaps a copper coil could even be mounted at the hotter end of the exhaust? Anyway I think water for a mass is a great idea. Kill 2 birds with one stone, so to speak. Every custom unit will require testing and tweaking, so its no big deal. You will get the kinks out in no time.

How does the 10" metal duct work around the riser? I plan on the same idea. And mine also has a 6" riser

youre welcome for the link. i have been studying RMH for almost 5 years now and my RMH design has seen many stages including up to the day i built it and added an access port and then the last upgrade of the heat riser. i wasnt joking about the internal temp my friend it literally turned my recommended REAL refractory cement perlite mix to dust. although i do think i used too much perlite. ($26 for 1 gal refractory cement) yes its expensive so if your buying a $12 50lb bag of so called refractory cement with fibers in it, its not refractory.

the water tank does store a bunch of the heat and may drawn a bit more than i like but im not complaining about the draw i got because its no less than awesome.
i have studied RMH like a said for a while and my orignal system was all steel on paper but then after much research quickly changed to refractory cement and now its been upgraded to a refractory/perlite/fireclay/fire brick system for a complete high temp, high insulative system on wheels that does it all with looooong unattended burns and fast start ups.

getting the book, watching videos and reading this forum over and over in the shadows so to speak with out an account until i actually built my first RMH a few weeks ago gave me the ability to build a "correct" RMH the first time. given the riser i had would have lasted me a season or two i wanted something more long term with more insulation, hence the upgrade. but i couldnt have done it without the fine folks here or without the book and videos.


my old riser had a 10'' duct around it. my new upgrade has an expanded 10'' and a 4'' duct adding 4'' to the outer duct circumference. since i used fire bricks i dont have to worry about the contents of the perlite insulation spilling inside from a broken down heat riser build so the outer air space got filled with loose perlite only for greater insulation.

What do you call refractory cement? I want to know so I can buy. Would you please take a picture of the bag and upload so I can see

Bacon Lee wrote:What do you call refractory cement? I want to know so I can buy. Would you please take a picture of the bag and upload so I can see

this is the exact product i have been using. good for over 2000+ degrees F
im not sure where you would get it. internet is expensive to ship this i got it for $26 for 1 gal or 10lbs at my local brick/cement store.
heat stop

i dont know about all of you, but once you get your first correct running RMH built and started, tinkering with it is addicting. hot rodding your box to make it perform better than it did and watching it work is a sight to be seen. i always have things going through my mind trying to think of how i can increase what it does. whether its heating water, cooking, baking or heating your house more efficient im always drawing things out.