Wheaton Labs Rocket Sauna Build

Josiah and I are discussing our design for a skiddable rocket sauna at Wheaton Labs.

It will be a dry sauna, approximately 4 feet by 6 feet interior dimensions (very small, we know, but we want to build the first one quickly and cheaply, mostly for our personal use at the Abbey, and then iterate our way to bigger and better things), skiddable, and made from natural materials (insofar as possible). We are trying to get a design more or less finalized and priced out, but are being held up by our lack of a good heater/stove design. Neither of us have built a rocket heater before, and we need to do more research before we can come up with intelligent designs, but we're hoping that getting some input from the permies community can speed up our learning curve.

For the stove design, we need something quite small so that it does not take up too much floor space in our tiny sauna. However, we would be willing to add a foot or two to the 4'x6' dimensions we're thinking of if the stove design requires it. We definitely want a J-tube style, not a batch box. Since we want the space to heat up quickly for our saunas, but not necessarily to retain the heat for a long time, we do not want much if any mass in our heater. We have considered something like a cottage rocket, or a pocket rocket like the Minnie Mouse heater in the Love Shack. One issue with the cottage rocket is that it does not seem to draw very well, possibly because it does not have a full-sized heat riser (or so I have heard--I haven't actually used that one). Apparently the Minnie Mouse is also a little finicky. So we would like to improve on the "pocket rocket" as it exists, if possible.

One possible design involves a 4- or 5-inch J-tube and a 30 gallon stratification chamber (barrel) with a secondary stratification chamber (barrel) in line to pull more heat out before the exhaust exits the system.

The two barrels could be stacked, but that would make heating bath water on top of them slightly more difficult due to the height.

As far as the structure itself, we are thinking of using 2x6 stud walls to save weight and for ease of insulating.

For insulation, we are considering slip straw, wool, rice hulls, and any other natural materials we can think of. We want something that will not add so much weight that the structure is no longer really skiddable, and that will not rapidly mold or degrade.

Any input on the sauna and especially the stove design would be appreciated! We will be documenting the project here as we go along.

Thanks!

Hi Jen;  
Let me make a few suggestions.
First stay with a 6" J tube (they work better) and easier to build.  Paul may make you a good deal on insulated firebricks...
Consider using a walker style 2 barrel bench (heats fast, nice to sit on), A 30 gallon or a 55 gallon barrel will heat you up fast
Next about your building)  Its a sauna, with a rocket stove... Its gona get plenty hot!  Why insulate at all ?  (maybe the roof) also use 2x4 if your not insulating , its cheaper.  Use a  steep pitch on your roof so snow buildup isn't a problem.
If it's a skidable building then build the floor extra stout and use diagonal braces on the walls.  They like to tweak when moved.

Hope this helps ! Have fun with your build!

What Thomas said. +2 on diagonal bracing. Diagonal brace the floor and "ceiling" also.

Consider "air in" and "air out" (the flue). Not complicated, but I think you don't want to just leave the HVAC to the cracks in the floor...

I'd want to insulate the floor for sure. Hate cold feet.

Close the ceiling, seal it. Keep it low. Keep the "attic" empty, even open. An "open" attic helps keep the roof cold which reduces melting of any snow up there and having to deal with run off.

You're probably going to get some melt water somewhere anyway - which will then freeze and provide a nice slick surface. Maybe keep in mind something for safe, dry, convenient foot passage in and out.

IMHO, build it bigger. Makes, I think, for better ergonomics. Doesn't cost much more, doesn't weigh much more, doesn't take much more work to move, etc etc. Well, unless you're going to move it with human muscle. But still. The heaviest thing may be your heat source.

Not sure I understand "dry sauna". Is this _not_ going to have a dipper and water to splash onto something hot and make steam?

What about a heater similar to John's in This Thread?  It kind of looks like a rocket mass heater but without the mass.

Would there be an advantage to having the firebox outside so that you can start it up on your way into the Abbey at the end of the day (without tromping mud into it).  Then change into your sauna suit and let the sauna heat up for a bit before running out there?  Maybe it would save space...

