Maybe this was too obvious for me to think of, because when I read it, I thought, "WOW! What a clever idea!"

I am currently reading Tom Brown's Field Guide to City and Suburban Survival (1984). His suggestion for safe indoor heat without danger of carbon monoxide or oxygen depletion:

He says even if you can't build a fire indoors, you can build one outdoors and bring the heat in. Build a roaring fire outdoors and drop several large rocks, bricks or chunks of concrete into it until they are very hot. Then carefully shovel them into a large stainless steel or other non-coated cooking pot (don't use aluminum, galvanized or painted containers).

Carry the pot indoors, maybe running a broom stick through the handle and having a person at each end. Place the bucket on a noncombustible, insulating platform, like an oven pan or oven rack supported by bricks. He says a 2-gallon bucket of hot rocks will heat an average sized room for hours.

Sue

Interesting. I wouldn;t discount it but, speaking only about heating an avg size room for hours, I'd either have to try it or see if you or someone else does and reports back. My suspicion is it might take the chill out of the room if the outside temperature were just a little chilly, but on a cold, cold night? hmmmmm better than nothing at all.

We heat our home with nothing but a woodburning stove....a nice one, I'll grant. but still just a fanless woodburner. So, without a lot of detail, I'd be highly suspect of the claim that a 2 gal bucket of rocks would do more than take the chill off, and then only as long as you were sitting right by it. This is not to undermine the general idea of bringing the heat in though.

I think that this goes under the "I have to see it to believe it" heading. Having said that this could be very useful if you are in a small camper or some other confined space. I would caution about "cracking and exploding rocks" in an open fire.

Are you in a position to try this?

I live in a high-density housing area, and roaring fires - even in emergencies - would be a problem. Getting combustibles would be a problem. And while I trust myself, I see no reason for strangers to trust my ability to keep from burning down the neighborhood; and I'm scared at the thought of a neighbor building a roaring fire.

Too many rocks explode when heated. I doubt that concrete or bricks would, but I'm stuck on where I'd come up with them. (Frankly, rocks would be a problem, too.) And I'd still be concerned about concrete and bricks popping out of my pan.

And like another poster, I have no hope that hot rocks would heat a room. I've lived in houses where the only heat was from a wood burning stove (with a connection to a flue), and it takes a lot of wood and a lot of work to heat the room the stove is in. (This is in Texas, where overnight lows are the low to mid 20s - not especially cold.)

I'd want to try that before I had to depend on it - and I'm not in a position where it's possible to try it.

I agree about the rocks. However the general principle is sound. A few thoughts I've had on this are:

A) heat ceramic bricks (maybe purpose built) and transport THEM indoors.

B) heat cast iron and bring it indoors.

C) Heat hot water and use the power of convection to circulate it with impromptu piping throughout your house (possibly a more long term solution)

D) Heat water in a big cast iron dutch oven and bring it inside.

There's also the good old 'mr buddy' heater which has an automatic low oxygen shutoff switch. I plan on purchasing one as soon as I have a free 85 dollars.

I have a carbon monoxide detector in my townhouse and recommend everyone get one if possible.

In that respect my plan in an emergency is I have about 3 days worth of spare propane. I will bring the propane stove indoors and run it in spurts while having a window(s?) cracked. At least until I can get a mr. buddy.

If that fails, I'll build a mini wood stove out of some old steel cans, a barrier material to avoid fires (such as brick) and some steel ducting from the home supply store to ferry out the fumes.

More than likely though I'll drive the 30 miles to my sister's house and bum in with her since she has a real wood stove <img src="/images/graemlins/smile.gif" alt="" />

I'd guess the other way. Bricks and concrete are more porous than most stone, so they would be more likely to absorb water and thus crack or explode. Just a guess.

Probably a much safer (and more effective) route is the old heated water bottle in your sleeping bag trick.

-john

I'll have to try it and report. I'll also heat up some smaller rocks and see if it really boils water like I've read.

Also, rereading that section of the book, he says they should be "red hot". I don't think I've ever seen a red-hot rock.

Half the people around here say all the rocks here are glacial. The other half say it's old river rock. I guess I'd better find some dry bricks...

Sue

"...I guess I'd better find some dry bricks..."

I'd suggest that you find some dry FIRE BRICKS, not your old everyday bricks...

