Low-voltage Controls
Requirements
• 18 AWG solid wire or greater.
• Low voltage wiring must be routed through the hole
that is to the left of the high voltage strain relief.
• Keep control wires as short as possible.
Wiring Procedure
The humidifier can be connected to the following three
devices (Fig. 23):
1. Humidistat or thermostat
2. Air Proving device (recommended)
3. External fan (required when used with a humidistat).
Main Supply
L1 L2/N GND
Air Proving
Humidistat
External
Fan Interlock Wiring with HumidiPRO
When distributing steam into a duct, there could be a call
for humidity when there is no air flow. The HM750 with
HumidiPRO control or some other thermostat can be
used to enable a fan on a call for humidity. If using another
thermostat, consult that control's manual for wiring
instructions to enable the fan with a powered
humidification device.
NOTE: Humidifier will stop producing steam if the air
proving switch is open or the air proving terminals
AP are not jumped.
AIR PROVING
(OR JUMPER)
1
AP
AP
24VAC
COM
HUM
HUM
THERMOSTAT, HUMIDISTAT, OR EQUIPMENT INTERFACE MODULE (EIM)
1
AIR PROVING JUMPER COMES PRE-INSTALLED.
REMOVE JUMPER IF AIR PROVING IS UTILIZED.
2
WIRING FOR FAN INTERLOCK EQUIPMENT (REQUIRED WHEN USED WITH
A HUMIDISTAT)
2
GT
RF
GF
Fig. 23. Wiring the steam humidifier with a digital thermostat.
Humidistat or Thermostat Connection
Connect a humidistat or thermostat to the HUM terminals
of the humidifier. The humidifier provides a 24-VAC source
to power the humidistat or thermostat if needed (5 VA max.).
NOTE: It is acceptable, but not recommended to install
the HumidiPRO in the furnace area (on duct). If
possible, locate the HumidiPRO in a high traffic
area inside the home.
Air Proving Device
Resideo recommends the use of an Air Proving device
such as Resideo Differential Pressure Switch (50027910-
001) to ensure steam is distributed only when there is air
circulation. Connect the air proving device to the AP
terminals. If you do not install an air proving device, place
a jumper between the AP terminals.
Fan Interlock
Connect an external fan (optional) to the EXTERNAL
terminals. The fan will turn on whenever there is a call for
humidity.
This information is relevant to all controls, factory
supplied or otherwise. For wiring use minimum 18 AWG
solid wire and keep as short as possible.
Humidity Control
• Can be located either in return air duct (preferred) or in
room being humidified.
• Avoid placing near discharge diffuser of humidified air.
• Mount in area representative of room humidity (drafts,
doorways, sunlight, or an overhang such as a shelf can
affect reading).
Optional Outdoor Temperature Sensor (included with
HumidiPRO)
• Mount outside in area representing air temperature.
13
HM750A1000
Equipment Interface Module (EIM)
M36863C
33-00289EF—05