Rocket Mass Heater pipe

Hello,

I have a couple of questions about the rocket mass heater. Would you recommend using stainless steel stove pipe for the heat riser and is it okay to use gas vent duct for the rest of it? My concern is the gas vent duct in the bench seat may not be able to handle that high of a temperature and is not designed for fire and it made deteriorate? What do you folks think?  Also is it okay to use a 6 inch system with a 6in heat Riser and a 10in insulated pipe around it in combination with a 55 gallon drum? Or is it better to use the 6-inch pipe with a 10 inch pipe heat riser with a 30 gallon drum? Also how many inches should the heat Riser be away from the top of the 55 gallon drum? Is 2 inches okay or three? I really like Paul Wheaton's rocket mass heater with pea gravel and wood box. That's the concept I'm going to go with because it seems so easy and effective. A lot easier than mixing mud and cobb. Thank you very much for your response and information, I appreciate it.

Brian

Hi Brian, sounds like you and I are in the same boat except I may have read a lot more in these forums. I've not built my heater yet but I'll share what I think I've learned. The suggested height from the top of the core to the barrel is 1 1/2". The metal in the burn chamber isn't necessary other than to give you something to form the core. The smooth surface of the metal will actually reduce the necessary turbulence needed for clean combustion. I plan to make my core with a perlite mix using paper concrete forms (anyone's input on that idea would be appreciated). It will be a 2" thick cylinder with no inner or outer skin. Unless you're heating a huge space a 6" riser should be plenty. I'm planning to build my "test" rocket heater next week and afterward buy one of the books or CDs offered in this forum to iron out the kinks before building the whole RMH. I hope this helps and if I gave you any bad info hopefully someone on here will yell at me.

Brian Bennett wrote: Hello,

I have a couple of questions about the rocket mass heater. Would you recommend using stainless steel stove pipe for the heat riser and is it okay to use gas vent duct for the rest of it? My concern is the gas vent duct in the bench seat may not be able to handle that high of a temperature and is not designed for fire and it made deteriorate? What do you folks think?  Also is it okay to use a 6 inch system with a 6in heat Riser and a 10in insulated pipe around it in combination with a 55 gallon drum? Or is it better to use the 6-inch pipe with a 10 inch pipe heat riser with a 30 gallon drum? Also how many inches should the heat Riser be away from the top of the 55 gallon drum? Is 2 inches okay or three? I really like Paul Wheaton's rocket mass heater with pea gravel and wood box. That's the concept I'm going to go with because it seems so easy and effective. A lot easier than mixing mud and cobb. Thank you very much for your response and information, I appreciate it.

Brian

I guess I should go with an 8-inch system because I'm going to be heating a 2000 square foot house. I was thinking about building my core  with a 50/50 mix of concrete / pearlite . What do you think? 4 in thick. With an 8-inch system do you think the core inner Dimension burn chamber should be around 7 inches? I hope nobody gets me wrong, I wouldn't mind doing cobb, I would probably prefer it but I'm so darn busy I just don't have the time. I don't like investing a lot of time into things as much as I used to because everything I worked hard for all my life was taken by my former ex-wife b**** from hell.  I hope you understand. Thank you.

my first heat riser was a 6 inch double wall stainless pipe, I knew I shouldn't do it, but the clay perlite had not hardened properly and I was getting cold. two months into the winter we hit a warm spell, I took the barrel off and removed the stainless pipe which looked great from the outside--until I set it down and heard a clunk as the inside stainless lining of the pipe fell loose and hit the ground.  The temps in a good heat riser are too intense for metal. The easiest and probably best I have seen is using a ceramic fiber blanket, good to 2300 F  line an 8 inch stove pipe with a 1 inch blanket and you have a 6 inch riser--almost too easy. 1 inch of ceramic blanket equals 3+ inches of perlite+ clay

The old fashioned way is to cast perlite and clay, or sawdust and clay  or refractory cement and perlite, refractory cement and clay and perlite--imagination is wonderful and can adapt just about any available material to any application, but any metal will burn out on the inside of the heat riser, but even thin metal may last forever on the outside because of the insulation and the lower (relatively) temps.

also, note that the amount of space between top of riser and barrel-- 1&1/2 may be the minimum, but having more space is a plus. It lessens the temperature on the barrel top and spreads out the heat more evenly

Please take a little more time now and read up on batch burners and bells, you may find they serve your needs better---- here is an example, but there are lots more designs--note this is a 4 inch riser with a pretty big firebox and a small footprint and a large mass

in the video Donkey talks about necessity being the reason for the barrels and mud but the possibility to do other styles and keep the efficiency of the RMH is still there for numerous other adaptations.

