We want to design a sauna using a normal hot water heater as the sole heat source.

We have a super-insulated tank that requires n BTU/hr. to maintain an interior temp of 150deg.F (at an arbitrary but defined level in the tank) within a room at an ambient temp of 60deg.F.

The idea is to simply expand the tank's insulating envelope to 7' X 7' X 7' &, w/o increasing the energy requirements by more than, say, 1 BTU/hr. to heat the room to approximately 150degF.

We are toying with R-65 walls & perhaps R-100 ceiling, but are not sure about the floor. Although we're playing with some heat transfer/loss formulae, we'd like the proper formulae & considerations to use here. We're happy to switch to metric, if you like.

Lets start with a question, what do you think is the max. temp setting for any water heater?

Hi,

Thanks for getting back to me, I think. Looking at your question in the best possible light I would respond that we live back in the VT woods, heat our house & water with wood & solar, cook with wood, have a composting toilet & the house, it's plumbing, electrical & HVAC, is designed & installed by myself with help from others. I majored in physics & biology & am a computer systems engineer with 45 yrs. Experience in the field. All that by way of saying that I'm an opinionated old bastard sometimes thought by others to be pig-headed. However, my wife & I are very comfortable here - except we crave a sauna. (Our hot tub is a 150gal. Plastic stock tank... )

Last year I built a proof-of-concept "sauna" box hoist-able by block & tackle that collected & trapped heat from a downstairs woodstove (it had manifolded air passages whose outputs I gathered up sent up an auto exhaust pipe with a couple of PC box fans - which also allowed for water to be squirted down it for steam) & had a bench setting w/in. We heated it, lifted it, got onto the bench, lowered it - no leaky door required. However, I learned the hard way how important R value is when asking to maintain such a steep temp gradient.

Our solar & masonry stove hot water supply is essentially inexhaustible. I control all pressures & temps & relief valves, etc. Not asking for OSHA-approved advice. No bldg. codes at all out here. But I'm leary of sinking $1600 of EPS into this thing w/o at least asking for some guidance.

Back to your question: 110 - 160, avg. 140. I use a mixing valve on mine for safety.

Regards, Gerg (aka Greg)

Ok sounds like you know your way around things. I asked because residential water heaters don't go over 120 degrees but you are planning on using exhaust gasses. Keep us informed as this project moves forward, I was going to give you the code/safety angle but ypou are well into cobbling concept projects

Do you, or someone else, have anything to offer re: BTU heat loss through the walls given those temp gradients? Or, perhaps, the best floor treatment that would allow for rinsing it out w/o losing too much heat?

I'm leaning toward EPS because its manufacture isn't so harmful & its disposal is relatively benign, but am open to other ideas...

Thanks, Gerg

I am not very familiar with your climate, Chicago is bad enough for me. I think you best band for the buck is this stuff http://www.dow.com/PublishedLiterature/dh_003c/0901b8038003c56f.pdf?filepath=styrofoam/pdfs/noreg/716-00150.pdf&fromPage=GetDoc You can layer it as thick as you want, even on the floor, it is moisture resistant and will not rot.