Kathie Thomas

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since Mar 29, 2017
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Recent posts by Kathie Thomas

My oh My love this concept... I see its been a couple of years since you did this any follow ups ?  I have a fireplace like this and sure could use the plans materials you have thus far created to use in later work up on this one.    

Richard Jarel wrote:Hello,

Let me first apologize in advance for such a long post. This system is far from ordinary,” breaks all the rules”, and is not shared as a completed project, but rather a proof of concept prototype.

I wanted to share here in hopes of getting some critique, especially about low burn temps, ash, creosote, safety etc… as well as getting ideas for further development. We’ve been running this system for just over a week now, burning less than 1 square foot of wood per 24 hour period and maintaining our indoor temps between 70 and 73 degrees, (It’s below 30 outside here this morning.)

I’ve spent many months reading through many websites, watching countless you tube videos (the good, the bad and the ugly), and reading through several books, including “The Book”… (Still reading.)

Brief Background: 25+ years as a professional designer and prototype developer with projects ranging from toys for Mattel & Hasbro, to deep sea diving equipment for the Discovery Channel, wind tunnel models for Northrop/Grumman, (background in aerodynamics), UAV design, designing & building three human carrying ultralight aircraft, two world land speed record vehicles and much more.

A few months ago, I built a 34” X 75” “zero pass” style, aluminum screen, solar heater and when the sun is out, it brings our indoor temps up to 70 degrees for only 21 watts (computer fan), while outdoor temps are 25. This doesn’t happen though when it’s super cloudy or raining or at night, so I decided to try and design a system using our existing fireplace a rocket stove.

My priorities included not having it be “visually or spatially invasive” to our living room (I did not want to use a large “barrel”!). I wanted a radiating heater as well as “some” mass heat storage

I am very aware of the issues using metal (especially using stove pipe for my burn chamber!), I’ve read countless threads focused on this very subject and have seen the photos of corroded Stainless risers and burn tubes. I plan to “evolve” this concept into a high-temp refractory final version, so please, any “positive input” is desirable, but I’ve read so many “wrist slapping” posts provided to those who have gone the “metal route”… This is a functioning, “proof of concept” model only, operating at lower temps (1,000 degrees at the burn tube)

I do some amazing mold work and plan to re-visit this concept using high temp refractory mixes to replace components in this system. I’m already experimenting with high temp silicone poured into platinum based silicone molds to create true sealing gaskets between refractory and metal components that won’t leak, will hold up to temps and contact and expand without cracking refractory components.

Regarding safety and operating this first generation rocket stove heater in our home: Before moving up to Oregon, I was a firefighter for LA County (experienced too many needless tragedies!). I purchased two digital Carbon Monoxide alarms just for this project (different brands and models in case there was a “defect,” in one, I didn’t want to discover the same defect in my ”back up” alarm). I am obsessive about safety, which is also an important reason why I’m sharing this here, looking for feedback and more information to work with.

I built and tested this basic design in my shop and was surprised by its performance!!! Especially while breaking so many “rules,” I was really surprised!

I built this “proof of concept prototype” design using 6” black stovepipe in less than one week. (I already have LOTS of improvements and changes I want to make and I’m thinking of many others as part of the development process.) It cost me under $400 for everything and that included all the “incidentals” (firebricks, stainless screws and fittings), and also included about $100 for two digital Carbon Monoxide alarms (We already had smoke alarms in every room of the house.) These alarms were “extra”: One in the living room closer to the insert than recommended (I’m fine with false alarms, especially while just starting out with this prototype, but so far, nothing.), the second, is just outside our bedroom.

Changes I already plan to make include building an angle iron frame for the current loose, vertical stacks of firebricks to prevent them from tipping over, screwing that frame into the existing white masonry ASAP. I fabricated aluminum standoffs, screwed into the white original fireplace bricks, and used SS hose clamps to secure the vertical pipes a few inches away from the existing white masonry. They are very secure!

I’m also researching creating cast j-tube systems and other components, possibly eliminating the bricks. This will probably raise over all temps through the system allowing me to burn hotter and cleaner but I have to see how that would effect heat transfer (radiant and mass), to our interior. I’ll be testing any high temp cast components/systems outside first!) Right now, indoor temps remain constant for about 3-4 hours after the last burn goes out… I’d like a little more (5 to 7 hrs?).

I’ll also be building a heat shield (perforated stainless sheet metal supported by angle iron frame), over this or any future horizontal radiating pipe, if it stays in the final system… I do like the instant, radiating heat, but I’ve already burned my forearm when I tried to support myself getting up while feeding the stove and operating the lower damper (I wasn’t thinking!)…. Nasty 2nd degree burn across my forearm!