Please read as much as you can, set up a test outside (i used a pile of sand), watch the flame burn sideways, use a stainless pipe riser for the test as a proof of concept, then read some more

then read it all over again.

I find that the information dense material I may have to read three or four times and do research in between just to be able to really understand what is happening
have fun

Brian Bennett wrote:

Brian Bennett wrote: Hello,

I have a couple of questions about the rocket mass heater. Would you recommend using stainless steel stove pipe for the heat riser and is it okay to use gas vent duct for the rest of it? My concern is the gas vent duct in the bench seat may not be able to handle that high of a temperature and is not designed for fire and it made deteriorate? What do you folks think?  Also is it okay to use a 6 inch system with a 6in heat Riser and a 10in insulated pipe around it in combination with a 55 gallon drum? Or is it better to use the 6-inch pipe with a 10 inch pipe heat riser with a 30 gallon drum? Also how many inches should the heat Riser be away from the top of the 55 gallon drum? Is 2 inches okay or three? I really like Paul Wheaton's rocket mass heater with pea gravel and wood box. That's the concept I'm going to go with because it seems so easy and effective. A lot easier than mixing mud and cobb. Thank you very much for your response and information, I appreciate it.

Brian

I guess I should go with an 8-inch system because I'm going to be heating a 2000 square foot house. I was thinking about building my core  with a 50/50 mix of concrete / pearlite . What do you think? 4 in thick. With an 8-inch system do you think the core inner Dimension burn chamber should be around 7 inches? I hope nobody gets me wrong, I wouldn't mind doing cobb, I would probably prefer it but I'm so darn busy I just don't have the time. I don't like investing a lot of time into things as much as I used to because everything I worked hard for all my life was taken by my former ex-wife b**** from hell.  I hope you understand. Thank you.

For 2000sqft house. You'd better start to look at batch rockets

http://batchrocket.eu/en/

For the core. Don't use concrete. Only castable refractory, "ciment fondu" or fireclay.

And no metal to the parts exposed to fire.

https://permies.com/t/52544/metal-burn-tunnel-heat-riser

thank you very much for your information, I wish each one of these  comments had a reply button  because I'm not sure how to reply  should I be writing in my own space or this one? Anyways based on what you said and based on  other things I have seen and read   tell me what you think of this idea: I will make the core out of plywood that will burn out from the inside. After the plywood core burns out from the inside the inside dimensions will be approximately 5 1/2 to 6 in  in the burn chamber.  I will cast The Core with refractory cement and perlite. The burn chamber will be 4 inch thick walls. How much of each is a question? 50/50? Then I will use a 6 inch single wall pipe with a 10 inch single wall pipe around it and in the middle of the heat Riser I will use refractory cement and perlite so even if the center pipe deteriorates and burns out it will still hold its form because of the refractory cement.  my second question was should I use a 30 gallon drum or a 55 gallon drum around that?  then I will build the bench seat out of thick wood frame and fill it with pea gravel after I run the 6 inch single wall duct through it, the duct will exit behind the barrel and then through the wall. It will rise approximately 6 feet up and then have a 90-degree elbow and go two feet out  then I might go up another 2 feet  and then put the cap.
I'm going to put 1 and 1/2 or 2" thick red flagstone on top of the bench seat.  the bench seat will be approximately 12 ft long.

tell me what you think, and
1)  what is the mix of perlite and refractory cement?
2)  30 gallon drum or 55 gallon drum?

