Funky Materials Concerns

I've been researching my project for a few months using Ianto Evans' book as a guide. I have a few questions about the materials I have assembled to build the rocket mass heater. Mostly about the used 8" stove pipe of various types of metals. I've been having trouble finding a steel pipe for the chimney heat riser for less than $50, so I'm considering using the 8" insulated stove pipe for that.
-Peter

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The used insulated pipe that I am considering using for the heat riser is 1" thick, but the gauge of the steel looks very thin... and not appropriate for heat riser. Is there a thread for triple wall pipe that was mentioned in the book? -Peter

If by heat riser you are refering to the piece inside the barrel, that should be fine. If you use it where it is exposed,inside the house, you might lose a little heat.

Thanks for your reply to my question.
Regarding triple wall stainless: "...it's durability is not known". That is the quote from the book. I'd like to hear from someone who has used it first hand, if possible.

By the way the reason that bricks aren't an option is that the combustion barrel is to be located (retrofit) inside of an existing fireplace, so there is limited space to work with.
-Peter

I've used triple wall for years and just installed a new chimney using it. It's durability is great. I've had some in place and working ,as we speak, for over 30years.

I'm pretty sure that what I've got is "double-wall" stainless stove pipe, not triple, because the insulation is only 1" thick. -Peter

Double wall is fine, you just want it 6' or more from flammable objects. Stainless will outlast rolled steel.

This is not for normal/ standard use with a stove.
I was hoping to use the insulated stovepipe as a heat riser inside of a combustion chamber for a Rocket Mass Heater. Temperatures will be much hotter than for a normal use of the stovepipe. It would basically be replacing a 1/4" thick steel 8" pipe, or masonry chimney, which is the recommended. -Peter

if its double wall its probably rock wool insulated. is this for the heat riser? how long do you intend your stove to last? Are you buying this stuff new?

Yes. this would be for the heat riser. And it needs to last 10 plus years, so I'm guessing that I'm just going to have to shell out the bucks and buy some 8" X 33" X 1/4" thick steel pipe .

The design also includes clean-out tee's for 3 of the 4 right angles for regular maintenance.

Again, thank you for your attention.
-Peter

Why not shell out less for fire brick and build a heat riser that will last you longer? half fire bricks are pretty cheap and the 1" rock wool insulation isnt to bad either.

hmm and while i am at it you might read the huge amount of information here at this forum. the search thing works OK.

Ernie, For inside the firechamber that should be very good.

Brick burn tunnel and heat riser; perlite around the burn tunnel and rock wool around the heat riser. it works just dandy.

I'll reconsider using the insulated pipe. Since I'll have to cut it to size I can check and make sure it's steel wool. A Brick riser would probably be too heavy for this project, because as i mentioned I've got a tricky maneuver. I'm installing the barrel in a fireplace space, which proves to have many challenges. I'll have to shove the barrel and assembled heat riser with insulation, etc. in together. Then block up the barrel while connecting the riser to the brick burn tunnel.

I'll definitely continue to read through the forum to see if something like this project has been posted before by someone else. -Peter

What size drum are you using for this install?

Peter gallo wrote:This is not for normal/ standard use with a stove.
I was hoping to use the insulated stovepipe as a heat riser inside of a combustion chamber for a Rocket Mass Heater. Temperatures will be much hotter than for a normal use of the stovepipe. It would basically be replacing a 1/4" thick steel 8" pipe, or masonry chimney, which is the recommended. -Peter

We have used triple-walled metalbestos-insulated chimney pipe for a heat riser in 2 stoves recently. To outside appearances, this is about 1" thick, there are usually screw-fittings on both ends that would nest into another similar section, and the outer walls are sealed together so you cannot tell what is inside. But it is pretty heavy. I would hope this is what you have, as it's a nice material to work with.

It makes a great demonstration material, but the question is, how long does it last?

In one case, it was the wrong size for the system, and the owner moved away, and the project was basically scrapped. No data.

In our other friend's house, at the right size for the system, it worked well for about 3 years. On inspection (by removing the barrel) the inner lining had warped from heat expansion, so there was a little folded kink in the metal poking inwards. You would think it would interfere with performance, but our friends had not noticed any serious changes. It is possible, as it had been stored outside, that the material simply had water trapped in the insulation. A small 'steam pressure' problem might be what vented out the hotter, more pliable inner lining.

