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Actual product may vary from photos.
The Honeywell THM5421C1008 has been discontinued.
Please call us for a suitable alternate product.

(800) 865-5931

Mon-Fri 8am-7pm, Sat 9am-3pm CT

Premier white Honeywell VisionPro IAQ TH9421 equipment interface module, with up to 4 stages of heat and 2 stages of cool.  The thermostat connects to this equipment interface module to control temperature, humidification, dehumidification and ventilation from a single point in the home.

  • Thermostat and equipment interface module work together to control temperature, humidification, dehumidification, and ventilation from one location
  • Electrical range: 20 to 30VAC

Stages of Heat

The number of terminals on the thermostat that can be used to individually control separate heating functions. Many furnaces that are called two stage heaters will require at least a two stage thermostat to operate appropriately. You may also choose a multiple stage thermostat when pairing different heating equipment. Such as a heat pump and a furnace.

Stages of Heat
Stages of Cool

The number of terminals on the thermostat that can be used to individually control separate cooling functions. Some of the higher efficiency air conditioners and heat pumps are designed to use multiple stages of cooling.

Stages of Cool
Power Method

Indicates if the thermostat operates electrically on batteries or power from the furnace/air handler.

Power Method
Premier White
4 1/2 Inches
1 3/8 Inches
7 1/4 Inches

In 2002 Alpine Home Air Products became the first company to sell heating, air conditioning and indoor air-quality products online. We have proudly served hundreds of thousands of customers, helping them save time and money by buying their products direct.