20 Combination Water and Space Heating Applications – Commercial Use Water Heaters Only
Commercial use water heaters may be used for space heating or combination space heating/potable water
heating applications, provided the following requirements and recommended piping diagrams are carefully
followed.
WARNING
The following instructions must be carefully followed to assure safe and reliable operation of the
water heater. All piping components connected to this water heater must be suitable for use with
potable water. In Massachusetts, space heating piping length must not exceed 50 feet. Toxic
chemicals, such as those used for boiler treatment, must not be introduced into potable water used
for space heating. This water heater must not be connected to an existing heating system or
component(s) previously used with a non-potable water heating appliance. When the system
requires water for space heating at temperatures higher than required for other means, an ASSE
approved mixing valve must be installed to temper the water for those uses in order to reduce the
scald hazard potential.
1. Only commercial use water heaters may be used for combination water heating/space heating
applications. Residential use water heaters will not be covered under warranty for water heating/space
heating applications.
2. The temperature setting of the water heater thermostat must not exceed 160F.
3. In combination space heating/potable water heating applications that require higher water temperatures
than normally used for potable water uses, an ASSE approved thermostatic mixing valve must be
installed to temper the water for those uses in order to reduce the scald hazard potential.
4. In order to assure adequate flow through the water heater, follow the recommended piping diagram and
circulator specifications (see
5.
6. Note: in Massachusetts, the following must be done:
Tempered potable water must meet temperatures in 248 CMR.
All water piping must be insulated in accordance with 780 CMR (Massachusetts energy code).
50 feet maximum distance from water heater to space heating load (developed length).
Piping loop between water heater and heating load must be in compliance with 248 CMR.
All circulators must use an electronically controlled timer that activates every 6 hours for 60 seconds.
7. Figure 7).
8. An expansion tank will be required in all space heating applications.
9. A Y-type mesh strainer (#20 mesh screen) should be installed on the cold water inlet of the water heater
to prevent clogging of the fine mesh screen on the water heater cold water inlet connection.
10. A water softener must be used if the water supply has a tested hardness level above 10 grains of
hardness.
11. All piping must be ¾” copper or larger.
12. All components must be suitable for use with potable water.
13. The water heater should be located as close as practical to the space heating heat exchanger.
14. A check valve should be located after the circulator(s) to prevent backflow during potable water demands.
15. A heat exchanger may be required to separate the potable water from the space heating circuit in certain
applications.