Indirect Water Heaters
water heaters are another form of combination heating/water
heating system. In contrast to tankless coil models, indirect
water heaters utilize a storage tank.
An indirect water heater uses the main furnace or
boiler to heat a fluid that is circulated through a heat exchanger.
Unlike tankless coil units, the heat exchanger in the indirect
water heater is located in the storage tank, not the furnace
or boiler. An alternate configuration runs the boiler water
through a jacket which surrounds the domestic hot water tank.
The energy stored by the water heater tank allows the furnace
to turn off and on less often, saving energy.
systems without a storage tank run a coil of the plumbing
for the domestic hot water through the boiler or through a
tank next to the boiler (the tank is filled with boiler water
indirect systems have a very small tank of domestic water
which is not heated until hot water is called for.
Water Heater with Tank
Since boiler water is often treated with chemicals to prevent
corrosion, scaling and bacterial growth, some local regulations
require that indirect water heaters use double-wall, vented
heat exchangers to prevent contamination of the potable water
with the boiler water in the event of a leak inside the heat
Indirect Water Heater
An indirect water heater used with a high-efficiency
boiler and well-insulated tank can be the least expensive
means of providing hot water. Combination systems are measured
by their CAE, combined appliance efficiency rating. Combination
appliance efficiency ratings range from 0.59 to 0.90.
Indirect systems can be fueled by natural gas, oil,
propane, electricity, solar energy or any combination.
Like tankless coil water heaters, indirect water
heaters have few moving parts so maintenance and service is
less than other types of water heating systems.