> I wonder why furnaces have these fancy high-efficiency heat exchangers and stoves don't? Cost? I don't see how a design like that would work for a range. The

> I wonder why furnaces have these fancy high-efficiency heat exchangers and stoves don't? Cost? I don't see how a design like that would work for a range. The purpose of a range is to heat small, movable objects (pots) to high temperatures (~500°F) with good responsiveness (= short time constants). The purpose of a furnace or water heater is to heat fluids contained in large spaces or tanks to modest temperatures (~100°F) with very limited responsiveness (= long time constants). The heat exchanger really helps the case of heating a stream of fluid, as that's where the exchange is most useful. The physical and thermal mass of the heat exchanger and flue condenser are both considerable. I'm not seeing how to make a gas rangetop significantly more thermally responsive without making it no longer practical. For people who can't abide gas for whatever reason, induction units are supposedly excellent these days. (I've never tried one. They can't possibly be worse than an electric smoothtop range, though!)