My mother lives in a farm down in Somerset, they have an old industrial furnace which heats the water and provides central heating to the house - every few years they buy a couple of hundred bales of elephant grass or similar bio mass and it works a treat, a single bale can provide heating and hot water for an evening, its cheap and it has a zero carbon footprint.

If you have space in an outbuilding close to the house (and if you have the spare land to grow the biomass yourself) then its an incredibly effective and cheap way of getting heating and hot water.

James