month I would like to discuss on-demand (also known as instantaneous
or tankless) water heaters.
are basically two types of water heaters, storage type and
tankless. Storage water heaters are still the most popular
in the United States due to the higher initial cost of tankless
and the flow demand limitations of some units.
type heaters keep water at a 120-140 degree constant temperature
ready to use. This is a waste of fuel and can represent 10-20%
of energy costs. In a tankless heater water is only heated
when there is demand (flow). Once activated the unit continues
to heat water as long as there is demand. The elimination
of continuous storage of heated water can substantially reduce
standby heat loss thus saving energy. Since demand water heating
required more BTU's when operating than standby you will notice
units designed to replace a 40-gallon storage type heater
(usually about 40-50K BTU) will be about 125,000 BTU's.
heaters are easily installed and occupy much less space than
a storage type. In high flow conditions (multiple bathrooms)
several units may be necessary strategically placed near bathroom
groups or centrally located and connected in series to provide
high volume heated water.
every one of these units I have seen (whether electric or
fuel gas) is clearly labeled with minimum clearances to combustibles.
Of course the clearances are much less for electric models.
of these units are factory supplied with overheat sensors
to auto shutoff. However, the IRC requires any equipment used
for water heating or hot water storage to be equipped with
pressure and temperature relief. Most units have tappings
specific for this valve. Some units have anti-freeze protection
wherein the unit turns on intermittently if the temperature
drops below freezing.
have included an illustration of a typical fuel gas fired
tankless water heater for further demonstration.
talk next month,
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