Jim Fritz

Rick,

I'm actually looking at that. I'm on my third stove in twice as many weeks and all along I've been messing with ways to collect core temperatures for a microcontroller. I've found you can tune the combustion based on the draw and completely compensate for the differences between kiln dried hardwood and damp green wood chips. The stove design is refining itself, but I've already melted through a handful of K type thermocouples. However, with each failed attempt I've learned one more way not to do it and I'm currently on day five with my current configuration. I am running an 8 inch fan on a 5 inch system. Actually there are two in an exhaust plenum, read redundancy. As for the smoke back issues, I've found by preheating the exhaust my sealed chamber with an exterior intake is working quite well.

Oh, and as for those redundant fans. It is quite scary if you turn them both on at the same time at full RPMs. I mean the sound is amazing, though realizing your core just went molten is not so cool. It is however quite scary and exciting.

Right now I'm on the lookout for a used Testo so I can create some hard data to backup my work. The first one I bought wouldn't allow me to log the data, but on the plus side I turned around and sold it to an HVAC guy at a profit.

We all employ multiple smoke and CO detectors, no? I'm also not sure how many people who are capable of fabricating a rocket stove/heater would call a repairman to replace a furnace blower.

However, fair enough, an alarm for a failed blower.

I realize fans and electricity fail. Everything fails. I'm looking at ways to overcome the limits of the mass run length as well as extracting all of the heat. And, I'm looking for design reasons not to use an active exhaust. The fan may fail Isn't enough of a reason not to use it. If it were no one would be using forced air furnaces. Given nearly complete combustion and the ability to deal with condensation a quality fan costing not much more than 30 dollars should give decades of service. And the additional recovered heat would rapidly make up for the purchase price and the minor use of electricity, right?

Why not remove 100% or as near to it as possible and drive the exhaust with a fan? If the mass was designed to deal with condensation is there any reason not to do it? We're talking about very low energy usage something like 50-100 watts for an efficient fan motor with a good blade design. It seems more efficient as that last 50-80 degrees needed to drive a chimney represents a greater energy loss than would be needed to drive the stove/heater.

Max, I'll think about how I could go about casting an inner refractory mortar only piece and then a clay and vermiculite insulating layer around it. I see what your saying, basically creating a hotface and putting a cast insulative layer around it.

As for your stove, I had read all about before. I love those stove and have a giant in storage among e everything else that I hope to use someday in someway. I really wish we could get those refractory flue pieces over here. All we have are clay flues which don't much like the serious heat the rockets generate. My stoves will take them out, I'd worry about what a real heater would do.

Thank you for the suggestion about the hotface. Would you think an inch of the refractory mortar surrounded by 2 to 3 inches of insulation will work well?

Does anyone have anything to say about my insulation core/heat riser recipe. I'm hoping a healthy percentage of refractory mortar to clay ratio will help with shrinkage, crumbling, and wear. It is worth 60% of project cost to add from what I've read, is the dry mortar material not as robust as the wet castable refractory in the buckets? Is 8 parts vermiculite unnecessarily high? I want it insulative, but is that too high of a proportion as to make it too crumbly?

Thank you, Satamax. The one thread I had read. I have an old stove sort of like that, that I love. But I can't take up that much space in this version of the tiny house. I will scour the other thread this afternoon. I appreciate it.

Hmm... I just found a couple hundred pounds of mason's sand. My workshop is filled with many wonderful surprises, read I'm a but of a picker and a pack rat. LOL Anyway, could/should I add that to the refractory, maybe 1-2 parts? To help with the shrinkage and to increase it's ability to withstand abrasion in the feed tube.

I am just about to cast the burn chamber and heat riser for a 5 inch CSA rocket stove/heater. It is going into a reasonably well insulated 128 square foot/896 cubic foot house. Yes, tiny is the word of the day. Anyway, I am looking at 2 inches of refractory around the burn tunnel and feed tube and 3 inches around the heat riser. I have a feed tube length of 7 inches, a burn tunnel length of 14 inches and a heat riser of 28 inches. These measurements being from edge to edge. If using Peterberg's centerline to centerline measurement method they would 4.5-9-25.5 respectively. I am planning to use 1 part refractory mortar, 2 parts ball clay (it was free and my profesional potter friend said it could be fired to a cone 12 safely), and 8 parts vermiculite. I would appreciate any comments anyone has. I did model this configuration sans the insulation and it burnt and drew well, though my experience is mostly with stoves and not heaters. I do plan to add some mass to retain some of the heat though space will dictate how much. Right now I would appreciate some heating during the burn, but I am mostly after a good stove to cook on. Well, appreciate is a weak word, I would love the heat. I'm getting a little tired of running the 1500 watt electric heater which is currently heating the space. By the way this is virtually my first post here and what I consider my first real rocket mass heater build. Thank you in advance for your comments.

450-500 sustained sounds right to me from everything I've been reading and I've been reading a lot. Probably 200 hours in the last few weeks. With that said I should say I've only built stoves up till now, no heaters. However, I'm just about to assemble my first proper rocket heater tonight. Temporarily to test my odd design. If it draws OK I'll be finishing it off tomorrow. I hope it works, knock on wood. I know how everyone likes to caution to build one to the book first, but what fun is that. LOL