Advice for building a batch box RMH in Western Massachusetts

I am getting rid of my natural gas furnace and stove (assisted by the lightning strike that made the furnace unrepairable).

I will be putting in a mini-split heat pump, but I would also like to put in a batch box rocket mass storage heater in my basement as a way of reducing how much I have to rely on the mini-split, like if the power goes out, or in general to help keep the temperature up so the mini-split doesn't have to work so hard.  My house is just under a thousand square feet, one story plus the full basement.

I'd like to choose a simple, well tested design, but I also need to pick a design that will play well with Massachusetts laws.  I've got a copy of the Wisners' Rocket Mass Heater Builder's guide, but it has so much information I'm overwhelmed.  It would be a great help to find people who have built rocket mass storage heaters in Massachusetts who would be willing to talk to me.

I can probably manage the build myself, and I might even be able to find a lot of the dirt materials on my property, which has very fine, silty soil, but it would be great to have someone show me what kind of soil I'm looking for so I can figure that out.

I'm also in W. MA and would be interested in learning/helping/ observing this if possible!  

Hi, Heather -- I would enjoy collaborating. What kind of building are you wanting to heat?

Hi Judy;
Welcome to Permies!  And Welcome to the wonderful world of Rocket Science!

We have another Rocket Scientist on staff who lives in New York State.
He may be able to guide you with finding supplies and possibly with state law compliance.
I'm sure he will post soon and have some local info for you.

As far as your build.  
A 6" batchbox is a good choice.
You have a choice of a traditional piped mass or a Stratification chamber.
A stratification chamber is nothing but a large empty box that vents from the bottom.
It can be built in many ways, but by using red clay brick for it and your core it becomes very easy to consider/call this a masonry stove.  
State law varies regarding building a masonry stove but at least there are rules.
If you say Rocket Mass Heater they will not know how to proceed.

To give you some examples. Here are links to my posts about rebuilding a 6" and a 7"  Batchbox.
The 6" has a more traditional piped mass and the 7" has a brick bell.
https://permies.com/t/181421/Batch-box-rebuild
https://permies.com/t/187667/Studio-Dragon-Batchbox-Rebuild

You certainly can build this yourself!  
Although it would be more fun with a helper (Heather maybe).
We can help guide you with specifications and real-world experience on what to do (or not do)  
You will not need much if any material from your yard.
Cob mortar is 3-part sand to 1-part clay.
Buy 50# sacks of dry fire clay at the masonry supply and 100# sacks of commercial builders sand at Home Depot.
This makes the best cob mortar.
The same masonry supply will sell firebricks, you'll want 35 full-size heavy bricks.

That's enough information for now.
Tell us more about your basement layout & your class A chimney plans.
Photos are always appreciated.

My basement is dirt floored, with 7 foot clearance under the floor joists, and completely open.

There's a chimney that is currently not used for anything -- I haven't measured the flue size, it's not a big chimney, and it goes up to the peak of my roof, ending about 10 inches above the roof.  It used to be the vent for the old gas furnace, but when they put in the new one they put PVC pipes out the back wall.

I'm thinking the chimney might be useful for the RMH / masonry heater build.

Hi Judy;
Please check your chimney size.
You need a 6" minimum for it to be able to be used.

Massachusetts law has no relation to NY State law, so I can't advise you with certainty, but if they use the International Building Code as a base, there are provisions for masonry heaters that can be applied to rocket mass heaters. Just use the term "masonry heater" in any conversations with officials. The trickiest potential part is that a masonry heater is supposed to be built or supervised by a recognized professional, which might be taken to mean accredited by the MHA (Masonry Heater Association).

Hi Alaska, I am just east of Binghamton, and would be happy to chat in a week when I get home and settled from a couple of weeks away.

My chimney flue is 8 inches in diameter, exactly.

I think I should get a chimney person in to tell me what kind of shape it is in, it hasn't had any attention in a couple decades, being out of use.

I will look into the MHA -- masonry heater association -- and see what kind of supervision might be available.  I'd like to do as much myself as possible, partly for cost but also for the fun of it, part of which is really understanding it well, which happens best when I make something myself.

But  I would very much also like to get it right and not have any bad things happen to my house.

If anyone knows of anyone who would be a good supervisor, with the requisite credentials, I would be delighted to be referred to them.

Hi Judy;
That's great news your chimney is 8"
Having an inspection done is a good idea.  
Be aware that the inspector will base their recommendation's on a normal very hot wood stove fire.
They will not understand that your RMH will only have exhaust temps in the 150F range.
Your chimney needs are less.

There is a chimney and heater company that also offers masonry heaters, about an hour south of me, so I'm thinking I'll ask them to inspect my chimney; I'm hoping they'll have a clue about exit temperatures.

At the moment, I'm thinking I will take advantage of the incentives for heating systems and get a heat pump, as much to have a backup for if I travel during the winter.  But heat pumps annoy me, they only go down to 60 degrees, and I prefer a range from 42 to 55, depending on what I'm doing... sleeping at 42 is my preference, so I don't heat my bedroom at all; but for sewing and other handwork, 55 is about the minimum.  There is a Mitsubishi model that has a 50 degree setting (I read their user guide), so I'll probably get that one.

