I have an oil
fired boiler that gave 250° F water
at 15psi. It ran thru uninsulated copper pipe to baseboard type radiators. In cold weather
it burned 5+ gallons a day.
I changed the baseboards to marine
forced air heaters, insulated the pipe and turned the water temp to 180° and cut the oil
bill in half. Later I completely replumbed with insulated CVPC and also added plumbing
so I can use engine water to heat when cruising. I also have a pellet stove with a coil that heats the boiler when running and eliminates the need for oil. Since I maintain below 180° the CVPC pipe works fine. I have pressure relief valved at the boiler and pellet stove.
The forced air heaters heat 4x as fast as the radiators. I can go from a cold boat, cold boiler to comfort in about 30 minutes. Also I can circulate the boiler water thru cold engines prior to starting. Usual water additives. Be careful of anything that could make steam. Water expands 16x going to steam and makes pressure fast.