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When a hot water faucet is turned on, water is heated as it flows through a heating coil or heat exchanger installed in a main furnace or boiler.
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Indirect systems can be fired by gas, oil, propane, electric, solar energy, or a combination of any of these.Ī tankless coil water heater provides hot water on demand without a tank. An indirect water heater, if used with a high-efficiency boiler and well-insulated tank, can be the least expensive means of providing hot water, particularly if the heat source boiler is set to "cold start." The energy stored by the water tank allows the furnace to turn off and on less often, which saves energy. An indirect water heater uses the main furnace or boiler to heat a fluid that's circulated through a heat exchanger in the storage tank. Indirect water heaters are a more efficient choice for most homes, even though they require a storage tank.