I'm thinking of converting our loft from forced air to cast iron radiators. I'm doing it for the comfort, but is it more efficient?
2nd story, 1930's brick building located in the Midwest.
Aaron: I assume that you're doing this as part of a major remodel, since you'll need to buy a new boiler to replace your forced air furnace, and installing the pipes for the new heating system will entail ripping open walls and floors. Assuming I'm correct, then -- all other things being equal -- the answer to the question of whether a boiler is more efficient than a forced-air furnace is basically "no." It might be more comfortable and quieter, both of which might be worthwhile, but a boiler system will not be more energy efficient than an equally-efficient furnace (i.e., an 80% efficient boiler vs. an 80% efficient furnace). The reason it's not more efficient has to do with how heat flows through the shell of the home -- the walls, ceiling, windows, etc. Heat inside the home will escape to the outside at the same rate, regardless of how that heat is created. Now, if your current furnace is 80% efficient (if it has a metal flue, then it is 80% or lower) and you replace it with a 90% or higher "condensing" boiler, then YES, it will be more efficient. So if you're remodeling and want to install a boiler and radiators for comfort or other reasons, be sure you install a high-efficiency boiler to make sure you wring as much heat out of it as you can. Andy Mazal BPI Building Analyst www.efficiencycafe.com