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T4398A,B High  
Performance Electric Heat Thermostats  
PRODUCT DATA  
FEATURES  
Controls both fan-forced and baseboard electric  
heaters.  
Temperature-responsive, vapor-filled dual diaphragm  
sensing element provides 2°F (1°C) sensitivity with  
minimum droop.  
UL listed up to 5 kW at 277 Vac.  
Replaces virtually all standard wall-mounted line  
voltage thermostats.  
Includes long-lasting Micro Switch™ mechanism.  
Color-coded leads for easy installation.  
Cover thermometer indicates room temperature.  
Rugged, plastic mounting base.  
Contemporary white finish complements almost any  
decor.  
GENERAL  
The T4398A,B High Performance Electric Heat Thermostats  
provide precise line voltage control of resistance-rated electric  
heating equipment. Snap action switch makes heating circuit  
on temperature fall; T4398B models make double line break  
with setting knob at OFF position.  
Contents  
General ............................................................................. 1  
Features ............................................................................ 1  
Specifications .................................................................... 2  
Ordering Information ......................................................... 2  
Installation ......................................................................... 3  
Settings and Adjustment ................................................... 4  
Checkout ........................................................................... 5  
Operation .......................................................................... 6  
Copyright © 1996 Honeywell Inc.  
All Rights Reserved  
68-0147-2  
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T4398A,B HIGH PERFORMANCE ELECTRIC HEAT THERMOSTATS  
Thermometer Temperature Range:  
0° to 90°F (10° to 30°C).  
SPECIFICATIONS  
5
IMPORTANT  
Differential:  
°F (1°C), nonadjustable.  
The Specifications given in this publication do not  
include normal manufacturing tolerances. Therefore,  
this unit may not exactly match the listed  
2
Setpoint Adjustment:  
specifications. Also, this product is tested and  
calibrated under closely controlled conditions, and  
some minor differences in performance can be  
expected if those conditions are changed. For exact  
engineering specifications, contact your Honeywell  
sales representative.  
Dial on front of thermostat.  
Dimensions:  
See Fig. 1.  
Barometric Sensitivity:  
1°F /500 ft (0.5°C/kPa).  
TRADELINE® MODELS  
TRADELINE models are selected and packaged to provide  
ease of stocking and handling and also maximum  
replacement value. TRADELINE model specifications are  
listed in Table 1.  
Mounting:  
Mount directly on vertical 2 x 4 in. outlet box, or on 4 x 4 in.  
outlet box with ring adapter (ordered separately), using 6-32  
Robertson slotted screws.  
Electrical Ratings (Noninductive Resistive Loads):  
Approvals:  
22A at 120/208/240 Vac; 19A at 277 Vac, 60 Hz.  
Underwriters Laboratories Listed: File no. E47434, guide  
no. XAPX.  
Canadian Standards Association Listed: File no. LR1322.  
Wiring Connections:  
in. (150 mm) copper leadwires, suitable for connecting to  
6
aluminum wiring if approved special service CO/ALR  
connectors are used.  
Accessories:  
272804A Range Stop and Locking Screw Assembly: Includes  
locking cover screws, Tinnerman cilps, wrench and range  
stops—two plastic pins to insert inside cover for field-  
selection of minimum and maximum temperature settings.  
Sensing Element:  
Vapor-filled dual diaphragm.  
Temperature Setting Range:  
50° to 80°F (10° to 25°C).  
Table 1.Thermostat Specifications.  
Model  
Number  
Temperature Rating  
°F (°C)  
Switching  
Finish  
Includes  
T4398A  
T4398B  
Spst; makes single line break on  
temperature fall.  
50 to 80 (10 to 25)  
White  
Cover thermometer, temperature  
range stops and locking cover.  
Dpst; makes double line break  
with setting knob at OFF position.  
50 to 80 (10 to 25)  
White  
Cover thermometer, temperature  
range stops and locking cover.  
ORDERING INFORMATION  
When purchasing replacement and modernization products from your TRADELINE® wholesaler or distributor, refer to the  
TRADELINE® Catalog or price sheets for complete ordering number or specify:  
1
2
. Model Number.  
. Switching.  