Sorry, I did mean fire bricks. Slip of the fingers. I have to buy some new fire brick liners for the wood stove, so I'll just collect the broken ones and heat 'em up.

But thanks for the warning. <img src="/images/graemlins/smile.gif" alt="" />

Sue

Ya gotta watch those finger slips, no telling what might happen. Let us know how this little project works (altho I fear that it will take waaaayyyy too much wood to really be effective)...

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?

In my home we use propane for our furnace. Eventually our plan is to buy/install a propane-run generator. Then we'll be self-sufficient heat-wise. The propane will provide the electricity to run the propane-burning furnace.

Of course that will only last as long as the tank (pretty big) or as long as we can get deliveries. Where I live the propane will probably last longer than burning wood would. (no wood to speak of on my small acrage "gentleman's" horse property.

Maybe you could get install a small propane furnace in-line with your current furnace - whatever it is (electric or natural gas), though I'm not sure how cost effective that would be.

Ken K.

I'm wondering if water might be a better medium in some cases than rocks or bricks. By weight, water has five times the heat capacity of granite, for instance. However, you are limited to boiling as an upper limit. If you used 70F as your lower limit at which the heat was no longer useful, you'd have to heat a pound of rock to almost 800 F to store the same energy as a pound of boiling water.

It does seem clear that a nalgene bottle filled with boiled water would make a better foot warmer for your sleeping bag than an 800 degree rock.

Actually, I do have a small wood stove, but I was wondering if I could make it do double-duty by having the normal fire going with rocks or bricks in it, then remove the bricks with fire tongs to a large SS pot (2 or 3 gallons), and moving the bucket to the other end of the house for warmth there.

But mainly it seemed like a good way for people who have the means to build a fire outdoors but not indoors to have some heat when the power goes off. My neighbors have a small baby and a pellet stove. Had our power gone off (we were lucky in the last WA outages), they could have used this method.

But a related question on safety: So I've got my pot of hot rocks or bricks... if I set three 2-hole concrete bricks in a triangle, with a regular oven rack setting on them on a vinyl floor, would that be safe enough, or would there still be a combustion issue below? (I know not to leave anything nearby.) How about carpeting below?

Sue

Hi
I read the same thing about 12 years ago and immediately had to try it out. It's amazing how well this works !
For people weary of exploding rocks, rest assured that ordinary red brick is safe to use. Because it is so porous any water present in the brick is free to check out any time it wants without building up any pressure during the heating process. Though it is not impossible a brick may crack after repeated use, it will not explode !
Ever heard of brick walls detonating in a housefire ? <img src="/images/graemlins/crazy.gif" alt="" />
I once used this trick in an emergency when there was a blackout at around 10.15 PM and it was freezing outside. As the temp inside started to drop I remembered this and fired up the bbq and grilled 8 red bricks, 4 at a time for a little over an hour (75 min. I think it was).
Hauled them inside in wire baskets and although it didn't heat up like a sauna and despite the fact that my home is not that well insulated it did keep the inside temp at a comfortable 18 degrees Celcius (64.4F) during the night till power was restored at around 05:30 AM.
Since I used a charcoal fire for this it may have been hotter than your regular wood fire but I'm not sure.... However I think I got excellent milage from the hotbrick-trick
Regards,
Pharaoh.

> fired up the bbq
Now that solves my fire in the neighborhood problem. Of course, my BBQ is propane-powered, but that just means I have to have a few hours' worth of fuel and some bricks! No bricks in my neighborhood.

Susan,
If you're speaking of large "cinder-blocks" (8"x8"x16" nominal), which will give you 8" of clearance, I would think that would be plenty of room to protect whatever flooring was beneath it, even carpeting. Espcially if you left a little space between the corners of the blocks where they met in your triangle formation. Vinyl flooring is pretty tuff and usually won;t mar even if you set a scorching-hot pan directly on it for a few seconds, so I would think it could handle quite a bit of radiant heat.

I'm thinking the biggest problem would be having one of the hot rocks roll off the rack and onto the flooring and, before you could pick it up, it might scorch something. Of course, you were probably planning to use a bucket of rocks on top of the grill, so that would solve that. Ok, I scrolled up and re-read.... you have a bucket of rocks.