1. Decide whether you’re interested in a non-connected programmable thermostat or a smart thermostat.

If all you care about is simple programming, a non-connected thermostat will suffice, and these models are much more affordable. If you’re interested in controlling your thermostat with your voice or an app, or letting it learn your habits and adjust the temperature accordingly, then you should consider a smart thermostat. To narrow your choices, factor in smart features (such as geofencing), price, and attributes that matter to you, such as color, size, or style.

2. Consider your HVAC system.

Nearly all of our tested models work on common heating and cooling systems, but check the packaging for exceptions. This is especially a concern with smart thermostats, because not all models support all types of HVAC systems. For example, the Nest Thermostat E doesn’t support two-stage heat pump systems, but the Nest Learning Thermostat does. And if you have separate heating and cooling systems, you may need to install a separate thermostat for each system, as well as for each zone of heating and cooling.

3. Scope out your wiring.

You’ll also want to open up your existing thermostat to see what kind of wiring you have. Most non-connected, programmable thermostats will work with as few as two low-voltage wires (common in older heating systems), but newer thermostats often require a common wire, or C-wire. The C-wire provides continuous power for features like displays and WiFi. If you aren’t sure whether you have a C-wire, you’ll need to consult an HVAC technician.

If you know you don’t have a C-wire but you really want a smart thermostat, you have a few options:

• Choose a model with a power adapter or power extender that allows you to add a C-wire to your system, such as those from Ecobee and Honeywell Home.

• Buy and install a third-party add-a-wire adapter.

• Pick a model from our ratings that doesn’t require a C-wire (look under the Features & Specs tab in our ratings table). Both Nest and Emerson claim you don’t need a C-wire for many systems. Nest models, in particular, have an internal battery that charges whenever your system is running. But some HVAC professionals caution against this arrangement, saying it could potentially damage your HVAC system.

• Have a C-wire professionally installed.

4. Consider your home’s aesthetics.

If you’re replacing something that will stay on your home’s wall for the next decade, you’ll probably want it to look good. Today’s thermostats, especially smart models, come in a variety of shapes and styles. You could go for the classic, round look of Google Nest thermostats or the futuristic all-glass, rounded-square style of Ecobee models. Honeywell Home and Lennox thermostats offer a more modern, boxy look with large displays, and models from Emerson, Hunter, and Lux have a more conventional style that you’d expect from programmable thermostats. Of course, when it comes to looks, the decision is entirely up to you. You’re the one who’s going to have to live with it, so choose the style that looks best in your home.

A Word About Installation

Most non-connected thermostats can be wired easily into your home’s heating and cooling system. Simply take a photo of the wired connection on your current thermostat so that you know which wires go where and connect those wires to the corresponding ports on your new thermostat. Many smart thermostats will also include detailed installation instructions or video walkthroughs to make the process easier. Consumer Reports also has a step-by-step installation guide and video to help you complete the task.

TIP: Install a thermostat on an interior wall that’s centrally located, and away from vents and other sources of drafts or direct sunlight, which could distort temperature readings.