sauna rocket stove progress

Mark Vander Meer wrote:
I’ve attached a photo of a two-room sauna we built last year.  Took 12 days start to finish;  raw logs to fire-up.  Had a sawmill on site, one logsmith who knew what he was doing and 4 men who know how to move logs and pound nails.  Took about 8000 board feet of logs and lumber.  This is fired with a good-sized steel wood burning stove, buried in several hundred pounds of rock. It takes about 3 hours to get to somewhere around 200 F.   

any chance you could post a photo of the interior, and the stove in particular?

Here are a few photos of the inside – taken immediately after construction.  Since that time we have straightened & strengthened the pipe;  replaced all the tin with brick, and place a triple layer of rock along the angled sides of the stove. This style of stove has a few sauna advantages.  The steel can get super hot and conducts heat well. The angled sides increase the residence time of poured water.    Steel also heats quicker after a pour and won’t crack like cast iron. The large capacity makes for fewer loadings – about 3 per sauna.  I left the top of the stove clear to accommodate a large pot of water.  This is our sole means for staying clean and such.  Fire wood and efficiency are not an issue; we have a huge, steady supply of wood.

Do you think a rocket mass heater can do the job?  I’ve not seen one in action. 

that looks real nice, Mark.  how many folks will fit in there?  and how long does it typically get used for when you fire it up?  do the rocks get real hot so that the water doesn't cool them off, or do you have to wait for them to heat back up after you splash them?  my guess is that you could run quite a few people through there without any problem if you've heated those rocks up for three hours.  very nice.

I do think a rocket heater will do the job.  my design isn't really a rocket mass heater, because there isn't much mass.  there will be maybe one hundred or two hundred pounds of rocks, but not even close to the ton+ that the mass heaters use.  I'm pretty sure that what I'm building will end up being a bit of overkill, but my design is based on what was available for free, and what I figure will last a long time.  I'm hoping it will take substantially less than three hours to get to 200 Fahrenheit.

and saving wood is definitely a concern for me.  I think we're growing enough wood that we'll be fine in the long run, but we're transitioning to wood from electric heat and I don't want to assume we'll have enough to burn through recklessly.

anyhow, made a little bit of progress.  sort of.  tore out the previous cob around the 8-inch pipe and replaced it with a more appropriate mix: coarser and sharper sand and no straw.  I also replaced the wire mesh I had used to span the gap with a brick split.  both changes per Maestro Denniston's suggestions.  you can't see the chips of brick I put over the gaps at the corners because they're buried under the cob.

(click to view the much larger original)

you can also see the high temperature paint with ceramic stuff in it that I painted on one side of the heat exchanger.  that side will go toward the wall, a wall which I would prefer not catch on fire.  I don't know that it will make any huge difference, but it was relatively cheap, and I can't imagine it will make things worse.

I'm a little embarrassed by my slow progress, but it's already saved me some trouble because of the good advice I've gotten in the mean time.

a little more progress today.  a couple of days ago I added perlite/clay insulation around the riser and capped it with some clay and sand that was on the sloppy side.  I hope that won't be a problem.



today I added the top of the burn tunnel and another course of clay bricks.



I also chickened out a few weeks ago and paid a shop to fabricate some duct for me instead of trying it myself.  I do not regret that choice.



some surfaces are painted with black stove paint and the ceramic additive to slow down heat transfer a little bit where I don't want it.

haven't yet worked out exactly how I'm going to seat the heat exchanger, so I'll probably be spending a fair amount of time staring at this thing in the near future.

did another course of clay brick yesterday.  might not be pretty, but it's progress.

Congratulations on the work so far! I've spent the winter wondering about my own sauna which needs a remont. I happened upon the board while sheltering from the cold, so you've given me some impetus to start planning ready for the spring build programme.

Is the plan to have a chimney sauna or are you going for more stones and a smoke saun? Several of my friends go on about the benefits of smoke saun and I've been thinking that the rocket stove would lend itself well to that style.

woodlander wrote:
Is the plan to have a chimney sauna or are you going for more stones and a smoke saun? Several of my friends go on about the benefits of smoke saun and I've been thinking that the rocket stove would lend itself well to that style.

