Rocket Mass Heater for a camping tent

I'd like to run an idea by everyone and see what you think.  I'd like to build a rocket mass heater underneath a family size 10'x10' camping tent and use the soil as the insulation.

Before setting up the tent, I'd dig a trench 8" deep by about 5" wide and make it run about 12' long.  I'd then lay 4" stovepipe down in the trench and cover it over with 4" of dirt. 

Once the trench is filled in, the ground will be back to being level and I can set up my tent over this area.

On one end of the stovepipe that is under the trench, I would need a firebox and on the other end, I'd need to create a chimney that I'm thinking would be about 5' high, with a spark arrestor on top so I don't burn the tent down.

My main questions are:  Will 4" stovepipe be big enough to move the required air?  Will stovepipe melt if I don't have a combustion chamber?  Can I get away with not having a barrel combustion chamber, or if I have one, how would I do it.  Could I get away with something as small as a 5 gallon metal can?  Would one run of 4" stovepipe, 10' long be enough to heat the tent or would I need to have it double back like I've seen in many of the greenhouse rocket mass heater videos?

I'd need for all this to break down into a fairly small package that I can carry in the car.  Most likely on the roof rack due to the soot.  I'm envisioning 2 elbows and about 17' of stovepipe.

Here's a picture of a rocket stove that uses the dirt in the ground as the cooktop.  Basically I want to do this to heat a tent. 

fooboo wrote:
I'd like to run an idea by everyone and see what you think.  I'd like to build a rocket mass heater underneath a family size 10'x10' camping tent and use the soil as the insulation.

Before setting up the tent, I'd dig a trench 8" deep by about 5" wide and make it run about 12' long.  I'd then lay 4" stovepipe down in the trench and cover it over with 4" of dirt. 

You would be using the soil as mass as well. If it was a one night deal... a fire in a pit for a while then filled in over the coals would probably be good enough. So think two plus nights, but not long enough to think perm.

Once the trench is filled in, the ground will be back to being level and I can set up my tent over this area.

On one end of the stovepipe that is under the trench, I would need a firebox and on the other end, I'd need to create a chimney that I'm thinking would be about 5' high, with a spark arrestor on top so I don't burn the tent down.

My main questions are:  Will 4" stovepipe be big enough to move the required air?  Will stovepipe melt if I don't have a combustion chamber?  Can I get away with not having a barrel combustion chamber, or if I have one, how would I do it.  Could I get away with something as small as a 5 gallon metal can?  Would one run of 4" stovepipe, 10' long be enough to heat the tent or would I need to have it double back like I've seen in many of the greenhouse rocket mass heater videos?

The general thought is that 6in is minimum. However, I have seen smaller ones built. You are treading on new territory and so experimenting in the back yard is the way to go. Personally, we have never felt the need for a warmer tent. If we did, then the boat ride to our favourite campsite would be less than enjoyable too. I think what you are describing is not really a rocket heater and if you used your horizontal (under the tent) pipe as your burn hole, it may work just fine... more like a hypocaust. Try it in your backyard... or on the beach, and see how wide the heated zone is.

RMHs are good for some things, but sometimes something else will work better.... Maybe a metal bucket to put heated stones/dirt from around the campfire for example... or the dirt/rocks from the cooker  you showed, put into the frypan and put on top of a piece of wood so it doesn't melt the tent floor.

For that matter sleep closer together.... works for me

This would be for a two week campout and the temps will be down around 30F degrees.

One thing I'm worried about is that soil in the top 4" of so has a lot of organic material.  How hot do you think the stovepipe would get?  I don't want to catch the ground on fire.  The camping will be on private property I own, so I could bring a few bags of sand or even vermiculite with me if needed if it gets too hot.

I agree that I'm exploring new territory here, and a backyard test is definitely in order, but I wanted to get ideas from others who have more experience so I have a better chance of success.

One other thing I thought of...  In the picture I posted, I'm not sure if it is clear, but that person was using the upside down skillet as the combustion chamber.   In other words, the skillet was getting smoke billowing up against it from underneath.  I could do something similar to that by using an old iron dutch oven and have the fire pit and dutch oven about 12" away from the tent, then run the stovepipe under the tent and then up and out through a 5' chimney.

I guess I could go with 6" stovepipe if I have to, but that would be much harder to transport.  Does anyone know of any Youtube videos of RMH's using 4".  I don't want to make the mistake of buying 4" materials and then having to throw it all out and start over if I don't have to.

It is difficult for me to respond, without sounding sarcastic, but i will try.

Since you are the land owner and the experimenter, you will be responsible for anything that goes wrong and injures anyone.

Do you want to add heat to the inside of the tent or impress the campers with a underground rocket stove heating system?

If you want to just get heat in there - then Len's suggestion to heat rocks outside, and then put them in a steel bucket inside, will heat without the added expense and be a lot safer. 

The pic that you have posted and your description of it's use, show a cook stove that has no insulated heat riser. The exhaust of your cook stove will be far more smokey than a RMH that has the insulated heat riser.

The 4" system has been discussed and those with a lot of trial and error experience suggest that 6" is the minimum to work good. I take their suggestion seriously and wouldn't make a 4" system. If someone were to go off and be determined to make a 4" system work,  I wouldn't bet that they can't make it work, I just wouldn't do it without a very good reason and time and money to waste.



If you want to make an in ground system, to heat the ground beneath your tents, there are places in the world that coil hose under their floor and heat water outside and then pour it in the hose where it heats the ground beneath their floor. Once again Len's suggestion wins out as simply practical.

If it were me I'd wait till summer and let the sun heat the ground.

Thanks for your comments.  Hauling rocks into the tent every night is too much trouble.  I could just buy a propane heater and get heat that way.  The goal was to build something that is easy, portable, and efficient, and doesn't require propane or gas.  I'm also looking for something that will put out heat for most of the night.  Hot rocks or a hot water system would leave you waking up in the morning to a cold tent, whereas a RMH would still be putting out some heat most of the night because I could stack up a good amount of wood into the feedbox and let gravity do the rest.

I'm going to try to conduct an experiment using 6" stovepipe and use a 5 gallon metal bucket as the heat riser with an insulated 6" stovepipe riser inside that.   I figure I could put the whole thing together, including digging the ditch, in less than an hour, and takedown would be about the same time. 

I'm hoping that a 5 gallon metal bucket is big enough to fully combust the smoke.  If I have to go much bigger than that, then the whole system will be too big to be portable enough for camping.