First off, I've been lurking for about a year but this is my first post...
I have two thoughts that I haven't exactly seen addressed so I thought I would seek your opinions. If they've been discussed before, please forgive me and leave me a link to the discussion. I have Ernie and Erica's book but don't have the Wheaton DVD's and have only made a small temporary Rocket Heater for proof of concept.
1) Sub Floor Pebble Style RMH - Imagine a loft style log cabin here in Alaska, with a crawl space and wooden floor. Would it be a good idea to build a RMH in the corner under the floor with the fuel feed flush with the floor and nothing but a barrel and chimney above the floor? My idea would be to either run a circular mass path or square as long as possible to keep the draft calculations in line. (I figure with a circle I could avoid reducing the length since I would have no 90 degree bends, just one large sweeping circle) This might provide pretty awesome floor heating but would it get too hot? Also, I was thinking the profile of the pebble mass to be V-shaped with the hope that the heat would spread out more laterally instead rising strait up making a hot circle. Obviously, heat rises, but would I lose/waste a significant about of heat into the very cold earth below the cabin?
2) Copper Coil for Hot Water Heater Within the Heat Riser - Like the title says, building the heat riser with a long coiled copper water line inside. I would like to heat water within the copper and run it to an adjacent room/closet with a hot water heater. The water would draw in the lower line, heat up and rise and return out the upper line creating a loop of cooler water drawing in, heating and then returning. I've seen a number of people on YouTube who build a fire around a coil to heat water for a hot tub, it just takes a few hours to heat 100 gallons. I thought by locating the coil within the heat riser, the coil would get much hotter and thus draw more and heat a higher volume of water faster. Maybe a 30 minute burn could heat a 50 gallon water heater? I know the internal temps of the heat riser can be staggering but as long as there is water within the coil the copper should hold up fine right? I could certainly wrap the riser with the copper, or even wrap the barrel with the copper, but I wanted to super heat the water during a short daily burn. Am I asking for trouble and possibly building a steam bomb? Will I melt through the copper? I figure I couldn't run this to an adjacent bath tub/hot tub because I would have to keep it full with water to avoid burning out the copper.
Do the Permies have any ideas or thoughts to contribute to these ideas?