Honeywell T8635L Thermostat User Manual

Honeywell T8635L Thermostat User Manual

USING THIS Honeywell T8635L Manual

The T8635L is a multi-functional thermostat. This means it can be used in several different ways such as single or multi-zone applications, conventional furnaces or heat pump equipment.

The following symbols will help you identify the features that apply to your system:

  • Triple layer of thermostats with the word, zoning, below. These features are available when more than one thermostat is connected and used with the optional W8703 Damper Interface Module.
  • Compressor with the word, heat pump, below. These features are available when used with a heat pump with auxiliary heat.
  • Tip symbol. Look for helpful tips throughout the guide when you see this symbol.

Honeywell T8635L FEATURES

  • Adaptive Intelligent Recovery™ Control for comfort and energy savings.
  • Customize the program schedule—program your own schedule to fit your needs.
  • Temporary schedule override—set the thermostat higher or lower for the current program schedule.
  • Permanent schedule override—set the thermostat higher or lower indefinitely.
  • Vacation mode (1 to 255 days) for added comfort and energy savings. Set the temperature higher or lower for energy savings while on vacation. At the same time, set the comfort level you want when you return.
  • Set the filter indicator (0, 15, 30, 60, 90, or 120 days) to remind you to change the filter.
  • Information at the press of a button—use the (information) key to see the outdoor temperature (C7089B Outdoor Temperature Sensor optional accessory), the current setpoints, or the filter status.
  • No batteries needed—your thermostat retains the schedule for the life of the product. You never have to reprogram the schedule even after a power outage. (You may need to reset the day and time after an extended power outage.)
  • Daylight Time key for quick time changes between Daylight and Standard time.
  • Backlit display for improved readability—set the backlight feature for backlighting on demand (press any key to activate) or continual backlighting. Ask your installer to program this feature.
  • Optional outdoor temperature display—ask your installer to install an outdoor temperature sensor to activate this feature.


Your new thermostat is so smart, it’s almost human. You perceive temperature from a variety of sources, not only from the air in the room, but also from your surrounding walls, windows and furnishings. Humans feel differences in temperature as slight as two degrees Fahrenheit. Common household thermometers and standard thermostats sense only air temperature, which may not reflect how hot or cold the room actually feels to you. Your new thermostat reads both the temperature of the wall and in the air, and responds to temperature changes as little as one degree Fahrenheit, so room temperature is more likely to feel right to you and your family.

The thermostat acts like a computer. When calculating the time to turn on your heating or cooling system, it considers air temperature, wall temperature, and the time you want to reach the comfort temperature. After considering these three things, Adaptive Intelligent Recovery™ control gradually changes the temperature from the energy savings setting to the comfort setting (for example, from a heating temperature of 62° at night to 70° in the morning).

The system runs continuously until the comfort temperature you choose is reached without overshooting the setting. This saves energy. How do you know when the system is in recovery? The thermostat displays “Recovery” whenever the thermostat activates Adaptive Intelligent Recovery™ control. See Fig. 3. So, “Recovery” displays during the recovery time from Sleep to Wake and from Leave to Return.

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Honeywell T8635L Manual

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