PexSupply, the online leader in plumbing supplies and heating supplies, provides a helpful thermostat buying guide.

1. Thermostat Buying Guide
There are many factors to take into consideration when purchasing a
thermostat. This guide will discuss key differences between
thermostats and how to decide which thermostat is right for you. The
main differences between thermostats are:
 Number of Stages
 Programmability
 Application
 Brand
 User Interface
 Features
 Color
 Mount Type
 Voltage
 Changeover Type
Stages
The number of stages refers to the number of heating or cooling
sources that may be controlled by a single thermostat. For example, if a
system contains baseboard heat, a hot air system, and air conditioning
then there are two heating stages, and one cool. In this example, a
thermostat that can control two heat sources and one cool source
should be selected. It is important to note that if you have auxiliary
heat (or backup heat), that counts as a second heating source.
Number of stages may be written in several different ways. The two
most common are 2H/1C or 2 Heat / 1 Cool. These mean the same
thing-- that there are two sources of heat and one source of cool that
may be controlled by this thermostat. Number of stages can vary from
single heat or single cool all the way up to 4 Heats and 3 Cools on one
thermostat. In order for the wiring to work properly, you must

2. purchase a thermostat that accounts for the number of heating or
cooling sources present in your given space.
Programmability
Programmability refers to the level of control a user can have over the
system. Programmable thermostats allow you to set the heating or
cooling system to turn on or off at certain times of the day or on certain
days of the week at different temperatures. A 7-day programmable
thermostat may have a distinct time and temperature setting for each
day of the week. Other common types of programmable thermostats
include the 5-2 and 5-1-1 which allow one weekday setting and one (for
the 5-2) or two (for the 5-1-1) separate settings for the weekend when
the hours spent in that room will likely be different.
A non-programmable thermostat's settings must be manually changed
for temperature and on/off functionality of heating or cooling sources.
Due to the level of control with a programmable thermostat, these
units are highly energy efficient and allow you to save money on
heating and cooling bills. For example, if no one will be in a given space
from 9am to 5pm, a programmable thermostat can be set to turn off at
9 am and turn back on at 4.30pm so the space reaches a comfortable
temperature for when you return. In contrast, a non-programmable
thermostat may either be left on during this time period, wasting
energy and money, or off, meaning that you get home to an
uncomfortably hot or cold room.
Application
Thermostats vary by the different types of heating and/or cooling
applications they control. Because there are many different heating and
cooling sources it is important to make sure the thermostat you
purchase can operate the type of heat or cool source you will be using.

3. For example, some thermostats can handle a heat pump system while
others cannot. If you have a heat pump system, it is important to
purchase a thermostat that specifically states that it can be used with a
heat pump system or your thermostat will not work properly. The same
logic applies for electric heat, millivolt, and other systems.
User Interface
User interface refers to the way in which a person interacts with their
thermostat. Thermostats may be mechanical with a simple dial, digital
with buttons to move the temperature up or down, or feature a touch
screen. As thermostats move from mechanical to touch screen, they
tend to get more complicated in terms of functionality and operation.
Touch screen thermostats are relatively new, but are quickly gaining in
popularity. An example of a touch screen thermostat is the Honeywell
TH8110U1003.
Features
Some thermostats offer features that are specific to that thermostat.
These features may include sensors (indoor, outdoor, remote...),
humidification control, and password protection. If you need one of
these features, be sure to check the product description to see if it
contains the given feature.
Color
Thermostats can vary in color. The most common color for thermostats
is white, but many thermostats are off-white and other colors may be
found.

4. Mount Type
Thermostats may be mounted horizontally or vertically. This is generally
decided based on either a preference in the way the thermostat looks
or space constraints. Several models of thermostats may be purchased
in vertical or horizontal mount.
Voltage
Thermostats run on either line voltage or low voltage. The easiest way
to tell if you need a line or low voltage thermostat is to look at the wire.
If it's a very thin wire (like a doorbell or speaker wire), you'll need a low
voltage thermostat. If it's a heavy wire, you'll need a line voltage
thermostat.
Changeover Type
Thermostats may feature automatic changeover or manual changeover.
Changeover refers to the thermostat being switched from heat to cool
as the air crosses a certain temperature. Auto changeover thermostats
switch from heat to cool automatically while manual changeover
thermostats must be changed by hand.
There are several manufacturers of thermostats available to consumers
today including Honeywell, White Rodgers, Robertshaw, Lux, Wirsbo,
and Tekmar.
While Honeywell thermostats are the most recognized and the best-
selling brand of thermostat, all of these manufacturers are large
companies that produce high-quality products and stand behind them.