What can't you burn in the Rocket Mass Heater

I was thinking about Paul's discussion on what to do with a pizza box this weekend. I unfortunately have a lot of unusable cardboard left over from where I work and I hate filling up the trash bins with it so into the stove for starting a fire it goes. I also have been experimenting with using the North Idaho Energy logs which are pretty cool and burn quite well in my 8" batch--they are held together from pressure and not with glues like other energy logs. But what else can we safely toss into the rocket mass heater to burn instead of putting into the landfill. I know countries like Sweden are burning their trash to create energy for the country, but those must be extreme temperatures to reduce emissions. Any thoughts?

I suppose if it was once a tree or grass product, it is ok to use cardboard.

Coal doesn't work very well.

One of the tough parts to that is knowing for sure what is actually in the fuel. For example, any heavy metals or carcinogens in the inks or binders for cardboard or paper? Do we really know for sure? While a good draft and well sealed RMH protects those inside for anything that comes out the other end, someone in your yard or a neighbor downwind could still suffer the results.

If you live in a rural area and are using a trash barrel regardless, I would still be careful of burning nasty stuff indoors, just in case there's not a strong draft to keep the gick out of your breathable air.

Mark Tudor wrote: For example, any heavy metals or carcinogens in the inks or binders for cardboard or paper? Do we really know for sure? .

I looked into cardboard for sheetmulching I found that all the cardboard from North America and Europe used only vegetable inks.  I wasn't sure about Asian sourced cardboard, but I think that they have to use veg ink for our markets, but it's smart to double check for your own piece of mind.

I suspect the safest thing to do if it isn't virgin wood is to compost it, grow trees from the compost, and then burn the dried logs of those trees.