I've thought about going the savusauna route, but this one puts the exhaust outside.  I could easily leave a cleanout open to let some exhaust into the sauna, though, which I might try.

project's been on hold for a little while.  hoping to get back to it real soon.

Have you settled on a place for the stones yet?

I've been puzzling it over and I'm in about three different minds for my own project.

I thought about heating them in a metal oven style device which would sit in a second box between which the hot gases would flow (a bit like the 3 barrel baking oven at aprovecho).

Then I thought that perhaps an oven type box which had the gases fed in directly might work. These are both a bit like the Russian system banya.

The question is whether the top of your combustion chimney is going to be hot enough to heat the stones to the required temperature fast enough? (like the Finnish system)

Have you had a tinker with it yet, before you connect up to a chimney?

haven't fired it up yet because it doesn't have a top on it yet.  haven't had much luck contacting the welder I'm hoping will make the top for me.  my working plan is to put the rocks on the top when I get it.  it'll be quarter-inch flat steel a little bit wider than the riser.  depending on what the welder says, I may have a little bit of a lip put around the perimeter to hold the rocks in.

if it isn't obvious yet, I started on this project without all the details worked out.  there have been some advantages and disadvantages to that approach.  I'm happy with it so far, but then, it hasn't actually worked yet.

so we've been using this stove for a few months now, and it's pretty satisfactory. because it doesn't have a long exhaust run and mass to strip heat, we're likely not as efficient as the full on RMH design. if I split wood real small and frequently reload the stove, it will get to about 240 Fahrenheit or a little more in around two hours. if I use a little bit bigger wood, it takes about three hours to get over 200 Fahrenheit. the main outer pipe heat exchanger gets up to around 800 degrees at the hottest point I've found when I'm really stoking it. so sitting near that is hot. if I'm not really pushing it, the pipe is usually around 5-600 degrees.

when it comes time to replace the wooden benches (lauteet), I'm thinking I'll probably do a renovation on the stove and add a good exhaust run and some mass, or maybe just a couple of bells made out of barrels on their sides. but that's years down the road.

more immediately, I'm wondering if welding some vertical fins to the heat exchange pipe to increase surface area would improve the performance of the stove. having read Ernie's thread about add-ons, I'm wondering if fins would create too much draw and cause a dirtier burn. it seems like it's burning pretty clean right now, but it just doesn't seem like it should take three hours to heat up a 6'x12' room, so I'm looking for ways to strip more heat out taking into account the limitations I've got at the moment. if it ends up drawing too much, would restricting the air into the top solve that problem?

also, it turns out that the pipes I used aren't .255" thick, they're .450" high carbon steel. pretty thick. grinding the ends was a pain in the ass.

went ahead and welded some fins onto the outer barrel. I think there are six at the moment. 1/8" gauge, 1.5" wide flat bar 30" long. they seem to be improving things.

previously, I've had some occasional smoke into the room. nothing serious, and probably more of an issue with the punky pine I was burning than with the stove. today, though, there was no smoke. it also seemed to heat up with less wood. I haven't measured, since my wood shed is full of many different species and I don't think a comparison would be very meaningful. but I used mostly the afore mentioned dry punky pine today, and mostly without splitting it smaller like I usually do. so I went longer between adding more wood, but the same 2.5 hours or so to get up to a good 200 Fahrenheit.

the temperature at the top of the barrel never got as hot as it has previously. just over 600 today, where it usually hits 750-800 for a while. I don't know if that was because of the fins dissipating heat to the room more quickly, or because I didn't stoke the fire with small wood like I usually do. not having the motivation to carefully isolate variables makes this all pretty subjective.

my guess was that this is working well because the 16-inch diameter pipe I used has a lot less surface area than the more common 55-gallon barrels with 24-inch diameter. but I've got 48 inches of pipe, and barrels are around 34.5 inches tall, so the difference is negligible. it is improving things, though.