If you have additional questions, need further information, or would like to comment on our products or services, please write or  
phone:  
1
2
. Your local Home and Building Control Sales Office (check white pages of your phone directory).  
. Home and Building Control Customer Relations  
Honeywell, 1885 Douglas Drive North  
Minneapolis, Minnesota 55422-4386  
In Canada—Honeywell Limited/Honeywell Limitée, 35 Dynamic Drive, Scarborough, Ontario M1V 4Z9.  
International Sales and Service Offices in all principal cities of the world. Manufacturing in Australia, Canada, Finland, France,  
Germany, Japan, Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A.  
68-0147—2  
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T4398A,B HIGH PERFORMANCE ELECTRIC HEAT THERMOSTATS  
FRONT VIEW  
SIDE VIEW  
CAUTION  
3
/4  
1-3/4  
1/2 (13)  
1. Disconnect power supply to prevent electrical  
shock or equipment damage.  
(
19)  
(
48)  
8
0
2. If connecting with aluminum conductors, use CO/  
ALR solderless wire connectors to avoid fire  
hazard.  
7
6
0
0
50  
˚F  
3. Do not remove thermostat cover until wiring is  
complete to avoid damaging the sensing element.  
2
(54)  
-1/8  
4
-3/8  
(
111)  
3
(
-1/4  
83)  
Location  
Install a vertical outlet box, which is used to mount the  
thermostat on, about 5 ft (1.5 m) above the floor in an area  
with good air circulation at room temperature.  
Do not install the thermostat where it may be affected by:  
2-7/8 (73)  
1-1/2  
1/2 (13)  
drafts or dead spots behind doors, in corners or under  
cabinets.  
M5795A  
(
39)  
hot air from convectors.  
radiant heat from sun or appliances.  
concealed pipes and chimneys.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
Fig. 1.T4398 approximate dimensions in in. (mm).  
RECYCLING NOTICE  
If this control is replacing a control that contains  
mercury in a sealed tube, do not place your old  
control in the trash.  
Wiring and Mounting  
CAUTION  
Contact your local waste management authority for  
instructions regarding recycling and the proper  
disposal of any control containing mercury in a  
sealed tube.  
1.  
Handle the thermostat with care to avoid  
damaging the sensing element or control.  
Use a separate limit control in the heating  
appliance.  
2.  
IMPORTANT  
If locking cover feature is desired, insert the locking  
cover clip in the thermostat base before mounting  
the thermostat on the wall. See Fig. 7.  
INSTALLATION  
Replacement Applications  
 Disconnect power to thermostat to prevent electrical  
shock or equipment damage. All wiring must comply  
with local electrical codes and ordinances.  
 Remove the old thermostat from the wall, taking care  
not to damage the wiring insulation.  
 Check the old wire insulation for cracks, nicks or fraying.  
Apply approved electrical tape to insulate wires or  
replace wires as necessary.  
 Do not remove T4398 Thermostat Cover. Using wire  
connectors approved for No. 12 wires, make line  
voltage connections directly to leadwires on thermostat.  
See Figs. 2 and 3 for typical wiring connections.  
 Prebend and push solid wires into the outlet box.  
 Remove the thermostat cover by grasping the top and  
bottom edges and pulling outward away from the base.  
 Turn the setting dial so the indicator is at the 12 o’clock  
position to prevent damaging the sensing element when  
mounting the thermostat.  
When Installing this Product...  
1
. Read these instructions carefully. Failure to follow these  
instructions could damage the product or cause a  
hazardous condition.  
2
3
4
. Check the ratings on the product to make sure the  
product is suitable for your application.  
. Installer must be a trained, experienced service  
technician.  
. After installation is complete, check out product  
operation as provided in these instructions.  
WARNING  
HIGH VOLTAGE CONTROL.  
ELECTRICAL SHOCK HAZARD.  
Follow local codes and ordinances when installing this  
thermostat. Improper handling can cause serious  
injury or death.  
 Mount the thermostat on the outlet box as shown in  
Fig. 4. Secure the thermostat by tightening the two  
mounting screws.  
