T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
Ambient Temperature Range: 40°F (4°C) to 110°F (43°C).
The specifications given in this publication do not
include normal manufacturing tolerances; therefore,
an individual unit might not exactly match the listed
specifications. Also, this product is tested and cali-
brated under closely controlled conditions, and some
minor differences in performance can be expected if
those conditions are changed.
Shipping Temperature Range: -20°F (-29°C) to 120°F
Operating Relative Humidity: 5% to 90% RH, non-
Cycle Rates (at 50% Load):
T8400C, T8401C, T8424C,D TRADELINE® models include a
thermostat, wallplate for wiring and mounting thermostat and
Heating: Selectable at 1, 3, 4, 5, 6, 9 or 12 cph. See Table
1 for cycle rate options and corresponding system
Cooling: Fixed at 3 cph.
T8400C, T8401C SUPER TRADELINE® models include a
thermostat, wallplate (for mounting and wiring thermostat),
two decorator cover plates for covering wall marks (3-7/8 in. x
Table 1. Heating Cycle Rates.
Cycles Per Hour
-7/8 in. and 5-3/4 in x 5-3/4 in.), and owner’s guide.
Hydronic heat, condensing
T8400C: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
T8401C: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
T8424C,D: 24 Vac nominal, 18 to 30 Vac, 50/60 Hz.
Gas or oil forced air (default)
Heating: .02 to 1.5A run; 3.5A inrush.
Cooling: .02 to 1.5A run; 7.5A inrush.
Fan: .02 to 0.5A run; 2.5A inrush.
High efficiency furnace.
Refer to equipment manufacturer’s instructions.
T8400C Power Stealing Thermostat requires less than
.25 mA current draw when the thermostat calls for heat
and is compatible with most 24V microprocessor systems.
The T8400C Power Stealing Thermostat can be used in
any non-millivolt application where the T8401C and
T8424C,D Hard Wired Thermostats cannot be used. For
further detail, see Power Stealing in the Operation section.
T8400C, T8401C and T8424C,D TRADELINE® AND SUPER
TRADELINE®: Taupe finish.
T8400C, T8401C and T8424C,D STANDARD MODELS:
Premier White® finish and only available in builder packs of
Setpoint temperature is adjusted by using the ▲ or ▲
keys. One press changes the setpoint one degree; press-
ing and holding changes the setpoint several degrees.
Accessory: Decorator cover plates (for covering wall marks):
-3/4 in. x 5-3/4 in. and 3-7/8 in. x 3-7/8 in.
Dimensions: See Fig. 1 or 2.
Temperature Setting Range: 40°F (4°C) to 99°F (37°C).
When purchasing replacement and modernization products from your TRADELINE® wholesaler or distributor, refer to the
TRADELINE® Catalog or price sheets for complete ordering number.
If you have additional questions, need further information, or would like to comment on our products or services, please write or
Your local Home and Building Control Sales Office (check white pages of your phone directory).
Home and Building Control Customer Relations
Honeywell, 1985 Douglas Drive North
Golden Valley, Minnesota 55422 (800) 468-1502
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.