Alecs Farca

While #3 is the safest, will it provide enough power ?
I'm leaning towards Dave Lot's system (https://permies.com/t/40107/rocket-stoves/hot-barrel#353442) that I like - it's already implemented and tested for output (and safety).
He's been heating 73 lbs. of water (~9 gallons) to max 140F in 2-3 hour burns. From the pictures seems to be ~42 feet of 3/4 copper wrapped on the outside of the barrel.

Thank you for the replies (also got a PM from allen lumley).

On further investigation decided it is safest to go with an open system (using an open expansion tank like so - http://www.deppmann.com/2011/10/30th-4/).
So, in an open system which one of the 3 flavors would you choose for a 'standard' 8 inch system (55 gal drum, 23 feet long horizontal pipe, ~20 feet long flue) ?
I am worried about the impact off adding either #1 or #2 - gases getting to cold, creosote build up, inefficient system - Dave Lot says #2 helps the stove 'really take off' while Ernie's opinion is that 'it cools the system too fast and you get soot'.
Ideally the coil would heat my 10 gallons of water to a temp of ~170, I have seen 160F in a 5 gallon system (https://permies.com/t/40107/rocket-stoves/hot-barrel#343291) so that should be possible.
I'm guessing #3 is to weak/slow for that.

Few clarifications:
a) Electric-powered boiler can heat water through a resistor and one(or two) water coil(s): http://www.panosol.ro/images/Boiler%20bivalent.png
b) I have experience in plumbing, have also used pressurized stove water heaters (https://kotly.com.pl/produkt-boiler-viadrus-u22-s-hercules-33-kw-3084.html?l=en), setting it up once I have the plan should not be a problem.

I need to eventually answer the initial 3 questions:
1. Go with #1 or #2 ? or as a last resort #3...
2. How much 3/4 copper to use in case #1 or case #2 ?
3. How would any of the 3 cases affect the system ?

Hi, my name is Alecs, and last year my wife and me have successfully built a couple of 8 inch RMHs (by the Ianto Evans book) in an old wood frame + cob house. We also have 2 small rooms upstairs and an electric-powered boiler that we would want heated from one of the rockets.

Have done some research about where to place the heat exchanger (copper coil):
1. Wrapped on inside of barrel
http://www.rocketstoves.com/wisner.htm
https://www.youtube.com/watch?v=gq0d_hL5X9M
https://www.youtube.com/watch?v=HnbSCR6RTb0
2. Wrapped on outside of barrel as I've seen you mentioning and seen implemented:
https://permies.com/forums/posts/list/40/5937
https://permies.com/t/40107/rocket-stoves/hot-barrel
3. Wrapped on 1st 5 feet of exhaust as I've seen Ernie recommend here:
https://permies.com/t/12179/rocket-stoves/rocket-stove-water-heater#276477

- Would rather go #1 or #2 because it would just be easier to add to what we have now.
- 3/4 inch copper coil seems best, not to pricey and harder to flash to steam.
- I would be using a small recirculating pump backed up by and UPS if the power runs out (rooms being upstairs, the system will benefit from thermosyphoning as well)
- plan on installing 2 pressure release valves, manometer, thermometer. We feed the RMH at least every hour or so, I think there would not be a problem with it overheating before we can put out the fire in case of an extended power out.
- I've read Dave Lot's posts @ https://permies.com/t/40107/rocket-stoves/hot-barrel and I think I've also seen Erica Wisner mention that the system would benefit from running cold water around the barrel
This is contradictory to what Ernie is saying:
'Dont put a coil around the barrel put the coil around the exhaust and use the thermal siphon. dont put a jacket around the barrel it cools the system to fast and you get soot' @
- from my calculations the system would hold about 10 gallons of water

What I have not decided on and would like to hear your input is:
1. Go with #1 or #2 ? or as a last resort #3...
2. How much 3/4 copper to use in case #1 or case #2 ?
I have seen Ernie (and others) use 20 feet half inch for #1.
While for #2 60 feet, 40 feet.
3. How would any of the 3 cases affect the system ?
My understanding is that ( as Konstantin Kirsch best puts it @ https://permies.com/t/32099/rocket-stoves/doubling-power-RMH-cooling-feed)
'A RMH has minimum 2 pumps: First the heat riser pumpes the hot air up. Second the barrel pumpes the air down on heat exchange over the surface.
If you do have a vertical chimney than you have a third pump.'
So the system would benefit from either #1 or #2.

Hope to hear your thoughts,
Alecs.