However: one part of my thinking is taken from looking at Uncle Mud's basement heater for Gracie, in northern Ohio; the average winter temperatures there are close to what I get in West. Ma.  That's a 6000 sq foot house that's being heated, and mine is a mere 960 square feet, but I like what she says about having warm floors.  For a number of reasons I don't want to put the heater in my living space.

I'm also looking at https://batchrocket.eu/en/designs... probably one of the octagonal fire brick types, which seem like a better bet to me than the cast designs.

Given that I have a dirt floor basement: can I build the heater on levelled dirt, or do I need a concrete pad to put it on?

Hi Judy;
You would want to pour a small insulated slab for a batchbox and bell to sit on.
You want all your heat going up, not trying to go down and heat the earth.

A comment that I have gotten is that putting the heater in the basement, I'd be heating my basement walls and house floors, but not the house.  

Is there something I could do about that?

I've also gotten a very rough estimate for a masonry heater, in which the stove itself is $15000, and the labor to put it in -- it would be a 24 inch diameter Klein Kagelofen in my kitchen -- the labor and other refitting cost would be $10,000.

However, the guy I got the quote from says that a rocket mass heater is not going to pass code in Massachusetts.  I feel in a bind, that's a c-load of money to spend for a certificate of inspection...

Judy

Judy, Just last winter, a fellow Permie in Mass. installed a RMH based on the Liberator rocket stove. Uncle Mud has a few videos of the build, I was there midway through the build to help, and deliver some materials. I could PM you their info, I think they would be happy to talk about it.
The Liberator stove is UL listed, though it's not a batch box, there is a pellet feeder option, I think?

You say "full basement", and also "dirt floors"... so, not "finished space" that you would be occupying (unless some severe circumstances occurred?)  If the heater was upstairs, in the living area, would it need to be a batch box? I'm guessing that you are considering a batch box would require less tending, therefore fewer trips down cellar? If the basement is unfinished, you could easily build the structural support required to put the heater and a mass upstairs, no? Assuming that old flue is in an advantageous location...

I'd be very interested in talking with the Liberator build folks!

The choices of where to put the thing are very much up in the air.  

One of the things I find daunting is building up under something to support it on my floors, but you describe that as easy. Really? what kinds of materials and building skills do you need for building the footings for a RMH on the main level of a house where the floor joists are seven feet up?

Hi Jenny;
In your situation with a dirt floor, adding adequate support is not difficult at all.
You would need several concrete pier blocks with a 4"x4" placement in the center to set your vertical 4"x4" into.
The idea is to place a support under your floor joists.
The pier blocks should be partially buried so they can not be bumped.  Vertical 4"x4" beams support a 4"x6"  horizontal beam that is supporting multiple floor joists under where you place your mass.
You will not need to jack your floor up, simply place your 4x6 snug to the joists.   The added weight of a mass will sit happily on top and your floor will be solid.
Note)  This is a simple description,  Your verticals need to be tied into your existing structure and your horizontal needs to be attached to the rafters.
A competent handyman-type person could easily direct you on how to proceed.

Here is a link to The Liberator stove site    https://rocketheater.com/products/the-liberator-gen-2-without-hopper

The Liberator uses a rocket stove design and it can be connected to a mass to help hold your heat longer.
But the amount of mass a Liberator can heat is much smaller than a conventional batchbox or a J tube can heat.
A Liberator can push 12' of the horizontal pipe.
A 6"  J tube can push 35'  
An 8" J tube can push 50'
A 6" batchbox pushes 50'.
The liberator can burn pellets or wood.
The Liberator is completely legal to install and would have no weight issues even with a 12' mass attached.
You would not want a Liberator in the basement but upstairs where you can easily load it.

Thank you, that is very helpful!

This is how I see it:  There would be one 4" x 6" horizontal beam right under my floor joists, crossing as many of them as I expect my heater mass to go across.

Then there would be some number of 4" x 4" verticals, each with a concrete pier block big enough to fit one end of the 4" x 4" into securely; each pier block dug into my floor.

Two verticals? four? I'd probably go for four, as I generally prefer to err on the side of overbuilding.

I think I'd make me some 2x2 strips (halved 2x4's) and screw them to the tops of the 4x4's and also screw through them into the 4x6.

And more short lengths of 2x2, screwing one end into a joist and one end to the side of the 4x6.

How does that seem as a plan?

Hi Judy;
Yup, you have it figured out.
As far as how many vertical 4x4s that would depend on how long your 4x6 needs to be.  
At 8' long I think 3 vertical would be plenty. At 10' four should be enough.  
They do not give lumber away cheap anymore!
No need to buy treated wood, but you do want structural grade fir and larch wood.  

Hi Judy,
Wish I'd seen this sooner.  I am the one who installed a Libeator with mass, and thanks for not outing me before I was ready, Chris.

It is fully permitted and everything now.

It kinda sucks compared to a _real_ rocket mass heater--I went through 2 cords of wood the first winter, about 1.5 this winter--but it's gotten us by.

I'm in current machinations process to get my town to allow real rocket mass heaters.  

Glad to collaborate, and again I wish I'd seen this sooner.  I'll send you a purpoe moosage.

Joshua

Hey Josh;  Call them a Masonry stove, not a Rocket stove.
Perhaps a Montana Masonry stove?