James (cob workshop) is planning an interesting rocket mass stove using a gas hot water heater. I hope he’ll continue to share his progress in designing and building his system.

My meeting with James this weekend provided lots of food for thought. This post is mostly just ideas, with a bit at the bottom regarding plans.

My brain doesn’t stop processing ideas. Something James said yesterday triggered an extension of my thought on a kickoff fan for hypocaust (obviates the need for a priming fire and solves the draw problem until the burn chamber heats up). To get a fan that will provide the proper amount of airflow (enough flow to keep the air moving but not so much it will put out the fire), the fan will need a potentiometer/rheostat. If you haven’t been following my posts you won’t know about my interest in hypocaust floors. Check out my original house site for more information

Because James mentioned cleaning difficulties for exhaust run through the floor, we had a brief discussion on air to water heat exchangers. I talked to Dan (brother) yesterday about water based heat exchangers. We kicked some stuff around, but the visit was too short (time enough for dinner and a rub for all the dogs) and we ran out of time. I’ll hit the topic again when we’ve got a bit more time and the two of us aren’t quite so tired. I’ve got to run up in the next week to get the last drive shaft parts for the mixer. Dan is a pretty amusing guy. Here’s his solution for a bucket brake (mixing cement for ferrocement).

On the heat exchanger topic, water based cooling systems for computers use air to water heat transfer. I’ve looked at a bunch of those systems while researching cooling for my computers. There might be some concepts of worth there. Radiators are fairly easy to come by and would be no problem to chain together. It would be worth experimenting to see how plugged they would get . . . As the system I’m planning doesn’t run to the need for heat exchangers, anything I come up with is strictly conceptual.

As to the whole concept of heat exchanger and rocket mass heaters, every idea I come up with ends in a complex multi-staged system. I don’t see that as being value added. Any system that transfers heat more than once isn’t going to be very efficient. I think it would be far easier/less expensive to plan how to clean the hypocaust portion of the exhaust. I know there are ways to vacuum all the hot air ducts in a home heating system. It shouldn’t be too hard to adapt that concept to cleaning a hypocaust exhaust system. And with welding skill, it would be possible to add cleanouts in appropriate places.

I think the rocket stove would burn better/cleaner if the burning end of the wood is held off the ash pit by a grate. The test I tried certainly did. Toward this end, I’ve been researching grills. I want to plan my rocket mass heater feed tube to accommodate a grate. I’ll have to do a bit of experimenting to find the right depth in relation to the feed tube. While doing research on grates, I ran into a great paper on the longevity of different materials for downdraft grates. As I can’t afford (and can’t find) RA330 alloy, 304 stainless, or any of the other really effective materials tested, I’m going to have to stick to what’s already formed, inexpensive and will work . . . hibachi grills. I should be able to find them at low to no cost and will plan my rms accordingly.


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