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Auxiliary Heater
Most installations in northern climates include an Aux-
iliary Heater (mounted either internally or externally
depending on the model). Auxiliary heaters are used
for two purposes:
• To supply back-up heat during cold outdoor
temperatures
• To provide emergency heat if the unit’s
compressor
fails
Back-up Heat
Your geothermal unit will provide the largest majority
of your heating. The amount of heat provided by the
auxiliary heater will vary from house to house depend-
ing on factors like climate, unit sizing, heating load,
and economics.
Economically, there is a point (outdoor air temperature) where it makes sense for the geothermal unit to work in
conjunction with the auxiliary heat. When considering both the cost of installation and the cost of operation, it often
makes sense to size the geothermal unit to provide something less than 100% of the total heating requirement.
Generally, sizing the unit in a northern climate to provide 100% of the heating does not make sense economically
because the added initial cost of the larger unit and earth loop may not be recovered in energy savings over a rea-
sonable period of time.
For example:
Installation Option A: The geothermal unit is sized to provide 95% of your heating requirement with the other 5%
using the auxiliary electric.
Installation Option B: The geothermal unit is sized to provide 100% of the heating load.
Assume the cost to operate the auxiliary heat (in Option A) is $50 per year. And the additional cost of the larger
system (Option B) is $2,000 more.
So, dividing $50 (savings) into $2,000 (additional investment) yields a 40-year return on investment. You can easily
see why it makes sense to size the system to allow auxiliary electric to provide some of the heating requirement.
Oversizing the unit may not be cost effective, and it can also lead to decreased comfort and additional wear and
tear on your unit. Units that run for very short periods of time actually incur more stress on the compressor than
units that run for longer periods.
WaterFurnace dealers are trained and have the design tools to determine the most effective size system for your
home considering performance, comfort, installation cost and operating cost.
Emergency Heat
The other reason for the Auxiliary Heater is to provide heating in the event of a compressor failure. Switching to
Emergency Heat mode on your thermostat will provide the home with a source of heat until the compressor is re-
placed.
PRODUCT INFORMATION FOR UNITS, OPTIONS & ACCESSORIES
