Propane tankless water heater. Want hot water on demand without ever having to store the excess in a tank? That's the promise filled by a propane tankless water heater. The devices circulate water through a series of burners activated by the flow. The output is a constant stream of hot water for a shower, laundry, the dishes and other tasks that are commonly supplied by a space-hogging, energy-wasting hot water tank.

The heaters, which can also operate with electricity or natural gas, range from about $500 to $1,500. The additional cost over a conventional water tank is recouped over time as they shave 10 to 20 percent off costs to keep tank water hot. But if hot water demand exceeds the system's capacity, some users may be left in the cold. Propane is also portable, which makes it a good option for off-grid living.

Photo: Bosch