I’ll be adding a second ash clean out at the bottom of the right side down tube for this temporary build… molded/cast, later on.

Right now, I’m burning a mix of hardwood (Madrone and Walnut, combined with pallet pine). Removing the side Tee cap where the bottom side tube damper is located, I sweep out 1 to 1-½ cup of super fine ash/dust before lighting it up each morning. (Last night, we burned primarily Madrone and I swept out even less than that.) After one week of using this system. I removed the top, cross tube to check for ash build up and emptied about 1-2 cups of fine powdery ash. I need to be able to burn at higher temperatures to correct this.

NOTE: I have NEVER experienced ANY smoke, blowback, smoky smell, or flames creeping up the feed tube! Ever! Flames are straight and horizontal going toward the riser.

After a week of use, I’m getting the following temps: (These are averages, depending on wood type, intensity and duration of burn.)

Bottom of Tee at burn area: 780 to 1,000 degrees I doubt it’s getting over 1,200 but my IR thermometer just reads “high” after 1,000, which I sometimes get… I’d say the average burn tube temp is about 750 to 950.

First riser (on left), 200 to 400 (Average is about 300)

Cross tube: 200-300 (I have a separate temp sensor that shows that the wood mantle (above the cross tube) never gets above 110 degrees.)

Down tube (on right): 200- 250

Additional ducting tubes towards back of fireplace: (175- 250)

Last vertical exit duct into existing chimney: 140 – 200

Height of vertical riser (from floor in burn tube to top of cross tube/first elbow) is 42”. Length of cross tube (along top) is 48”. Height of feed tube (Top opening to bottom of 6” Tee), is 18”.

I’d say draft is excellent. I get straight, horizontal flames like a jet engine afterburner and we can hear a nice “rocket roar” (Well maybe not a loud roar, but we can hear it from across the room)… Nice comforting sound for us!

All ducting is new black stovepipe. After I cut and fit the entire system together, I disassembled everything and baked all the components in our BBQ to about 800 degrees (Checked with IR thermometer). After the black stove pipe paint stopped “fuming”, I baked the parts some more until the black color turned to a flat, dark gray, then I baked it for at least 30 minutes more for extra measure. We’ve had zero paint fumes.

Our original fireplace damper was wide and narrow, so narrow, that I could not feed the 6” stovepipe through it. I used a piece of “backer-board” and created a “ceiling/roof” inside the fireplace, just a little lower than the original damper to seal it up. I cut it to be fairly tight fitting (1/8” to ¼” gaps to help bring it in and place it). I used 1” angle to support its weight and then sealed the gaps with 600 degree Hi-Temp silicone. The exit ducting has its’ own hole to extend through the backer board and the edges between the exit ducting and backer board were sealed using more hi temp silicone.

A great feature is that I can shut off our central heat system and leave the fan blowing. Its’ air intake is about 12’ from the fireplace and with a small fan (Seen just to the left of the top elbow), blowing air across the top tube towards our central heating air intake, our central air system sucks up the heat and distributes it evenly throughout the house! We’re averaging about 70-73 degrees inside, evenly and everywhere!

I still have a lot of general questions about acceptable amounts of ash, possibilities of leaking duct/elbow joints (So far, I’ve found no leaks (which goes against my prototype development and firefighting experience, but I’m still testing!), exit duct temps and concerns about Creosote build up and Carbon Monoxide production (especially burning this system, at much lower than the “classic” firebrick temps/designs). (I’d also like to get a Co monitor that measures levels well below alarm levels.)

I have been told and read many times that using metal is an absolute “No-No”… My expectations for this system as is, include replacing “at least”, the bottom “Tee” through the first two elbows and the riser tube within a year or two (at best)… I hope to design/develop a refractory molded replacement design before then.

With what I’m experiencing, I’m searching for a system design that produces radiant heat and stores heat in mass collectors. I want to go with “proper” high-temp refractory components for the burn chamber and a proper, insulated riser, but I’m concerned that any metal radiant tube across the top will give off too much heat.

My ultimate goals include keeping the visual design as intact as possible (aesthetics and not bringing anything into our living room like a bench or a barrel), burning at hotter, cleaner temps without elevating the heat in our living room too much, being able to store “some” heat (enough to last for at least a few hours, maybe up to 6 hours), and to insure safe operation.

I’m the type of person that thinks “outside the box” and willing to do the work, take the time to experiment, make mistakes (outside!), rebuild and do what it takes to reach a goal. (It’s what I do for a living…. And… the actual designing and building is what I live for as a favorite pass-time.)

Your feedback is very welcome!

Thank you!


2 years ago