You can drill a small hole in the outside to relieve this kind of pressure, if you aren't sure it has been kept dry.

If you can set up your system so that you can take the barrel off for annual maintenance, you can examine the inside for this kind of warping.

If it does warp, I would take a set of tinsnips and make a slit up the wrinkle, so that it can lie flat and expand past itself like ... one of those Kevlar bike-tire protectors, I hope that's a useful analogy, or a rolled-up newspaper. This should maintain better internal clearance. If you notice any discoloration or warping of the outside metal, it's time to invest in something more durable for high temperatures.

If you can find something else slim enough for the heat riser, like the half-size firebricks, kiln brick, or a ceramic chimney liner piece or two, I would be tempted to use the steel insulated pipe as your through-roof or through-wall connection. It's spendy stuff, seems a shame to subject it to an uncertain fate when it's so great for impressing the occasional in-law or inspector.

Our friends at Western Industrial Ceramics would be happy to sell you a sheet of 1" DuraBoard refractory insulation, not sure what they charge for cutting and shipping, but if you can go direct to a local industrial supplier we got a 4x2' sheet for under $50, and there are caulking materials that also handle high heats. The triple-wall stuff costs more like $200 to $300 for a 30" length, new.

-Erica

What kind of low temperature do you have in winter?

A step by step would be interesting to watch.

Here's the link to the thread I started awhile back. https://permies.com/t/11769/stoves/Rocket-Mass-Heater-Build-it

Lots of Photos, and I've got more recent ones coming soon. -Peter

PS
About the design for the RMH project: Except for the idea of "hiding" the barrel in the fireplace, with the burn tunnel positioned outside... it's a regular 8", 55 gal. barrel system as described in the book.

Winter temperatures in Albuquerque: Usually mild, sunny days (40's - 50's F) , with light freezes each night (20's-30's F). Lately the trend has been that once or twice a season, we'll get hideously cold snaps (-20 - 0 F !) that last a week or so. Not kidding. the RMH would theoretically replace the gas heater/blower in the 18' X 40' livingroom-kitchen space (except maybe during the week long the ice ages). One of the Mass walls would also be built along the outer bedroom wall, where my wife also keeps her office.

Thank you Erica for the detailed response!

Erica Wisner wrote:

Peter gallo wrote:This is not for normal/ standard use with a stove.
I was hoping to use the insulated stovepipe as a heat riser inside of a combustion chamber for a Rocket Mass Heater. Temperatures will be much hotter than for a normal use of the stovepipe. It would basically be replacing a 1/4" thick steel 8" pipe, or masonry chimney, which is the recommended. -Peter

We have used triple-walled metalbestos-insulated chimney pipe for a heat riser in 2 stoves recently. To outside appearances, this is about 1" thick, there are usually screw-fittings on both ends that would nest into another similar section, and the outer walls are sealed together so you cannot tell what is inside. But it is pretty heavy. I would hope this is what you have, as it's a nice material to work with.

It makes a great demonstration material, but the question is, how long does it last?

In one case, it was the wrong size for the system, and the owner moved away, and the project was basically scrapped. No data.

In our other friend's house, at the right size for the system, it worked well for about 3 years. On inspection (by removing the barrel) the inner lining had warped from heat expansion, so there was a little folded kink in the metal poking inwards. You would think it would interfere with performance, but our friends had not noticed any serious changes. It is possible, as it had been stored outside, that the material simply had water trapped in the insulation. A small 'steam pressure' problem might be what vented out the hotter, more pliable inner lining.

You can drill a small hole in the outside to relieve this kind of pressure, if you aren't sure it has been kept dry.

If you can set up your system so that you can take the barrel off for annual maintenance, you can examine the inside for this kind of warping.

If it does warp, I would take a set of tinsnips and make a slit up the wrinkle, so that it can lie flat and expand past itself like ... one of those Kevlar bike-tire protectors, I hope that's a useful analogy, or a rolled-up newspaper. This should maintain better internal clearance. If you notice any discoloration or warping of the outside metal, it's time to invest in something more durable for high temperatures.

If you can find something else slim enough for the heat riser, like the half-size firebricks, kiln brick, or a ceramic chimney liner piece or two, I would be tempted to use the steel insulated pipe as your through-roof or through-wall connection. It's spendy stuff, seems a shame to subject it to an uncertain fate when it's so great for impressing the occasional in-law or inspector.