Sounds like you want to heat bath water on it as well.  What other functions are you hoping to integrate?  Will it truly be dry inside?  If so, I'm guessing mold won't be too much of an issue.

If there's a chance you'll heat yourselves out of it, you may want to think about how to control the temperature.  The smaller the sauna, the harder the temp will be to control.  Less or no insulation may actually help with that.  Or consider building it without insulation and trying it and then add insulation if you find you need it.

Consider that at this size range, it may be quite practical to pick the whole thing up with the tractor forks, and either carry it that way, or place it on a trailer for longer moves.

Requires a strong floor in a somewhat different way than skidding, but if kept in mind shouldn't add much cost or hassle.

I have done this with a 50hp tractor and a 6x8 shed, heavily built. It was quite interesting as the shed is 10' tall, quite tippy.. but the weight was no problem.

An 8x10 pig shelter, only 4' tall, was much easier.

Key in both cases was 3300lb ratchet straps to secure the shed to the backplate of the forks.



Small is quick, but temp control might be easier wth a bit more space..

I will second the others who are suggesting a slightly bigger footprint. You usually want two rows of seats (low and high), 12-18" in depth and about 24" of walking space in the floor. At 4' you'll only get a 12" wide walkway, which would be a bummer. One of the problems with saunas is you have to put a stove in there, and no one wants to be squeezing by a red-hot stove. So it ends up taking 3-4 "seats" worth of space. Of course this all depends on the shape of your stove! So I think it's good that you're focusing on that end. Figure out how much space the stove/barrels are going to take up and you can play with the footprint to work around it. I think I'd also agree that insulation is less important with an occasional-use sauna (as opposed to one inside a gym/spa). You're kinda designing a structure for extremes, and insulation helps combat extremes. You're probably better off optimizing for air/vapor sealing than R-Value.

I have experienced Native American inspired sweat lodges that got the job done. They didn't have a fire in them, just a small pile of really hot stones that had been heated on a bed of coals outside the lodge.

What Kyle says resonates true with my sauna building experience.

What i gathered is that you need to have the air flow going into the sauna from the bottom close to the place where the stove is to get fresh oxygen in and a hole up high to the outside world so heated air can leave as well to guarantee enough air flow (oxygen) for the sauna-takers. When battling the heat you don't want to feel that you can't breath on top. The blast of heat in a small space is sufficient to get temperatures to boiling point. That is with a regular sauna wood stove, the power of a rocket stove is much bigger and will heat it up superfast. People manage to build a sauna in a tent even. Following that line of thinking you could argue no insulation at all.
My experience is that some people, mostly females prefer less hot temperatures so they go in at the beginning in a normal set up and the men join a bit later. With a rocket stove it gets hot really quick, and then you lose your heat rapidly if not insulated at all. Then you have to light another fire, which is quite messy when you're wet and sweaty and want to relax. It's something to take into consideration. A normal sauna stove is quite a bulky metal thing and has the lava rocks on top, which heat as well and serve as a thermal mass. Lovely to throw water on there infused with some eucalypthus or a hydrosol of pine tree.
Nothing gets you more thoroughly clean then a sauna. All the pores open and gush out sweat and dirt. I have a shower adjacent , the cold water makes me resistant against the heat for a bit longer and when heated up it makes me resistant for a bit against the cold water. A lake would even be better a place where you can take a dip in.
I had a sauna party with many people and a kid almost touched the stove so build a little light weight safety rack. Heavier at bottom , because of the log base, light hazel standing wood and tied together by willow.

Air inlet next to stove is the door is 3 inch short.

Hugo Morvan wrote:What Kyle says resonates true with my sauna building experience.

