This type of heater is very common in colder countries because of its fuel efficiency. Most households have a piped-in gas line making it convenient to install. This type of heater uses gas to start a flame, which heats the water that passes thru a heat exchanger (similar to a car radiator) built in the unit. A.O. Smith Water Products
Oil
This type of heater is typically found in older homes that already use oil as their heating fuel as well. The hot water output is usually very high. Bradford White - oil water heater
Combination water heating/space heating
This type of heating vessel has the ability to heat both your domestic hot water, in addition to heat water for space heating. One advantage of this type of heater is it can take the place of both a small separate boiler and water heater. Bradford White - Combicore water heaters
Electric
This is the most common of all water heaters. It converts electricity into heat, thus heating water that passes thru the heater. A.O. Smith Water Products
Point of use
A point of use water heater is a very small water heater, tank or tankless, that is designed to be installed at the point of use, thereby eliminating a long pipe run. They are mostly sized to supply hot water to one specific application, usually a sink. They can be either a mini storage tank or tankless water heater. A.O. Smith Water Products
Instantaneous
This whole house unit heats water the instant there is a demand and increases its output as flow increases. It's economical because it only consumes gas when there is actual demand for hot water; there is no standby heat loss. Rinnai - water heaters
