We have a coal furnace and this past winter we were financially very tight and couldn't afford enough coal to keep the house warm. Dad and the boys came up with a way to rig the coal furnace to burn used motor oil. They drilled a small hole in a plate on the back of the furnace and put in a little copper tube. The oil was siphened and dripped at a slow rate from the bucket. It worked really well and we stayed warm. It was very inexpensive in comparison and was a way to use up the old motor oil.

I forgot to mention, we are thinking about using used veggetable oil this year. The motor oil worked well, but it was a mess when it got on stuff. The veggetable oil would smell good I think.

Any comments or suggestions? The furnace is in the basement and heats water radiators throughout the house.

Read through the verious posts in the "biodiesel for heating" section of this forum here. The link there to the "altfuelfurnace" forum will keep you reading for weeks, many folks are burning both UEO or veg. Any of the heavier oil needs to have heat added to it to burn reliably and cleanly. There are a couple of basic burner desighns that add adiquate air to burn the fuel cleanly, a normal home fueloil burner can be modified to burn it well.

What type of coal furnace do you have? if it has the huge outside shell you likely could add a fueloil burner (burning whatever) through the shell and be able to use either the oil burner or the original coal/corn burner.
What does coal cost/ton in Idaho? Illinois supplied scads of coal for big electrical generators but I have not been able to find an outlet that actually sells the coal to the public, I am told that the local Amish community has to have it trucked in by semi truck from Pensylvania. I got about 1/2 ton a few years ago out of a basement and found it to be a very nice geat source, a lot less work than wood, I just can't buy it locally.

You might also consider shelled corn as fuel, it should work directly in a stoker coal burner and feed-auger system (may have to reduce the amount of air to the burner, would have to test this) and it is clean, if you spill it on the floor you just sweep it up, no mess. Corn is a LOT cheaper than either propane of fuel oil if you have to buy it, don't know how it compares to the cost of corn. one bushel of corn containes the same energy as about 3 gallons of UEO or diesel/fueloil. Corn runs about $2.75/bushel so it's heat costs about 1/3 the cost of oil, well - not as cheap as FREE oil though. Used engine oil is scarce in my small town as both of the local auto repair shops burn it in there furnaces.