Tom Riker

With the new information, numbers look WAY better!

347*.25*30=2595 or 2.6kw/hr

I am in the 200 mm range!

Looks like I'm building me a RMH!

Now to get the videos!

Okay. I think I figured out what an insulation factor is. It is called a K-factor here.

You can figure it by dividing the thickness in inches, by the R-value.

A straw bale is roughly 16" thick. It has roughly R-30.

16\30=.53

My dome has R-21 in 5.25"

5.25\21=.25

I hope this will help someone!!!

I would just like to add my two cents to this discussion on boric acid. Yes it is toxic. But you must look at the amount required to cause harm. It takes nearly "half a pound" of boric acid to kill a person who weighs 180 lbs. In comparison, it takes the same amount of table salt to kill the same person.

This is not to say that it is completely safe. DON'T EAT IT!

RV antifreeze, propylene glycol, is used in all sorts of food products and is determined safe for human consumption.

It absorbs water, yes, but it binds with the water making it non destructive to the wood.

I use these chemicals to make wood preservative.

WARNING!!! propylene glycol is basically an alcohol and has a flash point so use it at your own risk of fire.

What I do....

I place one gallon of propylene glycol in a stainless steel pot that is at least 3 gallon capacity.

I bring this to a "roll". I don't bring it to a heavy boil due to "flash".

I then add one pound of boric acid. stirring it in slowly to help it dissolve. It will not dissolve completely for a while so don't be alarmed.

Once it is pretty dissolved, I add one pound of 20 mule team borax. Stirring it in the same way.

At this point, there will be "grit" in the bottom of your pan. Just keep stirring until the bottom is no longer gritty.

Apply while hot, as it will get lumpy when it cools.

SO.... What does this actually do?

This mixture protects your wood from rot..... The Borax, (boron salt) protects your wood from fungus, mold, etc..... The boron protects your wood from insect damage..... and the propylene glycol protects the wood from water damage.

If you have ever seen "green board" on tv shows like Mike Holmes, this is the same stuff only home made. It is CLEAR, and you wont see it. The green board has a dye added so it can be easily identified as treated.

I used this while building my dome home. My house is now protected from the inside out against rot, bugs, and mold.

Thanks Glenn. I live in Indiana so it may be 65 one day and 30 the next.  I have access to plenty of wood so I am not concerned about the amount of wood I use, except for the simple fact that I don't like wasting it either.

My wanting to use this type of heater is that it burns so much cleaner and is more efficient with the fuel it does use.

I can fire three times a day easily.

Currently I burn continuously at an "idle". It is VERY dirty and I get ALOT of creasote build up.  Bad for the environment. Bad for the flue. And I use a lot of wood.

I could heat with propane, but I really like the wood heat.

Thanks for explaining about the mass sizing, I think I should keep the mass to a medium size because of the frequent changes in climate. ( Oh no....climate change)

Thank you for the reply.

Since I didn't know what an insulation value was or how to figure it, I took a guess.

The only figure in that list that I recognized was the straw bale, at .5.

I know that a straw bale averages R-30 here in the States. Considering that I have R-21 and the Dome itself requires less energy to heat and cool, I should be VERY close to that.

Using the .8 figure gave me a 9 inch batchrocket.

I am thinking of building an 8 inch batch with bell and a mass bench. Any thoughts? I also have a brand new Mitsubishi ductless heat/air pump that I can use as back up heat.

I also wonder how much mass to use.... is there a ratio of rocket size to mass? I am in the process of reading batchrocket.eu. It is probably in there.  I am guessing about 3000 pounds

Thanks for the replies.

Perhaps the insulation number is my issue. I chose 1.6 insulation factor because it was a guess.

Since a dome is all roof, I put grace membrane over the entire dome, so it is literally air tight with the exceptions of doors and windows. (  grace to seal around them too)

Since it is built from 2x6 lumber, my insulation is R-21.

All the literature I have read says a dome requires 30-40% less BTU to heat and cool. Add to that my complete membrane; I believe I should be very close to that.

Would R-21 and an air tight home give me a better Insulation factor than 1.6?

I currently stay in an mobile home that is VERY drafty and poorly insulated and my only heat source is an "Old Timer" wood burner with an 8" flue. This thing will run me out of the house if I fire it up and open the draft. I can only let it idle. I currently am burning around 4 cord per heating season.

I would like to use a batch box with a bell. I have enough room for a bench if needed. my floor is unfinished concrete, fiber reinforced at 4" thick. Height is not an issue because the ceiling at that location is 14'.

Thanks again for any help.

I have bought the book from Paul about building RMH. Is there a book that covers how to build batch box with bell? Maybe a set of blueprints for a known good design?

So I have looked at the batch box style and think that is the way for me to go.

I have seen all the ways to figure up the size of the stove, with the exception of how to size it to the house.

I have seen one formula: Q=G*V*DT

Where Q is the amount of Kw required

G is an insulation factor.

V is the volume of the house (m3)

And DT is the difference in temperature from outside to inside.

I have a dome home that is 36' in diameter.

That gives me a Volume of 346 m3.

For my house I chose to use the insulating factor 1.6

and my DT is 25 degrees celsius.

According to that formula my Kw requirement would be 13840 or 13.8 Kw

According to the chart, there is no way for a batch box to heat my house.

The bigger the internal diameter, the heavier the load of wood for each fire:
Internal diameter (mm) -- Wood load (kg) -- Mean power considering two fires a day (kW)

   125 mm — 3.5 kg — 1.1 kW
   140 mm — 4.9 kg — 1.5 kW
   150 mm — 6.0 kg — 1.9 kW
   175 mm — 9.5 kg — 2.9 kW
   200 mm — 14.2 kg — 4.4 kW
   230 mm — 21.6 kg — 6.7 kW
   250 mm — 27.8 kg — 8.6 kW

Considering that a 250 mm stove is a 10 inch stove.

There must be a problem with either the formula or my math skills.

My numbers are:   Q= 1.6 * 346 * 25    so Q= 13840

Can anyone advise me on this? What have I missed?

Thanks in advance.

I really want to use one of these.

Thanks for the reply. I just looked at your link and think that may solve my problem. I need to read everything there, but it looks like that is what I need. Thanks!

This may have been answered before, but I can't find it.

I am building a 36" dome home. Concrete floor covered in wood flooring. Except around stove.

My concern is:
A 6" stove with a 55 gallon barrel seems like an awful lot of heat will be released at the barrel. It is my understanding that this heat loss is a MUST for this stove to function properly. My dome is VERY tight and well insulated. I am afraid that the amount of heat coming off the 55 gal drum will over heat my house while I am trying to heat the mass.

Is this something I will just have to deal with? Open a window during burns? Or am I over thinking this?

If I am going to build one of these I need to "dot the I's". I have bought the book for building rocket mass heaters and am thinking of the videos now. Perhaps watching one being built will answer the rest of my questions.

Thanks in advance for any comments.

I just bought the rocket mass heater book and am going crazy with all this.

I will stick to what the book says. Thanks for the replies.

I am in the process of building a dome home and I think a rocket mass heater would be a great addition.