I'll try to get some more photos up here at some point. I'm embarrassed to show my bad welding, though, and the cob is far from finished.

Sorry to dig up an old post, but I read through all the pages and getting to the end without seeing the final pictures was a little anti climatical Any progress Tel?

And we're thinking of pulling out our typical wood burning sauna and going Rocket Heater styles. I am a total newb with this stuff, but I would think a metal screen around the barrel filled with stones would look great and work well.

not much to report. it works pretty well, but there are certainly things I would do differently. it will probably be a year or so, but I'm planning a rebuild that should make it fit the space better. mostly, the heat exchanger needs more surface area, and some more mass would do it some good. it won't need near as much mass as a typical RMH installation, but it cools off in there more quickly than I would prefer after the fire goes out.

I never gave the cob any kind of finish, so it doesn't look great. by the time I got to that step, I was already planning a rebuild, so I lost motivation for making it look nice. life circumstances have kept me from using the sauna for the past few months, but I plan to start firing it up at least weekly again here before too long.

I don't have a camera with a flash anymore, so pictures aren't really feasible at the moment. sorry about that. still no climax for you.

Thanks Tel.

I am happy to hear it does the job well though.

Look forward to seeing what you come up with in the future.

Cheers,
Rob

wow.. that's a huge work. I watched the process because such things inspire me deeply. I don't have an opportunity to build my own real sauna now, but I made my dream (part of it, actually) come true by building a near infrared portable sauna, a few years ago. Now I use it in our bathroom, which is very small. I prop it up against the bathroom door once it’s closed. I then sit on my Squatty Potty and face the lamps. I rotate every 5 minutes or so in an effort to get my whole torso exposed. I sweat quite a bit just this way, but if I really want to sweat, I will also plug in a space heater and heat the bathroom up more so I can get more sweating in. I also do infrared with my CEs, but I use my single lamp unit and clamp it on the drawer next to the sink and lay underneath it..

resurrecting this old topic in preparation for a post-mortem. it isn't dead yet, but it's only a matter of time. we still use it regularly, and it still works well, but there are clear signs of deterioration. rather than try to fix it, I'm planning a complete rebuild. so maybe you could say it's in hospice, if you'll pardon the macabre metaphor.

over the ten years or so since I built this thing, it's probably been fired up around 300 times. because I was too lazy to address the issue, it always smoked back when there was strong wind from the south. and it took a bit longer than I would have preferred to heat up. and I didn't like the mess from bringing firewood into the sauna. otherwise, it's been great. certainly not the most flawless rocket in the world, but I don't feel too bad about it considering it was my first try.

the most obvious visible deterioration is in the first brick at the top of the burn tunnel, which split right in half. I was warned about this, but didn't have a great solution at the time, so I figured I would just deal with it. the brick is still in place, but the crack is getting wider with time. I noticed I could see flame behind it for the first time on Saturday, so it may be about to go completely. I can't imagine that my very amateurish cob helped things any.

I'm really curious about the parts I can't see, though. I bolted a top on the big pipe that's my bell so that I could clean it out, but I only ever opened it once a couple years after I built it. other than a rim of ash on top of the heat riser, there wasn't much to see in there. it's been ten years though, and I'm wondering what 300 fires have done to the steel.

not sure when I'll actually get around to tearing it down, but I've got a little bit more time for these things lately. maybe if there's any interest here, I'll be more motivated to get it done. I've recently been trying to track down materials for the replacement, but I've been doing that off-and-on since I built this one...

Hi Tel,    For every 100th stove build, there is probably only 1 that is shown being taken apart. There are so many things to learn from it that to not show a post-mortem would be a shame. Its this type of information that is seriously lacking with a lot of those you-tube rocket stoves that everyone thinks are great, but then you never hear from again. So I for one am very interested in your findings (the good, bad and the ugly). Pictures would be very nice as well if you can.

Gerry Parent wrote:Pictures would be very nice as well if you can.

should be doable. I've got a couple months of studying ahead of me that may interfere for a while, but I'll certainly document it when the time comes.