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.

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.

The number days per week that the thermostat will be able to individually program. Ex. a 5,1,1 programmable thermostat will have the same program settings on Monday-Friday and will be able to individualize the programming on Saturday and Sunday. A 7 day programmable thermostat will be able to set a different programming schedule for each day of the week.

Indicates that this thermostat is compatible with heat pumps.

The minimum and maximum temperatures on the thermostat.

Resilient Mounting - Sometimes called rubber or hub mounted - motor shell is isolated from base by vibration absorbing material, such as rubber rings on the end shields, to reduce transmission of vibration to the housing of the unit or appliance. Stud Mounting - Motor has bolts extending from from front or rear, by which it is mounted. Often used on small, direct drive fans and blowers.

Indicates that this thermostat can be used with either a gas furnace or oil furnace.

Indicates that this thermostat is compatible with electric furnaces or air handlers with electric heater coils. The voltage to the thermostat will be the normal 24 VAC. This feature is different from a "Line Voltage Capable" thermostat which operates with 120 to 240 VAC.

Allows for you to establish by schedule when you want your furnace/air handler fan to turn on and off automatically to circulate home air, even without your furnace or air conditioner operating.

This feature allows the thermostat to automatically switch from heating to cooling based on the temperature inside. This is useful between seasons when heating may be needed at night, and cooling during the day.

Will operate on 120 volts A/C or 240 volts A/C as indicated for that model. Electric baseboard and specialty heaters often require a line voltage capable thermostat.