About Thermostats

How to Select a Thermostat

There was a time when it seemed nearly all thermostats were the basic round Honeywell-style thermostats. Today there are lots of choices. Low voltage thermostats are used for oil and natural gas-fired heating systems and systems with central air conditioning. Line voltage thermostats are used in conjunction with electric resistance heating systems. The thermostats offered are all low voltage thermostats, but following is information to help you determine whether a conventional programable thermostat or a Wi-Fi enabled communicating thermostat is right for you.

Programmable Thermostats

Thermostats in this category are also called setback thermostats, allowing the user to set the temperature based on the day of the week and the time of the day. Most programmable thermostats allow for four settings per period, allowing a residential user, for instance, to have one setting early in the morning, a second once everyone has left the house, a third for when people return home, and a fourth once everyone has gone to bed. There are two types:

  • 5-2 Day Thermostats: Supporting one schedule for Monday-Friday, and a second schedule for the weekend.
  • 7 Day Thermostats: Supporting a different schedule for each day of the week.

These types of thermostats can generally be installed as direct replacements for common low voltage non-programmable thermostats with no wiring changes. If no Wi-Fi is available at the location, these thermostats can deliver reliable savings if programmed appropriately.

Wi-Fi Enabled Thermostats

Wi-Fi enabled thermostats are "smart thermostats."

Because they are Wi-Fi enabled, they may be controlled wirelessly, allowing the user to adjust the set points through a device such as a smart phone.

Many models go beyond that, being analytics capable, which means they offer the ability to drive additional energy savings through remotely-driven adjustments that can improve the efficiency of the heating/cooling system. Some manufacturers also offer:

  • E-mail communications through which the user can better understand their energy use,
  • Occupancy-sensing/geofencing functionality (allowing the "away" setting to be activated when the building is unoccupied),
  • Automatically adjusting the thermostat settings based on user behavior,
  • Factoring in weather-related data to improve savings over time, and/or
  • Allowing the thermostats to interact with other Wi-Fi enabled devices in the home.

While smart thermostats include do-it-yourself instructions and are straightforward to install, these thermostats need a continuous supply of 24 volt power, usually delivered through a wire known as a "C" wire. This common wire delivers uninterrupted low voltage power to illuminate the display and allow the thermostat to be available for communication from other wireless devices and smart phones. When the existing thermostat is removed, there is likely to be a connection terminal labeled "C", which is the terminal the "C" wire would be connected to. If the "C" wire is not there, and not tucked behind the thermostat in the wall, a 18/5 wire will usually need to be run from the heating system to the thermostat. This can be done by an HVAC technician.