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.
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