Thank you for your input, I appreciate it


quote=bob day]my first heat riser was a 6 inch double wall stainless pipe, I knew I shouldn't do it, but the clay perlite had not hardened properly and I was getting cold. two months into the winter we hit a warm spell, I took the barrel off and removed the stainless pipe which looked great from the outside--until I set it down and heard a clunk as the inside stainless lining of the pipe fell loose and hit the ground.  The temps in a good heat riser are too intense for metal. The easiest and probably best I have seen is using a ceramic fiber blanket, good to 2300 F  line an 8 inch stove pipe with a 1 inch blanket and you have a 6 inch riser--almost too easy. 1 inch of ceramic blanket equals 3+ inches of perlite+ clay

The old fashioned way is to cast perlite and clay, or sawdust and clay  or refractory cement and perlite, refractory cement and clay and perlite--imagination is wonderful and can adapt just about any available material to any application, but any metal will burn out on the inside of the heat riser, but even thin metal may last forever on the outside because of the insulation and the lower (relatively) temps.

also, note that the amount of space between top of riser and barrel-- 1&1/2 may be the minimum, but having more space is a plus. It lessens the temperature on the barrel top and spreads out the heat more evenly

Please take a little more time now and read up on batch burners and bells, you may find they serve your needs better---- here is an example, but there are lots more designs--note this is a 4 inch riser with a pretty big firebox and a small footprint and a large mass

in the video Donkey talks about necessity being the reason for the barrels and mud but the possibility to do other styles and keep the efficiency of the RMH is still there for numerous other adaptations.

Please read as much as you can, set up a test outside (i used a pile of sand), watch the flame burn sideways, use a stainless pipe riser for the test as a proof of concept, then read some more

then read it all over again.

I find that the information dense material I may have to read three or four times and do research in between just to be able to really understand what is happening
have fun

For a 2000 square foot house, an 8" system is a minimum. 6" is unlikely to keep you warm. It does matter what your climate is like, as well as how well your house is insulated.

I would use a metal duct for the outer wrapper of the riser, for ease of handling in the future.

I would also recommend you read the batch box links, as that will probably serve you better than a J-tube for a large house.

A pebble bed mass is reported to be less efficient than a solid mass; its sole advantage is that it can quickly be removed and modified. 12' of duct in a bench will not allow a lot of the heat to be absorbed by the mass. It would have to double back twice at least.

Are you going above the roof with your chimney? It is critical to do that in most circumstances, to avoid risk of smokeback.

If you end up doing a batch system--which I also recommend, do not leave the metal inside the core. I did that with one of my rockets figuring the same thing you did and what happens is the metal did  not uniformly evaporate, rather it fell in chunks, clogging up everything so there was lots of smoke coming back. A batch burner has a more narrow port opening into the riser and those chunks might not come out so easy. As I remember it, even with the wider opening of the rocket into the riser I had to struggle a bit to get them out without having to take the whole thing apart.

Perlite clay, or perlite refractory is losing favor and I strongly encourage you to look into ceramic fiber, it is much more effective than perlite, and there is even some question as to whether it (perlite)might melt out of the system eventually requiring a rebuild.

To date there is evidence that it does melt, but whether that is a total self destruct or not I'm not sure, it can be used around the firebox, but even there ceramic fiber just performs better.

This is a site I wished someone had turned me toward very early on, you can watch the development of the batch burner step by step, investigate findings about different core materials and their experiments, and generally save yourself a lot of time building something that has already been built and discarded.

Rocket stoves are great, but they have their drawbacks, I just did a jury rig adaptation to my stove to accept a batch attachment instead of the J tube, and I think my next step is to dismantle my benches and all the ductwork and substitute a bell and batch burner in a totally new and better design.

It may seem  like this is just more stuff you don't need and you're' tired of reading and want to get busy, but trust me, heating a 2000 sq ft home with tiny sticks and frequent attention to the fire is going to get real old real fast. It can be done with a rmh---if you have nothing else to do

Brian Bennett wrote: Hello,

I have a couple of questions about the rocket mass heater. Would you recommend using stainless steel stove pipe for the heat riser and is it okay to use gas vent duct for the rest of it? My concern is the gas vent duct in the bench seat may not be able to handle that high of a temperature and is not designed for fire and it made deteriorate? What do you folks think?  Also is it okay to use a 6 inch system with a 6in heat Riser and a 10in insulated pipe around it in combination with a 55 gallon drum? Or is it better to use the 6-inch pipe with a 10 inch pipe heat riser with a 30 gallon drum? Also how many inches should the heat Riser be away from the top of the 55 gallon drum? Is 2 inches okay or three? I really like Paul Wheaton's rocket mass heater with pea gravel and wood box. That's the concept I'm going to go with because it seems so easy and effective. A lot easier than mixing mud and cobb. Thank you very much for your response and information, I appreciate it.

