Rocket Stoves Heater/ Outdoor furnace

Hey gang. Listen, I have an idea I wan't to get peoples opion on so here goes. I'm building a rocket mass heater however I want to use ALL it's power. I"ve researched alot about outdoor wood furnances that heat water and I"m wanting to use my rocket stove like wise. I"m wanting to take copper tubing, wrap it around and around the heat exchanger so I can pump water through it to my duct work heat eschanger. Can anyone tell me how hot these stoves get inside their heat exchanger to see if it will heat water running through a 3/4 copper tube aproxtamatly 50 ft or so. Good idea or no.  Thanks for all the info so far. Dabumb

the book does discuss that a little
I'd say try it and let us know
with one warning, a closed loop of copper tubing when heated by an uncontrolled fire will eventually develop enough pressure to explode, and a steam explosion inside a space where you are standing is something you want to avoid, so either keep the loop open somehow or invest in a good relief valve and put it outside of the people space

I found some firebrick from an ole chimney that was demolished. It's the red clay bricks. Does anyone know if they will work for a rocket mass heater like this one.

This is what I'm building.

Dabumb wrote:
I found some firebrick from an ole chimney that was demolished. It's the red clay bricks. Does anyone know if they will work for a rocket mass heater like this one.

They will work. They will stand temperature just fine. They will last less long than true firebrick right in the burn area. Here is an article that talks about it a bit:

http://www.pyromasse.ca/rbcc_e.html

I had thought there was another that fit better but I can't find it just now. The thing to remember, is that these guys are building an Expensive heater that is designed to last the life of the house.... and they will get call back 10 years down the road... Also, They get paid by the hour and using the same brick all through even if it costs more may be less expensive than using two different sizes and doing more work to fit. (clay bricks are 7.5 inches long, fire brick is 9)

However, there are red clay fireplaces from the days of daily hot fires that are still standing and working hundreds of years later. As the article says the main thing seems to be the CO reacting with it... by the top of the riser all that should be burnt and reburned away.... but form factor of the brick would make it hard to fit with the rest. (read that as really hard to seal)

In short, choose one or the other. Also be aware that if you are using plans that use fire brick, you will have to be willing to "re-engineer" things to get the same size from smaller brick.

Awesome... I can get this bricks for .25 each so I'm gonna load up on them.  Thanks for the info.

I do also recomend using all the same brick because of different expansion degrees.

There's a video on youtube where a guy use's 2 different bricks and they seperated.

ya and that system has a few things no in the pictures that make it so it wont explode.

1. the water at mt home is gravity fed at about 15 lbs pressure.
2. the hottest part of the coil is at the top so when it gets a stem flash it helps pump the cool water up the coil.
3. the temp in the stove at that point is 2500 degrees.
4. there is a restrictor in the piping so that no one can close any valves to the gravity tank.
5. the system always circulates there is no shutoff.
6. the coil was sized very specifically to that size of stove.

if you didnt understand any and all of that then you should not be trying to make that version of water heater. I will not go into any more detail here because if you get it wrong it will blow up in your face. Since that is my design and stove, Rest assured that i bloody well know what i am talking about.

OK  I found some old firebrick from a chimney that was torn down. I"v got my brick all ckeaned up so I"m ready to start my build. The old brick is only 2 1/2 inch by 8 so ;it takes a big more brick but I'v got plenty.

I'v been doing some research on "On Demand Water Heaters" where they instantly raise the water temp 60+ degrees in just a couple of seconds.

I personally don't feel there will be any problem heating water in my rocket stove sence the burn chamber is suppose to be around 1500 degree's.

I"m going to set about a 25 gallon tank of water (old water heater tank cut down) on top of the stove to be pre-heated. Then come out of the tank into my circulating pump 3/4 inch pipe.  Out of my pump into a 1 1/2 inch pipe that I will send through my heaters burn chamber. After exiting my burn chamber I will again go to 3/4 pipe to slow the water down for heating and to my heat exchanger and back to my holding tank.

This will NOT be a pressurized system. If there's any failer with my pump, the water should just perculate untill the fire goes out.

I'm hoping with using a 1 1/2 black pipe line, that will give the water time to heat up.  My goal temp is 160 degree's + or -  ten degree's.

I know this is trial and error but thats what were all about  right???

I"ll post my results as I go and I"m allway's open to idea's.

Dabumb.

To maintain a clean burn and reduce the chances of a steam explosion (especially since different firewoods or weather conditions affect the temperature and speed of the burn), we are considering a system that would take the heat off the manifold or heat-exchange area, _after_ the initial burn and downdraft areas.

In Smith's video, this would be in the cob part of the installation.

Outdoor wood boilers are notoriously smoky because burning a fire in a water-surrounded tank means the fire never gets hot enough for complete combustion.

So letting the burn area (fuel feed, horizontal burn tunnel, vertical heat riser) stay hot and insulated, and then plumbing the copper tubing to capture heat off the downdraft or subsequent exhaust paths, would promote clean burn.  On our systems the exhaust is down to about 5-600 degrees at the junction of downdraft and cob bench, hot enough to warm the water but much less likely to create steam explosions than the flame path itself.

Please post pictures or a report on how it works out!

-Erica Wisner
www.ErnieAndErica.info

Quick question.  Should I use regular mortar for my firebrick, or Refractory cement? Seams I"v read where people have used both so I"ll ask the experts.  Thanks.

I'll try to post a pic or 2 soon as I begin my project.

Dabumb wrote:
Quick question.  Should I use regular mortar for my firebrick, or Refractory cement? Seams I"v read where people have used both so I"ll ask the experts.  Thanks.

I'll try to post a pic or 2 soon as I begin my project.

Refractory, or fireclay (clay-sand or clay-brickdust), or local clay-sand mortar.
Avoid cement or lime mortars unless specifically designed for high heat (upwards of 1000F, possibly as high as 1800F or more).

If you can set the firebrick plumb and level without mortar, and stabilize it from the outside, that's a good way to go.  No mortar = no different expansion rates or repointing to worry about. 
But you have to get the base level, and provide an exterior seal and support.  Protect not just from heat and gas escaping, but stabilize the bricks against the usual thumps and bumps of fueling and cleaning. 

We use Oregon-style cob and perlite/clay insulation for this, works pretty well if done carefully.