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rocket mass heaters

Do I need to rebuild the burn unit or not?

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posted 4 years ago

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Hello everyone,
I have the base and the initial burn chamber and heat riser openings built for the 8" system. You can see in the 2 pix I attached that my heat riser opening is almost 8" wide by 7 and 7/16"= 59.5". I'm not sure how this happened but I am sure it was my fault, hahaha. Also, the other picture shows my interior length to be 24.75". Does this mean I have to take this unit apart and build it again to get the exact 7 X 7.5" or 54"measurements? My burn chamber dimensions are also slightly off at 7 3/8" x 7 3/8" = 54.39". Thanks for any help you can offer!

-Ryder

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thomas rubino

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posted 4 years ago

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Hi Ryder; Congratulations on becoming an apprentice Rocket Scientist! We will rush your lab coat out as soon as we have any...until then jeans and a shirt will do!
By accident even though your measurements are slightly small at the feed tube and slightly large on the riser , It will be fine.
Had you managed to do that the other way with a larger feed tube then we would have said it needs redone.
It is good to go as is! Keep building and now that we know you are building we would like plenty of photo's!

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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Daniel Ray

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posted 4 years ago

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Looks good to me. Your riser is slightly larger than the feed which is good. Just finish the riser to specs, keep the vertical run to the recommended length, give it a final vertical chimney to exit and it should run great. You may need to use a brick to limit the size of the burn chamber once you get it going. I always had to use one on mine to get a good draft. Post lots of photos!

Aaaah, beaten to the post again. I second Thomas' reply.

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Ryder Wooten

Posts: 15

posted 4 years ago

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Hahaha... Thomas seems to be the 1st responder on many post in the RMH. I noticed as I have read through the section. I appreciate the knowledge and the quick responses! Thanks Thomas!! I am glad to hear I messed up correctly and I will post more pix for sure. Thanks again for the inspiration to everyone in this forum/community.

Ryder Wooten

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posted 4 years ago

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Good morning,
I am getting ready to continue work on my RMH but as I was reading through the Wisner’s builders guide some questions came about. On page 98 it shows a picture of an exposed heater build without the cob etc. I noticed there is no tape on the stovepipe connections. So my question is should I not use tape to seal those connection areas? I have a high temperature tape that is supposed to withstand up to 2000F. I attached a picture from the book as well as of my current working areas. Thanks for any help offered!

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thomas rubino

rocket scientist

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posted 4 years ago

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Hi Ryder;
I used metal tape on all the joints especially where it comes out of the mass.
I used it in the mass because it seemed the right thing to do.
I suspect that buried under 2 foot of cob and rock it matters not!

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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Thanks Thomas! You’re the best!!

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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Hi Ryder;
I would like to make a suggestion before you get much farther along.
At the far end you have a 180 degree turn and a cleanout tee.
I propose that you remove the 180 and the cleanout!!! Surprised???
It has been found that if you build a brick box at that spot.
Run your horizontal pipe in and another out.
Place the cleanout tee so you can access both horizontal pipes to remove ash once a season.

Doing this eliminates a big restriction in your piping and gives a nice ash collection point.

You will not find this in the builders guide. It was innovated after printing.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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A few more things. You will want insulated cob under those pipes.
And you could use much cheaper and longer sections of HVAC pipe when inside the mass.
One piece of the black pipe where it starts into the mass and another when it pops up out of the mass.
The rest can be 5' long thin wall hvac pipe.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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thomas rubino wrote:Hi Ryder;
I would like to make a suggestion before you get much farther along.
At the far end you have a 180 degree turn and a cleanout tee.
I propose that you remove the 180 and the cleanout!!! Surprised???
It has been found that if you build a brick box at that spot.
Run your horizontal pipe in and another out.
Place the cleanout tee so you can access both horizontal pipes to remove ash once a season.

Doing this eliminates a big restriction in your piping and gives a nice ash collection point.

You will not find this in the builders guide. It was innovated after printing.

I don’t understand what you are saying. So take out the 180 and the T and then do what? Thanks for your help!

Is there something online to look at?

Ryder Wooten

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posted 4 years ago

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I am getting ready to put the chimney through the greenhouse roof. I cut the hole in the roof but my question is after the 18” insulated pipe goes thru the roof do I have to use another piece of insulated pipe to finish the chimney or can I attach stovepipe to the insulated piece? Thanks

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thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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Hi Ryder;
No pictures so I'll try to explain from your picture.

Imagine removing the two 90 degree corner pipes and the cleanout tee.

What you have left are two straight pipes. If they are different length then make they both the same .

Put a (cob)wall across your mass so both pipes stick thru the (cob) wall.

On the very end of your mass create a cleanout port that faces the two pipes. (With a flashlight you should be able to look through the port and see down either straight pipe).

You will need a ceiling (roof) on your "box" cement board works well, used metal roofing would also work.

After your "box" has its roof than cover it with cob and rock like the rest of your mass.