Brian

I forgot to mention that I live just north of Santa Fe New Mexico and it doesn't get that super cold and my house is well-insulated

Brian Bennett wrote:

Brian Bennett wrote: Hello,

I have a couple of questions about the rocket mass heater. Would you recommend using stainless steel stove pipe for the heat riser and is it okay to use gas vent duct for the rest of it? My concern is the gas vent duct in the bench seat may not be able to handle that high of a temperature and is not designed for fire and it made deteriorate? What do you folks think?  Also is it okay to use a 6 inch system with a 6in heat Riser and a 10in insulated pipe around it in combination with a 55 gallon drum? Or is it better to use the 6-inch pipe with a 10 inch pipe heat riser with a 30 gallon drum? Also how many inches should the heat Riser be away from the top of the 55 gallon drum? Is 2 inches okay or three? I really like Paul Wheaton's rocket mass heater with pea gravel and wood box. That's the concept I'm going to go with because it seems so easy and effective. A lot easier than mixing mud and cobb. Thank you very much for your response and information, I appreciate it.

Brian

I forgot to mention that I live just north of Santa Fe New Mexico and it doesn't get that super cold and my house is well-insulated

The average night time winter temperature is around 20 degrees.

I would really really REALLY recommend you purchase the Rocket Mass Heater Builders Guide: https://www.amazon.com/Rocket-Heater-Builders-Guide-Step-ebook/dp/B01FIKD1Y8

It has all the info you should know for building efficiently and safely. Things like, how close to your combustible walls will it be, what kind of floor/foundation will its 2-3 tons of weight be on, how long can the heat exchange be based on size and number of turns, sizing of everything, etc.

There are lots of variations out there, many still in testing, but the book gives you a rock-solid, known to work system and you should be building that for your first one that you will rely on for heating. Answers we give you are based on the limited info we have about your site/setup, and if some variable changes or we didn't know, we could give you less than optimal answers.

bob day wrote:If you end up doing a batch system--which I also recommend, do not leave the metal inside the core. I did that with one of my rockets figuring the same thing you did and what happens is the metal did  not uniformly evaporate, rather it fell in chunks, clogging up everything so there was lots of smoke coming back. A batch burner has a more narrow port opening into the riser and those chunks might not come out so easy. As I remember it, even with the wider opening of the rocket into the riser I had to struggle a bit to get them out without having to take the whole thing apart.

Perlite clay, or perlite refractory is losing favor and I strongly encourage you to look into ceramic fiber, it is much more effective than perlite, and there is even some question as to whether it (perlite)might melt out of the system eventually requiring a rebuild.

To date there is evidence that it does melt, but whether that is a total self destruct or not I'm not sure, it can be used around the firebox, but even there ceramic fiber just performs better.

This is a site I wished someone had turned me toward very early on, you can watch the development of the batch burner step by step, investigate findings about different core materials and their experiments, and generally save yourself a lot of time building something that has already been built and discarded.

Rocket stoves are great, but they have their drawbacks, I just did a jury rig adaptation to my stove to accept a batch attachment instead of the J tube, and I think my next step is to dismantle my benches and all the ductwork and substitute a bell and batch burner in a totally new and better design.

It may seem  like this is just more stuff you don't need and you're' tired of reading and want to get busy, but trust me, heating a 2000 sq ft home with tiny sticks and frequent attention to the fire is going to get real old real fast. It can be done with a rmh---if you have nothing else to do

I agree with you my friend, I better carefully consider all the options before starting the build, I kind of like the idea of the rocket mass heater with the bench seat and duct system because when I did have a lot of small stuff on my property that I wanted to clean up but I guess I can just throw it in the batch box heater also, if there's any way you can let me know what your design would look like by sending me any pictures I'd be happy to give you my email address or phone number so you can either text or email them to me because I like your idea. It's better to throw a larger wood and have a slower burn so you don't have to mess with it as much during the couple hours of burning. I'll have to look up Bell and batch box burner on YouTube or the internet to see if I can find anything. Thank you for your information, I appreciate it. It's better to know more and build it once rather than take it apart later on.