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7 July 2021

How we test smart thermostats

Find out how we test smart thermostats in the Which? lab, and what a smart thermostat has to do well to be rated as a Best Buy.
Matt Clear
Honeywell smart thermostat

Our tests reveal the very best and worst smart thermostats, based on how easy they are to use, how well they function and the features that they offer.

Video: what makes a Best Buy smart thermostat

To see how all smart thermostats our experts have reviewed fared across our independent lab tests, go to our full list of smart thermostat reviews.

Is it easy to set up and connect to your wi-fi?

Whether you need a professional to install your smart thermostat or whether you can do it yourself, we assess how straightforward the process is and how useful the instructions are. We also connect the devices to wi-fi, penalising devices that require a really long or complicated setup.

Is it easy to adjust settings and program schedules?

Once it’s set up, you want to be sure that your smart thermostat is easy to live with. We judge how easily you can program your schedule through the app, the web portal (if there is one) and the device itself, so you can be sure to have a variety of user-friendly interfaces.

Does it have a wide range of features?

Some smart thermostats come with a range of features that make life easier, such as a child lock for safeguarding your settings, frost protection to stop your pipes freezing and a handy touchscreen display on the unit. Our reviews run through all the features of each smart thermostat so you can make sure you buy one that meets your needs.

How well does it function?

You expect your smart thermostat to be accurate, so we put each model through its paces to see exactly how precise it is. We put smart thermostats in a temperature-controlled chamber, measuring how accurately they record the temperature, and how long it takes for them to trigger the relay after the temperature drops below the selected threshold.

How secure is the connection?

Privacy is vitally important with a smart thermostat. Data in the wrong hands could show when you’re likely to be out of the house, leaving your home vulnerable to a robbery. Our thorough tests make sure that each smart thermostat meets the standards we expect for preventing potential data breaches.

Should you buy a smart thermostat?

We answer this question by combining our Which? lab test results into a total test score for smart thermostats that tell you how good it is overall.

Our total test score ignores price and is based on:

  • 50% ease of use
  • 40% thermostat function
  • 10% features

Smart thermostats with a total test score of 70% or above earn our Best Buy recommendation.