3
68-0147—2  
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T4398A,B HIGH PERFORMANCE ELECTRIC HEAT THERMOSTATS  
T4398A  
WALL  
L1  
4
THERMOSTAT  
BASE  
T1  
SOLDERLESS  
CONNECTORS  
ELECTRIC  
6
5
6
0
5
5
0
HEATER  
OUTLET  
BOX  
7
0
2
7
5
SETTING DIAL  
INDICATOR  
0
1
L1  
HOT)  
3
(
L2  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
MOUNTING  
SCREWS (2)  
USE SPECIAL SERVICE CO/ALR SOLDERLESS CONNECTORS  
WHEN CONNECTING ALUMINUM CONDUCTORS OR A FIRE  
HAZARD MAY RESULT.  
M5797  
Fig. 4. Mounting thermostat to outlet box.  
3
4
USE A SEPARATE LIMIT CONTROL IN THE HEATING APPLIANCE.  
New Applications  
 Disconnect power supply to prevent electrical shock or  
equipment damage. All wiring must comply with local  
electrical codes and ordinances.  
BREAKS AND REMAKES BELOW -31°F (-35°C); NORMALLY  
THERMAL ACTIVATED. BREAKS ON TEMPERATURE RISE;  
MAKES ON TEMPERATURE FALL.  
M5791B  
Fig. 2.Typical wiring connections for T4398A.  
 Run line voltage wiring to the thermostat location.  
 Do not remove T4398 Thermostat Cover. Using wire  
connectors approved for No. 12 wires, make line  
voltage connections directly to leadwires on thermostat.  
See Figs. 2 and 3 for typical wiring connections.  
 Prebend and push solid wires into the outlet box.  
 Remove the thermostat cover by grasping the top and  
bottom edges and pulling outward away from the base.  
 Turn the setting dial so indicator is at the 12 o’clock  
position to prevent damaging the sensing element when  
mounting the thermostat.  
T4398B  
RED  
WIRE  
L1  
L2  
6
5
3
 Mount the thermostat on the outlet box as shown in  
Fig. 4. Secure the thermostat by tightening the two  
mounting screws.  
T1  
T2  
ELECTRIC  
HEATER  
SETTINGS AND ADJUSTMENTS  
L2  
L1  
SOLDERLESS  
CONNECTORS  
1
4
Calibration  
2
(HOT)  
The T4398 Thermostats are calibrated at the factory using  
precise instruments under closely controlled conditions.  
Recalibration should not be necessary. Allow the thermostat  
to operate for several hours before checking calibration. The  
T4398 Thermostat vapor-filled dual diaphragm sensing  
element is affected by barometric pressure and altitude.  
Temperature deviations of 1°F (0.5°C) are normal. If the  
thermostat is mounted in a suitable location (as instructed in  
the Location section) and still appears out of calibration,  
check calibration as follows.  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
2
3
USE SPECIAL SERVICE CO/ALR SOLDERLESS CONNECTORS  
WHEN CONNECTING ALUMINUM CONDUCTORS OR A FIRE  
HAZARD MAY RESULT.  
BREAKS AT POSITIVE OFF AND REMAKES UNDER –31°F (–35°C);  
NORMALLY THERMALLY ACTIVATED. BREAKS ON TEMPERATURE  
RISE; MAKES ON TEMPERATURE FALL.  
4
5
6
USE A SEPARATE LIMIT CONTROL IN THE HEATING APPLIANCE.  
BREAKS AT POSITIVE OFF ONLY; NOT THERMALLY ACTIVATED.  
DO NOT CONNECT GROUNDED CONDUCTOR (NEUTRAL) ON  
Check Calibration  
 Remove the thermostat cover and set it aside for  
several minutes because radiant heat from your hands  
will affect the thermometer reading.  
1
20 OR 227V CIRCUITS. INSULATE AND TAPE OR CUT OFF  
RED WIRES IF UNUSED.  
M5792B  
Fig. 3.Typical wiring connections for T4398B.  
 Turn the setting dial clockwise until the switch makes  
(click sound). The heating equipment and fan start.  
 No recalibration is necessary if the thermostat switch  
makes with the thermostat setting at the same  
temperature as indicated on the thermostat cover  
thermometer.  
