2
W43A Humidistat Product/Technical Bulletin
I
ntroduction
IMPORTANT: The W43A Humidistat is designed for
use
only
as an operating control.
Where an operating control failure
would result in personal injury and/or
loss of property, it is the responsibility
of the installer to add devices (safety,
limit controls) or systems (alarm,
supervisory systems) that protect
against, or warn of, control failure.
The W43A Humidistat provides SPDT control for use
on low or line voltage applications. It has a
thermoplastic cover with Allen-head locking screw to
discourage unauthorized tampering. The sensing
element consists of carefully selected and processed
human hair.
An adjusting knob and easy-to-read dial allow quick
selection of the desired setpoint. The humidistat is
supplied with the faceplate installed for vertical
mounting and knob adjustment. However, a horizontal
faceplate is enclosed for horizontal mounting and knob
adjustment if desired.
H
umidity Settings
The humidistat has a setpoint range of 0 to 70% RH,
as well as humidification off (HUM OFF) and
dehumidification off (DEH OFF) positions. At the HUM
OFF position, the C to L terminal circuit is open and
the C to H terminal circuit is closed.
At the DEH OFF position, the C to H terminal circuit is
open and the C to L terminal controls the
humidification equipment.
At any given setpoint, the C to L circuit closes on a
decrease in relative humidity, and the C to H circuit
closes on an increase in relative humidity.
The usual setting in winter is 30 to 40% RH. Lower
settings may be necessary in extremely cold weather
to prevent condensation on windows, doors, etc. The
same setting should be used where reduction of
humidity by means of exhaust fans is provided in well-
constructed homes. Summer settings on air
conditioning or dehumidifying equipment will usually be
near 50% RH.
The suggested indoor humidity at 70
°
F (21
°
C) for
residential applications on humidifying or dehumidifying
equipment in winter is shown in Table 1.
Table 1: Humidity Settings
Outside Temperature
Suggested Humidity
Setting
-20
°
F (-29
°
C) and Below
15% RH
-10
°
F (-23
°
C)
20% RH
0
°
F (-18
°
C)
25% RH
10
°
F (-12
°
C)
30% RH
20
°
F (-7
°
C)
35% RH
Above 20
°
F (-7
°
C)
40% RH or Higher as Desired
I
nstallation
Supplies Needed
•
2 x 4 in. (51 x 102 mm) wall box (field supplied)
•
3-wire cable (field supplied)
•
screwdriver (slotted standard)
•
marking pencil
•
wire strippers
Location Considerations
Locate the W43A Humidistat as follows:
•
on an inside wall away from ranges, sinks,
bathrooms, or other areas of extreme moisture
and temperature
•
where natural air circulation is unrestricted
•
where lamps, sunlight, fireplaces, heat registers,
radiators, concealed air ducts or pipes, or room
occupants will not affect its operation