Our friends at Western Industrial Ceramics would be happy to sell you a sheet of 1" DuraBoard refractory insulation, not sure what they charge for cutting and shipping, but if you can go direct to a local industrial supplier we got a 4x2' sheet for under $50, and there are caulking materials that also handle high heats. The triple-wall stuff costs more like $200 to $300 for a 30" length, new.

-Erica

I would very much like to see if the RMH will work out in thoes temps. We experience low temperatures, not often below 0, at both our places. Maybe building one outside to get an idea would be a good thing, for me that is. I'll be watching. How close are you to starting your stove?

Richard,
I'm ready to build at the end of the month.
I've seen "youtube" examples of RMH stoves with the burn tunnel outside, but i'm not sure about the temperature range there. there may be a few examples on the forum.

the patio area where the feeding tube is to be located may someday be part of an enclosed summer porch area/ winter wood storage, so that would increase the temperature a few degrees. -Peter

Well you all know my opinion on putting a firebox out side so i dont need to reiterate that. You can use a smaller barrel i20 lb grease can (jiffy lube) for your install with the manifold section made of a 55 gal drum. this would give you the space you want to work in without cause you heart attacks. that is why we put the steel and triple wall in the book. to give you more room and a smaller foot print. the 55 gal drum manifold is just tabbed so you can set the 120 lb grease can on it and seal it up with cob tape or stove cement (recommended) makes a neat job of it and gives you he volume needed for the fly ash. and you can put a clean-out as well as the exhaust ducting.

the only complicated part of the job is the indexing around the burn tunnel. a good indexing job will let you have a little bit of gap 1/4 to 1/8th and that will be sealed with the insulation and cob around the burn tunnel.

this would allow you much more space in the fireplace and let you have clean-outs that you can get to.

My mention of, my, building one outside was just to test/R&R.

The ranches have wood stoves. It would be beneficial to construct it properly and realize it can fulfill the heat needs in very cold areas.

The mention of -20, if it can work in this degree of cold, it can work anywhere. I could then consider installing one.

Best of luck to Peter, this is not a small undertaking.

richard valley wrote:My mention of, my, building one outside was just to test/R&R.

The ranches have wood stoves. It would be beneficial to construct it properly and realize it can fulfill the heat needs in very cold areas.

The mention of -20, if it can work in this degree of cold, it can work anywhere. I could then consider installing one.

Best of luck to Peter, this is not a small undertaking.

I believe that some folks on an Antarctic crew rotation already built one down there, and I think Ernie may have some anecdotes from Alaska too. "It can work anywhere" may be especially justified for cold locations. We easily get down in the 20's F here in Tonasket at 3500 feet elevation, and sometimes below 0 degrees F. Our heater works better the colder it gets outside. I admit I tend to stay home those days instead of going down to Ernie's dad's porch to check the thermometer. No point risking the one from my classroom set as it doesn't go that low.

It's actually warm outdoor temperatures, or a 'cold start' when the indoor temperature is colder than outdoors, that give a greater chance of draft problems.
On sites where occupants vacate the premises for weeks at a time in winter, or the ambient air temperatures during the heating system may be above 50 F,
we build conservatively (meaning shorter flue paths and a hotter chimney, 'conservative' of indoor air quality not of fuel), or add a draft 'bypass' or chimney-primer option for cold starts.

As long as you have appropriate exit solutions, cold outside air means hot exhaust has more lift, which tends to make any combustion device draft better.
(Appropriate exits can be a warm vertical chimney, insulated above roofline like code suggests;
and/or a horizontal downwind exhaust option (especially appropriate on longer systems where the temperatures may be below dewpoint/below ambient air temp. Greenhouse heaters often benefit from a horizontal exhaust, as the long, damp thermal mass can strip almost all the heat from the exhaust and leave it dribbling downward as a dew-dense fog.)
We sometimes suggest to make the cleanout accessible from outdoors, so it doubles as a horizontal exhaust / priming hole. But this encourages people to build the exit chimney outdoors too, where it gets cold, creating the very problem we were trying to mitigate. Indoor chimneys offer more benefits in terms of indoor heating, non-competition with home ventilation draft, and keeping the exhaust warm enough to draft upward.

