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COMMISSIONING
Notes on Aux Heat
» The aux heat source must always have a self-protection mechanism
to turn off if overheating is detected since the indoor unit fan may
be turned off unexpectedly for defrost operation or due to a system
error.
» A thermostat aux heat source should not be added to a dual-fuel
system (gas furnace with heat pump) or to an air handler with a
heater strip. If this is done the thermostat will make a best attempt
to control multiple aux heat sources appropriately, but the heat pump
lockout may not work as expected.
» If a thermostat aux heat source is added to a system with a DTA
furnace adaptor, fan control should be disabled. The aux heater
will be shut down when no fan feedback is received from the DTA
adaptor.
» In an EWC zoning system:
– An aux heat source that doesn’t require the system fan can be
configured as either the primary or secondary heat source.
– If the aux heat source requires the system fan, the heat pump
should always be the primary heat source with no heat pump
lockout so that the zone damper will be open and the system fan
running when the aux heat source is active.
– If aux is configured as the primary heat source or if the heat
pump is locked out, the fan will only run and the zone damper
open when no other zone is calling for heating or cooling. This
configuration should be avoided.
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