I'd rather pitch a tent indoors to reduce the amount of air that needs to get heated, and you can use candle lanterns to heat. I'd suspect you'd lose any gain in heat as soon as you opened the door to go outside in the heated rocks scenario.

No reason why that couldn't work. Of course you wouldn't use it to heat a large room, or expect to raise the temp to 75 degrees in cold weather, but it could certainly make a substantial difference in an enclosed space where you couldn't have a fire. In response to other posts, regular bricks and concrete block may crack when heated in fire, but they will not explode. The moisture bricks and concrete blocks absorb escapes easily without danger. However, some (but not all) river rocks and shale rock can explode. Several times I've seen such rocks liven up a sleepy group gathered around a campfire.

Makes you wonder why someone doesn't sell an inexpensive, flexible heat exchanger.

Maybe a radiator with a small electrical fan that goes on the inside of the house, connected to a coil and circulated with a small electric pump.

Just put the coil in your choice of heat; wood fire, charcoal fire, propane BBQ, small alcohol burner, etc. and turn on the pump.

Extra credit uses a user placeable solar cell and battery set to keep the motor(s) going.

A small version of this could be used for vehicle heating.

-john

For extra special extra credit, replace the solar panel and battery with a Sterling Engine.

Just to make it fun, use a fuel cell. You sit inside enjoying the heat and a toddy, blow into a tube from time to time, the alcohol in you powers the cell, which powers your fan. More toddy's, more heat...

You get extra credit for "dual use". <img src="/images/graemlins/cool.gif" alt="" />

I have to tell you this works great. I know some of you doubt this but allow me to point out this is the same process the native ammericans have used to heat up sweat lodges for hundreds of years.
Obviously the larger the area you are heating the more rocks you will need, but I can tell you from personal experience that just a couple of rocks the size of two fists was capable of heating an area the sixe of a large 5-6 person dome tent.
A load about like what was originaly described[a couple of gallons] is what is normally used for such a sweat lodge, and will heat it up hotter than the average sauna by a great bit. Heating a small room would be no problem.

Obviously there is some variation with the type of rock used, and the amount of area to be heated, but the process will work. The ammount of wood involved is equal to a largish camp fire/smallish bonfier and it takes an hour or two to heat the rocks up so the wood used is an investment, but you would use more in an open fireplace overnight.

Just my 2 cents worth, but I would not have belived a few rocks could have heated an area and retained the heat for so long had I not seen it.

Interesting info. I had not even thought of sweat lodges (HUA on my part). About how long will a heated rock produce heat before it has to be tossed in the fire again???

That really is a physics question. <img src="/images/graemlins/smile.gif" alt="" /> Size and mass rule, but the type of rock has some affect as well.
A dense lava rock about the size of 2 fist side by side will hold the heat to the point you dont want to pick it up by hand for several hours.
Some rocks you can heat over and over, I have lava rocks I have heated around 20-50 times. The white not-quite-limestone in south dakota crumbles after one heating. but even it will stay hot for hours.

> I have to tell you this works great. I know some of you doubt this
> but allow me to point out this is the same process the native
> ammericans have used to heat up sweat lodges for hundreds of years.
> Obviously the larger the area you are heating the more rocks you
> will need, but I can tell you from personal experience that just a
> couple of rocks the size of two fists was capable of heating an
> area the sixe of a large 5-6 person dome tent.

Okay, I'm willing to reconsider. Tell me how many people are involved in setting up the fire, what they used to burn for the fire, how big is the fire.

How long do they keep exchanging rocks and how many days does a sweat lodge last?