I wish to retrofit my home for heat. Currently it only has cadet electric heaters. It is in a remote are of NW Montana. My research has led me to believe a a hot water hydronic system with piping installed in the joist spaces under the sub floor at the crawl space. Do you have any recommendations on the type of energy source to use for the boiler/heater?

One story house?

While electric is more efficient, it is more costly. It also heats water up slower than gas due to BTU output. Do you have reasonable access to propane? Since you have a long heating period, get at least a 500 gallon tank and if possible buy it instead of leasing, you get better pricing, at least in GA, I do. How cold does it get there. Personally, I would go with propane.