What i gathered is that you need to have the air flow going into the sauna from the bottom close to the place where the stove is to get fresh oxygen in and a hole up high to the outside world so heated air can leave as well to guarantee enough air flow (oxygen) for the sauna-takers. When battling the heat you don't want to feel that you can't breath on top. The blast of heat in a small space is sufficient to get temperatures to boiling point. That is with a regular sauna wood stove, the power of a rocket stove is much bigger and will heat it up superfast. People manage to build a sauna in a tent even. Following that line of thinking you could argue no insulation at all.
My experience is that some people, mostly females prefer less hot temperatures so they go in at the beginning in a normal set up and the men join a bit later. With a rocket stove it gets hot really quick, and then you lose your heat rapidly if not insulated at all. Then you have to light another fire, which is quite messy when you're wet and sweaty and want to relax. It's something to take into consideration. A normal sauna stove is quite a bulky metal thing and has the lava rocks on top, which heat as well and serve as a thermal mass. Lovely to throw water on there infused with some eucalypthus or a hydrosol of pine tree.
Nothing gets you more thoroughly clean then a sauna. All the pores open and gush out sweat and dirt. I have a shower adjacent , the cold water makes me resistant against the heat for a bit longer and when heated up it makes me resistant for a bit against the cold water. A lake would even be better a place where you can take a dip in.
I had a sauna party with many people and a kid almost touched the stove so build a little light weight safety rack. Heavier at bottom , because of the log base, light hazel standing wood and tied together by willow.

Air inlet next to stove is the door is 3 inch short.

I was having a hard time picturing the upsides to a rocket in a sauna, if there is not much mass..

This seems to back that up..

Rockets are super neat. But is this a good place for one?

Oh my goodness; Tiny split wood dropped in a J tube rmh , while having a sweat ?   Couldn't get much easier.  Rather fun really. That stove won't go out until they want it to.
If they go with the walker half barrel bench system there will be some mass as well.

I’m only saying what i know about my sauna and saunas in general.I’m not implying it can’t be done with a rocket stove at all.
Go for it! Godspeed!

$0.02

A friend swears by the sauna.  A minimum size is 1 inch larger than you are with a head hole to poke your head out of.


One of the Nifty things about the Finish style sauna's is they were built first in most long term camps.    With this there was always a refuge for getting warm and clean ( and delivering children ).


I'd council the size be increased so that someone could use it as a sleeping space in a pinch.  So a bench of at least 6 1/2  ft x 30 in  or so.


With a bench high and a bench low, this results in a 4 or so person sauna with space.


With a little bit more space it might also serve as a winter time clothes dryer.   ( just add clothes lines or drying racks )  


I'd second the safety fence around the burning bits.

Good luck!

Just to clarify, the cottage rocket in the shop had a very strong draw before we added the second barrel.

Fred--thanks, I didn't realize that. Did it have a different chimney previously or were other alterations made? What is it about the second barrel that messed things up, do you know?

By extracting more heat from the exhaust,  it is less eager to go up the chimney.  We didn't change the chimney at all, except for putting the second barrel and all of that resistance in the way. So, more heat was going out of the building = less efficient.

Here's a possibly silly idea that I posted elsewhere.  What about making the heater be on a small trailer so you can heat the sauna with it one day, and then move it and heat another building another day?  Here's more detail:

https://permies.com/t/131988/Portable-Rocket-Space-Heater

Fred, thanks for the info! Much appreciated.

Mike, I have no idea if the idea is silly or not, but it certainly sounds convenient! I will talk it over with folks and see what we come up with.

Plus inner one on bigger, even for the first one.  Distance from the heater is a temperature control.  Plus big enough to do basic yoga stretches inside is wonderful.

Put a damper or sliding door on the upper vent for a second temperature control.

So here's where we're at on the sauna heater:

Full sized wood feed and heat riser. So not a cottage rocket/pocket rocket.
Bigger sauna (but still not too big). Maybe 5' x 8'. Also relatively tall. 8 or 9 feet.
One barrel oriented vertically (like normal).
Maybe two barrels oriented horizontally under the benches, forming a stratification chamber.
4" vertical exhaust pipe which pulls from the bottom of the stratification chamber and is located very near the first (vertical) barrel, to warm it and improve draw (which has been a problem in the past with multiple-barrel systems).