IM 907 / Page 9 of 4
Prior to Operation
1. Make sure fuses are installed in fused disconnect
switches.
2. Check all electrical connections to assure they are
secure.
3. Check rigidity of unit mounting. Tighten all
fasteners, if necessary.
4. Inspect piping, strainers, traps, fittings, etc.
Initial Start-Up
1. Set thermostat to lowest position.
2. Turn on power supply to unit.
3. Open return gate valve, and then open supply gate
valve to unit.
4. Raise thermostat setting to desired position.
5. Adjust louvers (if provided) for desired heat distribution.
6. To insure proper sequence of operation, cycle unit on
and off a few times by raising and lowering thermo-
stat setting.
7. Check for proper rotation of fan. All fans must rotate
in a clockwise direction when viewed from the front
(UHH) or bottom (UDH) of the unit heater.
Automatic Control
Control Sequences
The following control sequence descriptions are com-
monplace for steam/hot water horizontal and vertical air
delivery unit heaters.
Continuous Fan Operation - Intermittent Hot/Cold
Coil -
A room thermostat controls a valve which opens to
allow steam or hot water to supply the unit and closes to
shut off the supply when the thermostat is satisfied. The
fan runs continuously.
Intermittent Fan Operation - Hot Coil
-
A room ther-
mostat starts and stops the motor when a thermostat calls
for heat, the motor is energized. An aquastat is some-
times strapped to the supply or return piping to prevent
fan operation when heat is not being supplied to the unit
heater. The heating fluid is continuously supplied to the
unit heater, even with the motor off. After thermostat is
satisfied, motor is de-engergized.
Intermittent Fan Operation - Intermittent
Hot/Cold Coil -
To prevent a unit heater from deliver-
ing cold air when the thermostat is “calling for” heat, an
aquastat prevents fan operation when the heat supply to
the coil is interrupted. Conversely, the aquastat energizes
the fan when the automatic supply valve opens to allow
the heating medium to enter the unit heater coil.
Energy Saver – Optional Control
An “Energy Star” control used with vertical air delivery
unit heaters can automatically deliver warm stratified
air to the zone of occupancy, minimize ceiling heat loss
and overall energy consumption. Two thermostats and an
auxiliary switch are required for one or more unit heat-
ers, plus a two-position supply valve for each unit heater.
The room thermostat controls the two-position supply
valve to each unit heater. An auxiliary fan switch stops
the unit heater fan when the supply valve is closed. The
other thermostat (“Energy Saver” Control) is located near
the vertical unit heater at the ceiling or roof where warm
air tends to stratify.
The room thermostat will automatically signal the supply
valve to close when its setting has been “satisfied”. How
-
ever, the thermostat mounted near the unit heater can
override the auxiliary switch to allow the unit heater fan
to run with the supply valve closed, until the temperature
at the higher level falls below the set-point of the higher
mounted thermostat.
Additionally, air delivered by a vertical unit heater
located in high ambient temperatures prevalent at the
upper levels within a building is excessively buoyant and
frequently prevents the unit heater fan from delivering
the heated air to the occupancy level of the building. By
recycling the heat which builds up at these higher levels,
the two-thermostat control arrangement contributes to
increased comfort and lower heating costs.
Operation
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