first post rocket mass heater

So I have an old wood stove that needs to be replaced. I'm not sure if I should put the barrel by the door and make one 90 deg bend in the bench or put the barrel in the corner and have 2 x 90 deg bends and a 180 deg turn by the door? I will try and attach a picture. Please bear with me I'm new here.

Edit: the door in the corner is getting removed.

Not sure if this is too many bends or not. If I put the barrel by the door and just do a single 90 deg bend in the corner I'm worried I won't be trapping enough heat as the bench would only be about 8 or 9 feet.

It doesn't look like you need to worry about bends, as the maximum total length is well less than even a 6" system should be able to handle. The barrel in the corner as your sketch shows would make nearly all of the bench unsittable. I would put the feed & barrel in exactly the same configuration as your current stove, then run the flue out the side of the barrel base to the corner, 90 to run down the long wall, 180 back, 90 to under the wall thimble and up & out. The "J" layout would allow most of the long wall bench to be used depending on how hot the fire is burning. What size is the existing flue? How much space are you trying to heat? Is it a concrete floor... more details of your situation including climate would be helpful.

Check Matthewalker's half barrel system.

Two dead end bells made out of half barrels would give you more exchange surface, so you'd get more heat out of shorter lenghs than pipe!

Like this? Can you give me a link to the half barrel system? River shack, wood siding,no insulation in the walls,some insulation in the ceiling, front addition framed in porch, rear addition cinder block on slab, extra unused chimney in the back. Maybe 24 x 50 or so overall. Current stove pipe is 5 inches I think. Might be six. I will measure when I get home.

http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/#/user/mremine/library/NYC%20Rocket%20Stove%20Build?sort=3&page=1&_suid=1409258461051024995971747774787

Corner view

Kris, what state or planting zone is this cabin it? That will give fellow members a clue as to your heating climate. If this is a full time residence, hopefully plans are in the works to add insulation to those uninsulated exterior walls. Insulation just keeps on paying for itself year after year.

In your photo, measuring from the upper right wall corner, what's the distance between that corner and the beginning of the exterior door to the left, and what's the distance between that corner and the beginning of the second lower door? This will give a clue as to the footprint size for your future RMH.

The available heater footprint will be of help in determining just what RMH design would work best for the available space. It is also possible to do a triple ducting zig-zag run through stepped / terraced mass to fit more mass and duct in a confined space; i.e. Erica and Ernie's Cabin RMH, built in an approx. 4x9 foot space. Check out the schematic for that heater on their RMH plans page here:

http://www.scubbly.com/item/76274

I'm in central missouri(gasconade county, no building code) the squares on the floor are 12" x 12" so it looks like about 5' 6" x 8' on the long wall. The way the house is built, insulating the walls is not within the budget at this time. I understand that's probably the best place to start,but a rocket stove is with in the budget and I don't feel like cutting 7 cords of wood this winter.

Kris, cheap way to insulate your house, you pile up some strawbales on the north wall. Then east and west if you can afford it. Tarp theses. If someone asks you, you say that you're making a stock of strawbales for some reason.

When you make your rocket stove, put some "air entrained concrete" blocks against the walls and on the floor, so you don't loose too much heat to by conduction. You could use an highly insulative cob instead, but that's more labor intensive.

The straw bales is a good idea but it's not really feasible here. Porch on the back of the house,and too much stuff every where else. I would just do light clay infill but the roof eaves need to be lengthened first. Any thoughts on a cast burn chamber/riser? Furnace cement and pearlite in a 1:4 ratio. Or should I just use fire brick? The stove pipe is 6" by the way.

Even if you can't do a wall of strawbales, you could probably put some around the base of the walls in some places. My father used to go around the town collecting trash bags of leaves in the fall, pile them around his house, and next spring he would have a lot of material for garden enrichment.