Brad Weber

bob day wrote:The other thing that occurred to me concerned your seal of the front door.  If your house is pretty air tight you may be creating a partial vacuum inside pulling back on the draft.

This is a very important and often overlooked point. Any building that has an exhausting appliance works on a vacuum system. There are some locations that require
constant building vacuum systems for things like radon. Your mass heater has to pull against that draw to perform. Your building may have several air drawing items working at once. Consider if you have things like a gas hot water tank, gas furnace, dryer running, attic fan running, stove hood, bathroom fan or another wood stove or fireplace. All of these things will draw air out of a building and for every cubic foot of air that goes out the chimney, a cubic foot is drawn in to the building from somewhere. Your heater WILL have to deal with this.
Brad  

Michael Solosky wrote:Brad Weber, thanks for the idea! It may be just the thing to get it flowing in the right direction after I make a few modifications. I have a 6" duct fan that I think I'll Mcguyver into the system and give it a try. Cheers!

What ever you do has to fit certain parameters. It has to help with the draft. It can not, in any way, interfere with the flow of air when not used. It has to be comfortable with high heat. A motor and fan in-line just won't do it.
Brad

This is something I had to deal with a lot. I have an external chimney and had no choice but to deal with it. Here's the bottom line, if your chimney is cold it will not draw. In fact it may push back. I dealt with this in two ways. One is to make sure that the chimney is well insulated. If the chimney is single layer then the heat will dissipate through the sides and as it does the air will not want to rise. The chimney wants to be warm to rise and the warmer, the better. So even if you have good fire starting and the system is drawing, the heat going through the system will be dissipating rapidly, and not warming the chimney, until the whole system is up to running temps. The second is to have a way to force the draft. I use the venturi method. In the garage heater I drilled a 1/4" hole in the side of the exhaust pipe. I have an air compressor so air pressure is available. I shoot a stream of compressed air upwards through this little hole, and through the siphon effect, draws air through the system and up the chimney weather it likes it or not. This allows the fire and heat to flow through the system quicker so the hot air doesn't have time to be cooled by the mass and warms the chimney. This may have to happen two or three times until the chimney is warm enough to stay warm and flow. In the house heater I built an air pipe that enters the chimney clean-out and then goes up the chimney to just below the heater entry point. The clean-out opening was then filled with fiberglass to stop all air infiltration. I use an air mattress pump to blow a stream of air up the chimney. This does the exact same thing as the garage system, drawing air through the system and warming the chimney. In the picture you can see the pipe along the wall that enters the clean-out.
Hope this helps, Brad

Hello Sonny and congrats on a cool design for your house. I have concerns with not insulating under the heater. I built one with the same thoughts as you that the floor would also act as mass. Boy was I right. The problem is nothing was done in advance to insulate under the cement. I see you did this also. The Earth is a heat sink and some of your heat will go through and keep going, never to return. Insulation under the mass or even better, elevation off the floor will go a long way at keeping the heat of your mass inside the room. Then the concerns of using building structure for heat. Will it take the expansion and contraction of the high heat and then cool? Was it built for that? In your case it might be fine. You will have to see. I would also like to have the chimney pipe exit higher if not right through the point. The ceiling will be the warmest there and the pipe will draw wonderfully even on cold start. Insulated pipe through the masonry and above.
Brad

Your engine will never get extreme heat like a rocket stove can produce. Consider that iron and steel start to glow red on their own at or just below 1200 degrees F and you have never seen any of the motor glow red. If you did it was right before it exploded. Now I regularly can achieve over 1600 degrees just in the burn area around the burning wood. You can do a test yourself by putting the end of a straitened coat hanger down into your fire and let it soak for a minute. Pull it out and it will be orange. Dull orange is 1400 degreesish. A bright orange and you are 1600 degreesish. You only have to rise another 800 degrees or so to start to burn the steel. I am a blacksmith and I do understand iron and steel at high temps.
Brad

Cool idea but the thermal dynamics of the chamber won't be friendly to cast iron. Yes it will work and work well at first but the material will melt when it gets hot enough. Cast would have a nice rough surface for turbulence and is designed to stay rigid while hot up to a melting temp. These heaters can get hotter than that in the burn area. Then the want for a smooth inside to your heat mass would also suggest the cast is not the best choice.
Brad

The 6" system works fine and the end result is the same. I burn small amounts of wood and retain the extra heat in the mass. My goal is to try to keep the shop at 50 or above and the heater keeps a warmth all night. In the mornings I run a torpedo heater for a bit to drive the chill out and bring the shop up to a comfortable level depending on my needs for that day. I don't have any experience with 8" so I wouldn't know what difference to expect.
Brad

Sorry, I thought it had an attic. Could it come in under an eve or sofit to avoid leaks? The point being that if the cold outside air is drawn horizontally, it needs to be drawn by the heater. If there is fall to the cold air there will be air flow coming out of the pipe and slightly feeding the fire. Agreed trying first without is better. My garage is a 6"system because that is what I triple wall piped for my previous wood stove. Right now I do not have outside air feeding the heater but I did build a solar collector to pre-warm the air some before it draws it into the building. Like you I built a pretty air tight building so it only leaks around doors and this helps considerably. There are some real good videos on utube about solar air warmers. One last thing. I didn't think of this earlier but you have to have a way to stop the air flow when it's near out. If you don't, the warm chimney will continue to draw and start working in reverse where it is drawing the heat out of the middle of the heater all night.
Brad

Brian. I hear what you are saying and you are close and that physics is the law and that for every cubic foot of air that goes out the chimney, a cubic foot of air is drawn into the structure.  I have two RMH and one is outside air fed and the second will be when I am done.  I built one to heat my 40 by 48 garage and one a year later for heat in my log home. I am now in my 6th and 7th season heating with them and tweaking them. Here's some of what I have learned. There are two types of triple wall. One is three layers of sheet metal with air in between and a vent for the out side gap. Back in the 70's with the birth of the air tight wood stove, it was found that this was great insulation and venting the outside gap didn't allow heat to collect. Drawing air in through here cooled the middle and outer layer enough to cause the inner layer to not draw as well. Then the second type was with the gap between the inner and middle layer with insulation. Now it was a much better combination even to the point of some stoves designed to draw the intake air through the middle and outer layer. For the RMH I do not recommend this. As we all learned cold air falls and warm air rises, wanting your cold air to com in from the ceiling where it is warm is great but it needs to be completely insulated so that the air STAYS cold and wants to fall. Mine is insulated to within the last two feet and by then it can't warm enough to fight the flow. The incoming air will expand when it burns and heats so you will not need as much incoming air.. I also would not put another hole through your roof for air inlet. I would consider an attic intake if the attic is properly vented. It wont leak. This works for me.
Brad

Hello all. I recently built and as of lest weekend am now running my second RMH. I have found, as most have, that cold start can be challenging. On my second build, I have incorporated a 1" iron pipe running into my chimney cleanout and then up my chimney to just under where the horizontal pipe from the stove enters the chimney. On this pipe I have mounted with a air mattress fan that, at the flip of the switch, blows a small fast stream of air up the chimney causing a venturi effect and drawing from the RMH. Once fire is started, up to a minute or so, the pipes are filled with warm air and the pump is turned off. Since there is no creosote anymore, I don't see any future problems. If this picture thing works you can see where the pipe enters the clean-out in the wall. The clean-out is sealed also so no leaking. I hope this can help someone.
Thanks,
Brad