The first thing to consider are the fuels available, the cost of the fuel, and if you are concerned about the environment. Then, you need to be aware of the effect your choice will have on the environment.
     The leading cause of pollution associated with the home is the inefficiency of the structure itself. The loss of heat through the structure causes thermal pollution directly and causes more fuel to be burned indirectly. The next effect on pollution is the type of fuel, how efficient the appliance, and how clean are its emissions.

    1.  WOOD:  Although most wood burning boilers can be made to burn somewhat clean during testing, in actual use they perform poorly both in efficiency and emissions, and should be considered only if wood is readily available. We do offer the one exception, the Seton Wood Boiler is the cleanest burning wood boiler in the world. See www.rohor.com
    2. OIL: Fuel oil is the same as the diesel used by trucks and some auto's. It comes in two grades, number 1 and number 2. No.1 burns slightly cleaner than No 2 but uses more fuel and costs more. The best oil burning appliance is only 86% efficient. Some manufactures claim 98 % or better, but their claim is based on being  98% of 86%. Oil boilers require regular maintenance. After cleaning and servicing, an oil boiler will lose 12% efficiency in 12 months. If not maintained properly oil boilers cause a lot of pollution. An oil water heater  have the same efficiency as all oil boilers and  require minimum maintenance   
    3.  ELECTRIC:  Although electric boilers are 100% efficient and clean in your home, the power generating plants fuel and efficiency must be considered, also  electric resistance heating is very expensive. We have designed some off-peak power radiant systems, but there is no guarantee that these programs will continue. I do recommend electric mats such as www.warmlyyours.com for small areas that are hard to heat another way.
    4.  GAS:  Natural gas, if available is inexpensive and relatively clean burning. The boiler you choose will effect the efficiency and amount of pollution created. The standard gas boiler is between 80% and 86% efficient. A boiler that is 96% efficient will burn at least 20% less fuel than an 86% boiler and reduces pollutants dramatically, but they are more expensive.
    5.  PROPANE:  Propane has all the advantages of natural gas but is  more expensive. It should only be considered in small, very well insulated homes and only with a high efficiency boiler (96%+).
    6.  GEOTHERMAL:  Before considering geothermal, consider putting the additional money that geothermal would cost into a more efficient design, more insulation or a more advanced construction method such as Sip's, styrofoam block or one of the many new products available. This will give you an extremely low yearly cost for heating and will never need replacing or maintenance and will not be subject to the eventual cost raises of electricity.