Tankless Water Heaters

Coil Systems

Homes with a hydronic (hot water or steam) home heating system can use the tankless or coil system. A pipe coil built into the boiler and the water from the the cold water supply is heated as it passes through the coil. To accommodate periods of high demand, small storage tanks are sometimes connected to increase hot water availability. A cold water mixing valve is usually installed as a safety device to prevent scalding. Due to the extremely high temperature of a boiler, the hot water leaving the coil is beyond the safe limit of 120° F to 140° F. The mixing valve tempers the hot water by adding cold water to the hot water leaving the coil.

Generally, these systems are advantageous in regions where the furnace is on most of the year. There is no cost for maintaining and heating a large volume of stored hot water, and by sharing the boiler, no separate heat source and fuel is needed. However, during warm seasons, the boiler will have to generate the same amount of heat used to heat the house but only to heat the water. As a result, the the fuel saving is lost.

Instantaneous Hot Water Heaters

In addition to boiler-mounted tankless heaters, stand-alone units are available. Gas-fired instantaneous water heaters have a heat exchanger with a built-in coil. Like boiler-mounted systems, water from the the cold water supply is heated as it passes through the coil. Likewise, there is no cost for maintaining and heating a large, stored volume of hot water. However, stand-alone units typically have a lower flow rate than boiler-mounted systems and may fall short during periods of high demand.