For very short-term occupancy, like vacation cabins, we sometimes suggest a Rumford radiant fireplace, or adding a hefty brick hearth behind a woodstove to capture some of the heat and give some thermal mass benefit after the stove goes out. The learning curve, and the necessity for a caretaker to light the fire the day before in order to experience good results from thermal mass heating, can be prohibitive in a vacation rental/ rotating occupancy situation. Don't know if that's what you have on your ranches, Richard, or if they are occupied by long-term caretakers or owners.

Peter - It might be worth trying a Rumford retrofit while you have bricks on hand, before taking too many chunks out of the existing chimney. It can be a very quick fix for this winter's comfort, while you finalize the RMH configuration you want.

Erica. Thank you for your attention to detail and well thought out comments. They are inspiring!

In the discussion of appropriate exit solutions, there is mention of outdoor chimney vs. an indoor chimney. "Indoor" meaning that the fumes and all exit in the room? I thought I saw a thread subject on that, but never got to reading it.

I'm now considering placing the chimney primer on the outdoor section of (vertical) chimney, where it can double as a condensation drain with creosote trap. Design also includes some insulated pipe on the outdoor sections ending with the downward facing mounted elbow.

*To complicate this design question even further, I could theoretically "hide" the RMH exit chimney inside the existing masonry chimney, except that the existing flu is pretty small (3"X5"). But this would keep it warm and protect from draft. I believe there is an existing thread on this too.

Rumford Fireplace is not an option, currently. But here's an interesting link on the subject:
http://www.rumford.com/articleRumford.html
-Peter

Greetings, The ranches are occupied only as we migrate, taking with us some or all the animals with regard to the length of stay.

The mountain ranch is two story and is at 6800ft the stove there is large with a 4.5sqft fire box. During the 6mo of winter we will burn up to 4 cords. The Nevada ranch is at about 4300ft, the stove and chimney there I installed last year, when we secured it. That installation is not yet fully bricked or stoned.
When ether ranch stove is fired up the air temp heats quickly, however it takes several hours to heat the walls. Both stoves have fans.

That video on Rumford design was very interesting. We had a very well working fireplace at the big house when I was a youngster, we also had a wood stove. There were two chimneys and a place to install a stove in every proper room. But we only had one in the dinning room.

I'm waiting to see how yours comes out, how pleased you are and so forth. It could be just the thing for a green house.

Peter gallo wrote:Erica. Thank you for your attention to detail and well thought out comments. They are inspiring!

In the discussion of appropriate exit solutions, there is mention of outdoor chimney vs. an indoor chimney. "Indoor" meaning that the fumes and all exit in the room? I thought I saw a thread subject on that, but never got to reading it.

I'm now considering placing the chimney primer on the outdoor section of (vertical) chimney, where it can double as a condensation drain with creosote trap. Design also includes some insulated pipe on the outdoor sections ending with the downward facing mounted elbow.

*To complicate this design question even further, I could theoretically "hide" the RMH exit chimney inside the existing masonry chimney, except that the existing flu is pretty small (3"X5"). But this would keep it warm and protect from draft. I believe there is an existing thread on this too.
...
-Peter

Appreciate the kudos.

The chimney options all (should) exhaust to outdoors.

Outdoor chimney means: some people on a shack will run the chimney out a wall, and then extend a vertical section up outside the roof. I think this is usually in order to avoid the more expensive parts / leak problems with DIY parts for a through-roof chimney installation. Walls are usually thinner than ceiling-and-roof areas, too, so the amount of insulated stovepipe you need is shorter, and triple-wall gets spendy.
Problem is, these exterior vertical stacks sit out in the wind and can get quite cold, and that doesn't help the draft. Insulation will help somewhat, maintaining better draft, but you still have to 'prime' (warm) the chimney on cold days before it drafts right. Another popular option is to paint them black in hopes that the sun will warm them up for you. Optimistic, but not totally wacko.

An indoor chimney goes up through the roof, tends to exit near or above the ridgeline, and much more of the chimney is inside the house, keeping it warmer even before the stove/heater is lit. Chimneys that are mostly located inside the building, with only a short stack above the roof, tend to be warmer and easier to start. They also have fewer problems competing with the natural draft inside the house, which is up toward the roof vents.

3x5" is a pretty small flue, sounds like it would give too much drag for most RMH systems. 15" is comparable to the area of a 4" diameter pipe, and those definitely have drag problems and therefore draft/smokeback problems. Too much surface area compared to size.
Any possibility that there is a larger flue around this small one, that you could access as part of the original chimney?

-Erica