Pre-planning for a Rocket mass heater

Hello! I'm new to the forum and recently learned of the rocket mass heater concept.
I recently moved out to the woods, and was originally considering a conventional wood burning stove.
I figured a RMH instead would be far more handy than relying on the standard AC / heating unit.

Here's the layout of a 7.5 ft x 2.5 ft area I want it to take up. It's spaced a bit from the wall so that the vent and electric outlets are still accessible [see Layout pic].

One downside is that it's located one one side of a ~1250 sq ft house [see House Layout pic].

If room permitting, it'll have a bench for at least one or two butts to sit on.
What concerns me is the total weight the firebricks and cob would have. I went in the crawlspace and took a look at what exactly would be supporting the dead load: [see Crawlspace view pic]

Some nagging questions I have are:
-Before I can even think of building the thing, are crawlspace supports needed for this? How heavy will an RMH of that size be?
-Considering the size and location of the RMH, how much of the house can a RMH of this size realistically heat?

I'm definitely going to attempt to build a prototype outside the house somewhere as a proof of concept for sure, but ultimately, an indoor unit is highly desired.

Thanks in advance!
John

Hi john, I havnt had any luck getting any resposes yet to my question about blowing my face off with a heated copper coil. Id consider putting it on a long wall. From what ive studied, 7 ft is not enough length. Your exhaust port will be very hot. Id put it in the crawlspace and make it the entire length of your house. It appears you have 2 x6 or 8 floor joists. Id definitely put a support beam in. RMH's rely on mass and weigh 2 to 5 tons. I think for that space. a traditional wood stove would be better and easier. You have a tiny house like me.

I would suggest that you change the planned position.The lliving room wall next to the bedroom seems like a better spot. Also a bell would take up less space than a bench and weigh less as well.

> planning...

Perhaps you've factored in these details, but JIC:

You own the property, right? That being the case you can do what you wish (except if you have a mortgage and the insurance company catches wind of non-permitted construction and notifies the bank of policy cancelation), but:

That looks like purely conventional construction which probably means you're in a purely conventional neighborhood which means that resale values will be based on purely conventional standards... Also that a purely conventional buyer will probably employ a purely conventional pre-purchase home inspector with, you guessed it, purely conventional views of home utilities. And of non-permitted additions.

So. It appears that to realize value you must either plan on growing old in that house or just absorb any costs and problems, even losses, as part of the costs of learning and expressing yourself in DIY construction. I'm not knocking it - I've done it for years. Even managed to make a living as a plumber. Just sayin'. It's worth looking at some practicalities in order to not trash your enthusiasm and good attitude needlessly. If you haven't done this stuff much you want to start small - which an RMH in a conventional home ain't.

Your marriage (or "relationship"), if you are in one, is also at very real risk when doing major work on your digs. No kidding, dead serious here. Even with "buy-in" there may come a time... In this regard, it pays to dip a toe into the house-mod commitment rather than do a canon ball drenching everybody close around you. Don't gamble w/what you can't afford to lose and if you don't want to gamble then get buy-in from all concerned and a Plan B, C, D and a final Oops Guess Not exit strategy. Unless you're a batchelor and then it's all cool! <g>

As they say on the invoice, if you've already sent in your money disregard this notice. <g>


Rufus

Hi John ; I agree that the mass location should be on your long wall , that will spread your weight load over many joists rather than your proposed location that uses two. Adding support in your crawl space is relatively easy with concrete pillars and a steel,or wood beam. I also agree with every thing that rufus had to say about ownership ,relationships and building inspectors. Hopefully you are in your new forever home and there is no bank involved because you already paid it off ! Your spouse is more into this than you are ! And you are the building inspector ! HA HA sounds good right ? I can tell you that you are on the right track, these things really do work and they work even better than your hoping. Get a copy of ianto evans book and read up, the possibilities are endless ! Tom

John Trinos : An 8'' system should comfortably heat your whole house on all but the coldest periods, the 6'' is a little small. You should have a back-up plan beyond just
your Fossil Fuel Fired Forced-air Furnace for when the power goes out, The farther into the country you are with fewer neighbors, the longer you will wait to get power
restored after any major storm! Some of your neighbors found out during Winter Storms Clion/ Dion, and neither of them got classified as 10 yr storms !

I agree that an 8'' system will have a Weight of 5 tons if it ran the full length of your house, so- the weight of a king sized water bed over the whole house! Your proposed
model would not weigh as much, but may have to have a bell at the end to trap the last of the heat before it gets wasted going up the chimney !

Ok ! the crawl space, Yes i Would definitely plan on jack posts and a supporting beam, Now would be the very best chance to upgrade your insulation, bringing it down to
the bottom of your floor joists and leaving a small 1-2'' gap above that insulation, more on that later. Right now is the perfect time for you to go into your crawl space and
pull back the fiberglass insulation in several locations From out of the pockets where your Floor joists sit on your sills and meet the sill plate/exterior wall !

You are looking (with a strong flashlight) and feeling for present and past signs of water vapor trapped in these pockets ! New code requires a Closed Cell Foam in these
locations as regular fiberglas/rock wool insulation traps water vapor in these pockets as it condenses against cooler outside walls, The sills/foundation you save will be your
own, this is one of the places were you can go to U-Tube land and learn a lot about dealing with tightening up /insulating your crawl space, some of the work will have to be
done before you do your jack posts and box joists, and much will need to be redone after ! How much of that exterior wall is above the ground and exposed to cold air!
Some times it makes the most amount of sense to put up a waterproof coating and insulation on the outside wall to help to drain water way from your house, check for that!

