Double Garage RMH Questions for Ernie and Erica

Hi there

I am new to the rocket mass heaters and have done hours of research, however I don't want to spend much money making one, I want to heat a double garage using a "portable" RMH basically contained in an oil drum.

Will a heater with 4inch aluminium tubing get Hot enough to melt the alloy?

How much heat will a system like this produce? With no cob just an exhaust running along a floor for about 3m to the outside of the building?

Is there an equation to work out the heat produced by different size systems.

And has anyone ever made a self contained system like this and if so do you have plans for it please?

I'm sorry about all of the questions but I am planning on building it this weekend or next and just didn't want to waste my money.

Kind regards
Josh

Hi Josh, I would like to piggyback onto your questions if I can because your system sounds extremely similar to the one I want to build in my shop. I have Evan's and Jackson's book, I have listened to ALL of the podcasts ernestly, and I have read through most of the posts here that I thought might be relevant to my questions.

I want to build a heater inside the bottom 1/3 of a 55gal drum. I DON'T want to run it through a thermal mass right now.

I have some insulated pipe I want to use for the heat riser; it came out of my attic when we replaced pipe in our house years ago. I believe it is 8". That seems big to me. Is it?
And, is it insulated enough as it is, or does it require more?

And, I am planning on using a 35gal drum for the heat exchanger. Is that too small for that 8" pipe?

I have done a test run with the brick stove built inside the 1/3 drum and it fired great.
I know my questions are somewhat elementary, but that's where I am right now.

Thanks all.

Four incher working not too bad for me. Don't use aluminium tube. If you can, make your heat riser tube thicker than mine, it's only stove pipe. Use at lesat 5mm thick steel.

https://permies.com/t/10367/stoves/Cyclone-rocket

Ok, somehow I missed your post on the cyclone. That is sort of what I am attempting just not so big.

Alright this gives me ideas. I'm doing mostly brick on the inside of mine 'cause that's what I got.

Brett, carefull with the not soo large. There's a point where you can't scale down anymore. Best advice i can give. Use a J tube a bit bigger, like 6 incher. And make your stove as tall and narow as you can to increase heat exchange surface. If you plan to heat the place without mass.

Joshua Bannister wrote:Hi there

I am new to the rocket mass heaters and have done hours of research, however I don't want to spend much money making one, I want to heat a double garage using a "portable" RMH basically contained in an oil drum.

<snip>

.......... I am planning on building it this weekend or next and just didn't want to waste my money.

Kind regards
Josh

Ernie and Erica seem to be away at the moment, but if you are new to this I think the advice would be build one outside first and get some experience. I've done weeks of research but building them is a whole different game.

brett watson wrote:Hi Josh, I would like to piggyback onto your questions if I can because your system sounds extremely similar to the one I want to build in my shop. I have Evan's and Jackson's book, I have listened to ALL of the podcasts ernestly, and I have read through most of the posts here that I thought might be relevant to my questions.

I want to build a heater inside the bottom 1/3 of a 55gal drum. I DON'T want to run it through a thermal mass right now.

I have some insulated pipe I want to use for the heat riser; it came out of my attic when we replaced pipe in our house years ago. I believe it is 8". That seems big to me. Is it?
And, is it insulated enough as it is, or does it require more?

And, I am planning on using a 35gal drum for the heat exchanger. Is that too small for that 8" pipe?

I have done a test run with the brick stove built inside the 1/3 drum and it fired great.
I know my questions are somewhat elementary, but that's where I am right now.

Thanks all.

Without thermal mass you need to have a major amount of heat exchange to air to get what you so efficiently burned in the rocket. Mass is a key part of using these for heating but people frequently don't understand that until they live with it. Hot air is fleeting but if that is what you want, I do recommend sizing down the 8" riser to 6" (or smaller) and playing with your heat exchanger (you need much more than a 35 gal drum) until your exit flue temp is down around 180 F to avoid condensation but get all you can. This is tricky and can be dangerous because all of your fittings etc. need to be gas tight to avoid CO leakage. TEst Test TEST outside first!

Bret thats fine i think you are looking at the same one as me, Satamex that is not the one i mean, i was looking at one that was like the normal heaters but the exhaust just didn't go through a thermal mass. i made a tiny tiny version to try and see if it works (FYI a tiny version does not work although i can get suction there is not enough room for the burn) here is the link to my post about it (same post as this but with the mini one on)

https://permies.com/t/13203/stoves/Questions-Rocket-Mass-Heater-self

https://permies.com/t/13203/stoves/Questions-Rocket-Mass-Heater-self

There are several problems with trying to scale combustion devices, just as there are with scaling other things where physics is involved. The biggest single effect is the pipe diameter. Gas flow is dependent on the 4th power of the diameter. i.e. 1/2 the diameter gives 1/16th of the gas flow at a given pressure. with care you could make a 3" pipe and a container like a bucket work ok, but it would be very different from a 6" set up.

For the small one try making the pipes around 2/3rd of the tin diameter, and make the burn tunnel short. I would use something other than copper, it might melt.

Ahhh well that makes sense then thanks just out of information do you know what sort of temps you get out of a 6" system? and how do you work out the height of the burn tube?

It's worth going through most of the posts on the first two index pages. I can't remember which ones they are but temperatures and tube heights ae discussed several times. They are interdependent, so lowering the burn tube increases output from the barrel, but it also moves the hot spot around in the barrel and reduces the heat into the mass store. The reason I'm not putting details in is I don't know enough about it.