RH-D AND RH-W ELECTRIC DUCT HEATERS
5
1.800.627.4499
INSTALLATION, OPERATION AND MAINTENANCE MANUAL
RENEWAIRE.COM
OVERVIEW
NOTE: This unit is a
high-voltage open coil
electric heater, used for
both commercial and res-
idential applications. It is com-
monly referred to in this manual
as an “electric heater”.
1.0 OVERVIEW
1.1 DESCRIPTION
1.2 APPLICATIONS
1.4 AIRFLOW DIRECTION
The RH-D and RH-W heaters are open-coil, electric resistance duct heaters that come in several
different models with different wattages and duct sizes. The RH-D heater has an internal temperature
sensor mounted in the outlet side of the unit and has an adjustable thermostat that determines what
the outlet air temperature is to be. The controller then modulates current to the heating coil to maintain
that temperature setting. The RH-W heater requires an external analog 0 - 10 VDC control signal,
supplied by wall-mount thermostat, a RenewAire Premium Commercial Controller or a BMS. A wall-
mount thermostat is provided with each RH-W unit. Every heater is equipped with an airflow sensor to
detect minimum allowable airflow. If there is inadequate airflow, current to the heating coils is reduced
to a level that corresponds to the detected airflow volume. All heaters use a Solid State Relay (SSR) to
modulate the heat output.
1.4.1 RH-D
1.4.2 RH-W
Airflow direction in the RH-D must be coordinated with the Output Air Temperature Sensor.
The sensor
must be located on the outlet side of the unit in order to properly monitor the output temperature.
See the illustrations on page 7. If airflow direction other than as shown is desired, the sensor must be
relocated to the alternate location, as shown.
Airflow direction in the RH-W can be in either direction, with no changes to the unit hardware.
1.3 SAFETY FEATURES
1.3.1 Low Air Flow Modulation / Shut Off
The heater has a thermistor air flow sensor that will detect any overheating condition caused by low
air flow. The sensor has a threshold of 111º F [44º C]. If a temperature higher than 111º F is detected,
it will cause the controller to begin reducing the pulse width of the control signal being sent to the SSR.
The reduction in pulse width begins at a detected temperature of 111º F and the reduction will increase
proportionally up to a detected temperature of 124º F [51º C], at which point the sensor will shut off the
control signal to the SSR. In this mode, the unit’s Red (or Yellow) warning light is ON steady.
1.3.2 Auto-Reset Thermal Cutout
The heater has an auto-reset thermal cutout having a threshold of 125º F. If a temperature higher than
125º F is detected, the auto-reset cutout will shut off power to the heater element. Once the detected
temperature drops below 125º F, the cutout will reset itself and restore power to the heater element.
1.3.3 Manual Reset Thermal Cutout
1.3.4 Maintenance
The heater has a manual reset thermal cutout having a threshold of 200º F. If a temperature higher
than 200º F is detected, power to the heater element is shut off until the heater cools and the cutout
is manually reset.
There is no required annual maintenance for these units.
These heaters are ideally suited for use in tempering air that is delivered directly to an Occupied Space
or they can also be used as a primary heat source. They can be used as pre-heat or post-heat devices
in conjunction with an ERV or a DOAS. The RH-D can operate independantly by setting an on-board
potentiometer to maintain a constant output temperature while the RH-W uses an external temperature
control signal (wall thermostat) to modulate the heat output. These heaters are suitable for use in both
residential and commercial applications.