68-0147—2  
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T4398A,B HIGH PERFORMANCE ELECTRIC HEAT THERMOSTATS  
BACK OF  
THERMOSTAT  
COVER  
 If the thermostat setting differs from the thermometer,  
record the temperature difference and recalibrate as  
instructed in the Recalibration Procedure section.  
Recalibration Procedure  
 Note the temperature difference between the  
thermostat setting and the thermometer.  
 Turn the setting dial clockwise until the switch makes  
INSERT RANGE  
STOP PINS IN  
SLOTS.  
(click sound).  
 Firmly hold the setting dial with one hand. Using the  
other hand, turn the outer scale ring counterclockwise  
until the 12 o’clock position of the scale ring is the same  
temperature as the cover thermometer. See Fig. 5.  
 Wait five minutes and recheck the calibration.  
THERMOSTAT  
BASE  
M5801  
Fig. 6. Setting range stops.  
THERMOSTAT BASE  
SETTING KNOB  
AT 12 O'CLOCK  
POSITION  
SCALE RING  
LOCKING  
COVER  
CLIP  
THERMOSTAT  
COVER  
SETTING KNOB  
M5796  
Fig. 5. Calibrating thermostat.  
LOCKING  
COVER SCREW  
Setting Range Stops  
Use the range stops, included, to limit the maximum and  
minimum temperatures that may be set.  
ALLEN WRENCH  
M5798  
Fig. 7. Locking cover.  
 Move the thermostat setting dial to the desired  
maximum temperature.  
 Remove the thermostat cover.  
CHECKOUT  
 Insert the range stop pins in the desired minimum and  
maximum temperature setting positions on the back of  
the thermostat cover. See Fig. 6.  
 Make sure the pins are completely seated before  
replacing the thermostat cover.  
IMPORTANT  
Make sure that all wiring connections are secure  
before beginning checkout.  
 Replace the thermostat cover and check the range stops.  
After thermostat installation is complete, check the operation  
as follows:  
Locking Cover  
 Move the thermostat setting knob clockwise until the  
switch makes (click sound); the electric heater starts.  
 Move the setting knob counterclockwise all the way; the  
switch breaks and the electric heater starts to cool.  
 Allow the thermostat to operate for several hours to  
determine the appropriate temperature setting. Adjust  
the setting as necessary. The precise temperature  
control of the T4398 allows the user to select a lower  
temperature setting, which saves energy while  
maintaining comfort.  
The thermostat cover may be locked using the locking cover  
screws included. Locking the cover prevents unauthorized  
tampering of the thermostat temperature setting.  
 Remove the thermostat cover.  
 Insert the locking cover clip (included) into the slot at  
the back of thermostat base as shown in Fig. 7.  
 Using the Allen wrench, insert the locking cover screw  
into the clip. Secure the screw in place until it is flush  
with the thermostat base.  
5
68-0147—2  
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T4398A,B HIGH PERFORMANCE ELECTRIC HEAT THERMOSTATS  
OPERATION  
The T4398 Thermostat provides precise temperature control  
of resistance-rated electric baseboard heating equipment with  
minimum droop. The T4398 controls room temperature within  
2°F (1°C), regardless of the load of the baseboard heater.  
The vapor-filled dual diaphragm sensing element is more  
sensitive to temperature changes than a bimetal sensor. This  
accuracy, usually associated with low voltage thermostats, is  
now available for line voltage control.  
Electric heat thermostats are often affected by the heat  
generated in the control. Temperature control points can vary  
or droop 2° to 4°F (1° to 3°C) depending on the load demand.  
Temperature settings are adjusted to offset this. The T4398  
provides precise control with minimum droop. This allows  
better control of room temperatures from day to night and  
season to season while saving energy.  
68-0147—2  
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68-0147—2  
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Home and Building Control  
Honeywell Inc.  
Home and Building Control  
Honeywell Limited-Honeywell Limitée  
155 Gordon Baker Road  
North York, Ontario  
Helping You Control Your World  
1
985 Douglas Drive North  
Golden Valley, MN 55422  
M2H 2C9  
Printed on recycled paper containing at  
least 10% post-consumer paper fibers.  
68-0147—2 C.H. Rev. 4-96 Printed in U.S.A.  
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