Next your chimney question.
After you are thru your plastic roof the safety reason for insulated pipe is gone.
However it would be best if you finished with insulated pipe to the top.
A happy rocket stove has a warm exhaust stack. They draw much better.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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Oh ok I think I understand now. I understand what you’re saying about the chimney as well. I thought that was the case to have a warm stack but was tryin to not buy that expensive insulated pipe. I will buy another 18” insulated piece that will give me approximately 30” above the roof height. I know this isn’t high enough according to the 3’ height requirement above roofs. So do I have to buy the 36” insulated pipe or will the second 18” piece suffice? I definitely don’t want to buy the 36” piece because of cost but if it’s mandatory for regulatory compliance I probably should buy that piece. Thanks again for all your help Thomas!

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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One more 18" will be fine unless strong winds are common .

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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thomas rubino wrote:Hi Ryder;
No pictures so I'll try to explain from your picture.

Imagine removing the two 90 degree corner pipes and the cleanout tee.

What you have left are two straight pipes. If they are different length then make they both the same .

Put a (cob)wall across your mass so both pipes stick thru the (cob) wall.

On the very end of your mass create a cleanout port that faces the two pipes. (With a flashlight you should be able to look through the port and see down either straight pipe).

You will need a ceiling (roof) on your "box" cement board works well, used metal roofing would also work.

After your "box" has its roof than cover it with cob and rock like the rest of your mass.

Next your chimney question.
After you are thru your plastic roof the safety reason for insulated pipe is gone.
However it would be best if you finished with insulated pipe to the top.
A happy rocket stove has a warm exhaust stack. They draw much better.

Thomas,
As I am contemplating your new way with the box I’m wondering what should the size of the box be? So you want to build the box out of cement board on a wooden frame and nail the boards to the frame? Or can I build the cob wall then have the box area just be cinder blocks but put a cement board roof? Sorry for all the questions but you got me thinking! Thanks

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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Just a cinder block box with cement roof. It would be nice if you cobbed inside the box to make it smooth, and hold heat longer.
A low spot for ash to settle would be handy as well.

Then you would cover the roof with cob / rock to seal it up and hold more heat.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Gerry Parent

Rocket Scientist

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posted 4 years ago

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Photo showing an example of what Thomas was referring to built by Kirk Mobert

Also a video showing the dismantling of it rocket bell retrofit

Hutstove01.jpg

Silence is Golden
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Ryder Wooten

Posts: 15

posted 4 years ago

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Thanks Gerry! Thats a great illustration!

Ryder Wooten

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posted 4 years ago

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Is there still a chimney near the barrel?

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

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posted 4 years ago

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Hey Ryder; You can see the chimney pipe in Gerry's photo.
Right next to the barrel . Just above the outgoing pipe.
Its just not connected yet.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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Alright I’m back. This has been a long project just because I work so much. I have the heater functioning except for 1 issue. When I start the fire it smokes back out of the firebox. I can’t have that happen as it will damage my plants and the whole greenhouse fills up with smoke. I attached a few pix since it wont let me upload videos. The smoke also comes out of the chimney stack. From what I have read and watched online everything says the chimney should have no smoke and only steam will come out of the chimney. So what am I doing wrong? I am burning dried oak mostly. I know my mass is still wet so I am wondering if that has anything to do with the smoke issue. Thanks for any help. I truly hope this works as it is a must for my greenhouse to work properly. Thanks again everyone and I appreciate the community of helpful people!

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Phil Stevens

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posted 4 years ago

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Fear not, Ryder. The smoke and balkiness is exactly what we expect when firing a new RMH with cold, wet mass. As things dry out and warm up it should roar to life and behave like a proper dragon. Keep burning fires, using small and well-seasoned wood, and you should see the trend with every burn.

thomas rubino

rocket scientist

Posts: 6528

Location: latitude 47 N.W. montana zone 6A

3398

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posted 4 years ago

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Hi Ryder;
Never fear your heater will do the job. You need to dry all the moisture from your cob. This takes weeks or several months.

Remind me about your system. It is an 8" J , how much pipe do you have in your mass?
Did you use the piping as it was or did you put a small box at your 180?

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Ryder Wooten

Posts: 15

posted 4 years ago

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Phil Stevens wrote:Fear not, Ryder. The smoke and balkiness is exactly what we expect when firing a new RMH with cold, wet mass. As things dry out and warm up it should roar to life and behave like a proper dragon. Keep burning fires, using small and well-seasoned wood, and you should see the trend with every burn.

Thanks Phil!

Ryder Wooten

Posts: 15

posted 4 years ago

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Thanks Thomas! Yes an 8” J system with 22’ of pipe inside the mass. I sealed the pipe so I did not do the open chamber at the 180. I had already built the mass when you all brought my attention to this new technique. I will be using that open 180 technique on my next build though for sure. Thanks again for all your support and knowledge!

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