Introducing myself

Hi everyone,
This is my first post here I have been reading posts for some time and even made an account some time ago. I just wanted to stop in and say hello because I am just about to start collecting materials and building a rocket mass heater for my house.
My wife and I have been planning this build all summer and each of us have our own concerns. She is mainly concerned with initial cost, operating cost, and how it looks when it is done. I have the same concerns but safety and building are my biggest concerns. We will have to purchase all of the materials to build the heater so our up front cost will be a bit high but operating costs from what I can see will be significantly less than what our heating bills are now. We heat 100% with electric heaters and last year we had 2 months that cost $500 and 3 that cost $300.
We live just south of Dallas Tx. so our winters are not terriable but being low income any savings would be wonderful. I will be doing the build myself because we are new to the area and do not have any friends that can help us with this.
The basics...
I have a 1971 trailer home that has an addition. It is a 76 foot long by 14 foot wide trailer with an addition of 25 feet by 30 feet at one end. So it you were to look down from above it would kind of look like a lower case b. I plan on putting the rmh in the end of the trailer that has the addition and venting the exhaust outside into the carport that is on that end.
So the rmh footprint would be about 13' 3" long by 30" wide on the small end and as wide as needed on the barrel end.

So my questions are these;
Most builds use 6" duct but some use 8" is one better?
Is there a certian type of clay that is better or will any kind work?
What is the propper head space between the riser and barrel? From what I am seeing it is 6" is that correct?
Morter between the fire bricks is plain portland cement? or do I need to add something to it to keep it from cracking?

I am sure I will have more questions so any help will be greatly appreciated.

I built something that may resemble a rocket heater, I went with about two inches between the top of the riser tube and the top of my stove, I have a 4 inch riser tube, I believe I think I could have used a little less space, some place I remember seeing that you can go as close as 1/3 the size of your riser tube, so if you have a 6 inch tube you need atleast 2 inches.

Clifford,
Thanks for the reply I am still a bit fuzzy but Am still doing research.

Curt Hettman wrote:
So my questions are these;
Most builds use 6" duct but some use 8" is one better?

The larger the system, the more heat output potential

Curt Hettman wrote:Is there a certian type of clay that is better or will any kind work?

If you are referring to the clay used to cob your thermal battery, the better clay is one that can be packed with the most density.

Curt Hettman wrote:What is the propper head space between the riser and barrel? From what I am seeing it is 6" is that correct?

The gap here is best kept at a CSA (cross sectional area) to match your system. The math goes as such; circumference X height = CSA of "imaginary ring". So, a 6" has a circumference of 18.84" and would be best at 1.5" gap where as an 8" has a circumference of 25.12" and would be better at 2". With that being said, adding a 1/2" would allow more heat to pass from the barrel into your mass/exhaust.

Curt Hettman wrote:Morter between the fire bricks is plain portland cement? or do I need to add something to it to keep it from cracking?

Fire bricks are designed to withstand high heat, plain mortar is not. A refractory powder mixed to the consistancy of pudding and applied thin as more of a slip to seal brick to brick will last the longest.

Hope this helps

Martin you are the man. Those are the exact answers I was looking for. Now to just find a good source of all the components near Dallas.