Tiny House RMH

I was reading the thread about tiny homes and psychology over HERE:  https://permies.com/t/40/44704/Psychology-Tiny-Houses  and I noticed the wood stove.  It got me wondering if/how one would work a RMH into such a tiny space.  I am no RMH expert, but the ones I have seen rely on a long cob or masonry bench to soak up heat and slowly release it over time.  It seems like a Tiny Home would be challenged for such a bench.  Is there some other option that I am simply overlooking?  Forgive me if this question has been asked before, it just seems like a great match if it can work:  a very efficient heater in a tiny volume of home.

Eric

Hi Eric;
You could create a small batch box and a small brick bell.
Bells can be tall and skinny or low and flat.
As long as the ISA (internal surface area) for the size batch you are using is not exceeded, they can be any shape that fits.
Batch boxes can be built down to 4" but they do require almost constant tending.

Thanks Thomas,

That makes a lot of sense.  So it can be done, but not the thing that can be set to burn and just leave for hours.  Interesting though.

Eric

After you spent some time getting your bell up to temp, like any mass heater you can walk away for quite a while.
Most of these tiny homes are well insulated I think for the right person/people a tiny batch for a tiny home is a great idea!

I want to build a RMH in my 12x20 one-room bunk house. My question is about weight load. Can a 2x6 wood framed floor support a RMH?

Nick Neufeld wrote:I want to build a RMH in my 12x20 one-room bunk house. My question is about weight load. Can a 2x6 wood framed floor support a RMH?

I'm thinking about a 6" J tube. I figure with a "5 minute riser" and a pea gravel bench that might have less mass than optimal, then I can keep the weight down.

If anyone has cautionary tales of collapsed floors please share.

The load  capacity of a 2x6 joist floor depends on how the mass is placed and distributed on the floor. If near an end and spread out over several joists, it may be fine. If in the middle of a span and concentrated on a few joists it would need to be reinforced with one or more pillars from below.

Nick, are those 2x6's fully suspended across the width of the room?  Do you know the spacing?  I have never had joists of anything less that 2x10.  I know that 2x8 can be used with more narrow spacing and I guess 2x6 with more narrow spacing still.  Can you access the joists from underneath to reinforce?  I know this is a lot of questions.  

I would think that the RMH being close to a wall would minimize the load on the center of a 2x6, but I honestly don't know.  Perhaps there is some load chart we can find?

Eric

Thanks for the replies. The floor joists are only in 6 foot spans. They span the 12 foot length of the building and are supported by timbers underneath at both ends and the middle. The joist spacing is 16".

Nick Neufeld wrote:I want to build a RMH in my 12x20 one-room bunk house. My question is about weight load. Can a 2x6 wood framed floor support a RMH?

Maybe knowing the design you want to use might help folks answer your question.

Are you going to buy something or build it from scratch?

Will it be anything like either of these?




From here

Or something like this:


from here

Hi Nick;
I think your floor will be plenty strong enough.  6' 2x6 on 16" centers.
Your RMH will be sitting next to a wall with timber support underneath crossing multiple joists.
I would build on it.
So a 6" J tube and you are thinking of a pebble mass.  
I suggest you forget the pebble mass and build a bell instead.  
Bells work great and they weigh less than a solid mass and have no horizontal pipes to plug up.
Pebble mass does work but is not efficient at holding heat for a long time, it is a tiny mass with zillions of insulating air pockets.
I also suggest you consider building an 8" J rather than a 6"
A 6" feed tube is small and only burns for 30 minutes or so and crooked wood can easily jam up.
An 8" feed tube is much more user-friendly and burns 45 minutes to an hour without attention.


 

I presume your 2x6s are 12' long supported by a beam in the middle, giving 6' clear spans. This is significantly stronger than two 6' joists meeting in the middle, and as long as the beam is strong enough, it will do fine for a small RMH. At worst, I would add another support for the beam under the RMH location. I second the advice to use a bell for your mass. It can be any shape you like as long as internal surface area guidelines are followed. I would guess for your small structure you would get more of a seat than a bed-sized bench if you go that way, though an 8" J-tube would call for a larger surface area.

Thanks for the replies all!
I'm going to go for it. I have a lot more learning to do on RMHs before I start. Will start with Paul's video package and probably track down a copy of Ernie and Erica's builders guide.

Some links for the book:

https://permies.com/wiki/57365/Rocket-Mass-Heater-Builder-Guide

https://permies.com/t/40993/Ernie-Erica-Wisner-Rocket-Mass