I would definitely move your rocket mass Heater RMH, to an inside wall more centrally located, as there is a built in cooking feature with the barrel of your RMH. it would
seem natural to locate it In the kitchen against the Wall you have got marked Bath! However it is likely that you will have plumbing in that area!

That leaves the common wall between Living room and Room 1, located here you have the option of having your most distant rooms 2, and 3 at lower temperature in colder
weather !

I. agree with T.R. you can Get I.Evans' book 'Rocket Mass Heaters' used via Amazon or Alibris, or support the creators by going to rocketstoves.com
and Download a PDF Copy $15.00, and print up the number of copies you need ! Review the material, and come back here often. If there is a Rocket in your future we Will
help you find it ! For the good of the craft ! as always, all comments and questions are welcome and elicited! PYRO - Logically Big AL 1

John Trinos : We talked about the weight of your future rocket, we talked about your need for an 8'' system to meet most of your heating needs ! And how to
check your floor joist ends for damage at the sill Wall of your crawl space ! We did not yet talk about protecting the wooden floor from the heat load, or protecting
the 2 x 4 wooden studs hiding behind your sheet rock and other exposures !
Please understand there is so much Crap on U-Tube that I only send people to sites I Know and Trust!

This is a workaround to get you to a special site to view ~3/8ths~ of a DVD that is for sale at village Video villagevideo.org Goto You Tube> and in the search
field type in rocket mass heaters . with the final 's' you should get a prompt asking do you want rocket mass heaters with ernie and erica yes select that
and clickon> the search icon, at the next page you will see a listing of rocket mass heater short videos, select any one marked 'by Village Video', hover your pointer
icon over the 'by village video' until the Village Video>'' Tree in a Field icon'' appears, and click on that, at the next page the very top list of short videos is titled
rocket mass heater scenes find the pointer arrow on the right hand side and make the video selections slide sideways until you come to> 'view all 19 items'
click on and enjoy !

More info at ernieanderica.info ! For the craft ! Big AL !

Thanks for the input, guys! While not in a rush to jump headfirst into this project, I'm doing due diligence first, because the main factors that concern me are fact that the house IS on a mortgage (which I plan to pay off asap) which complicates things since home insurance bureaucracy is in the equation, etc. It's definitely a home I really want to spend a long time in. If that major hurdle somehow can be overcome, I'll be more than willing to proceed.

After looking at the suggestions, the bell design would probably more suitable for the space than the cobb bench. Regardless of which design, I'll need definitely to install crawlspace jacks to support the weight.

As for location, I should've clarified more - the wall between living room and room 1 has a front door next to it, and the wall between bathroom 1 and the kitchen has the backdoor and a mini washer/dryer room next to/in it as well. Otherwise I would've picked those places as the more logical choice Are there any pros/cons to running the exhaust pipe through the ceiling/roof compared to the side wall?

Oh and I do have the Rocket Mass Heaters book. Great material, still in the middle of reading it at the moment.

I'll see what I can figure out. If anyone out there has had to overcome the home insurance hurdle, please share.

-John

> [wall vs. roof penetrations]

Short term, wall is easier. It's lower, easier to reach and usually easier to cut and patch and make weather proof. Long term it's a wash and roof penetrations may look better (or not) and make for better layout for your flu runs (or not). Roof definitely needs to be closed and weather proofed correctly and carefully and this detailing is not as easy for most people as working on walls.

Rufus

If it was me I think I would start out by shoring up the floor turn I'd spray foam the whole underside on your floor, bat insulation really isn't a good product in a crawlspace floor anywhere and you don't really the inside of your house exposed to the unsealed ground (loose poly like you have there really isn't a barrier). You can find your home pulling gasses like radon out of the soil into your home if you don't properly seal the underside.

Then I would move the electrical in the way of your RMH, so you can get it close to the wall and save a bunch of space.

I know it sounds like a lot of work for a RMH but the reality is you'll be much happier and better off for it.

Rufus Laggren wrote:> [wall vs. roof penetrations]

Short term, wall is easier. It's lower, easier to reach and usually easier to cut and patch and make weather proof. Long term it's a wash and roof penetrations may look better (or not) and make for better layout for your flu runs (or not). Roof definitely needs to be closed and weather proofed correctly and carefully and this detailing is not as easy for most people as working on walls.

Rufus

What makes having the wall connection a wash compared to the roof? On another note, the roof is metal, would this complicate things compared to traditional?

Sean Rauch wrote:If it was me I think I would start out by shoring up the floor turn I'd spray foam the whole underside on your floor, bat insulation really isn't a good product in a crawlspace floor anywhere and you don't really the inside of your house exposed to the unsealed ground (loose poly like you have there really isn't a barrier). You can find your home pulling gasses like radon out of the soil into your home if you don't properly seal the underside.

Then I would move the electrical in the way of your RMH, so you can get it close to the wall and save a bunch of space.

I know it sounds like a lot of work for a RMH but the reality is you'll be much happier and better off for it.

How much of a budget would spray foam insulation run for nowadays? I'd imagine I'm better off hiring someone to do that.

I honestly can't tell you how much it would cost, I would imagine $1k as a minimum but that could be totally wrong where you are.

Spray Insulation - You could try Tiger Foam DIY for such a small area. But, it is very temperature sensitive, so be sure either the air or the material is warm enough. A radiant barrier might also help.

One thing that I want to add. Don't let anyone fool you into thinking that poly is a good substitute for spray foam in your application.

I honestly despise batt and poly as an insulator but ESPECIALLY when its used below the surface of the main floor of a home. Just don't do it.

Could you explain what you mean by "poly" in this context?