This Thermostat Mistake Is Straining Your HVAC Units

If you’re setting your upstairs and downstairs thermostats to the same temperature, then you might be overworking your HVAC system and wasting money. The physics of air flow means it makes more sense to set the upstairs and downstairs thermostats to different levels. We sought out Michael Morey, Smart Thermostat & Home Product Manager at Trane, to explain why.

How Should I Set My Thermostats?

The problem with setting your upstairs and downstairs thermostats to the same temperature has to do with how warm air and cold air travel in your home. Warm air goes up into the higher parts of your home while cold air settles to the bottom. Thus your upstairs HVAC unit works harder to keep your home cool in the summer, while the downstairs unit works harder to keep the floor warmer in the winter. By setting the thermostats to different temperatures you can offset the workload, Morey says.  

He recommends setting the upstairs thermostat 2 to 3 degrees warmer than the downstairs thermostat in the winter and 2 to 3 degrees cooler than the downstairs in the summer. “This is because heat naturally rises so doing this can compensate for natural temperature differences between floors while ensuring each floor is comfortable without overworking the HVAC units,” he says. 

How Does Staggering Your Thermostats Save Your HVAC System? 

Setting the upstairs cooler in the summer creates what’s called the cascade effect. The upstairs unit does the brunt of the work in the summer, creating cool air that cascades to to help cool the downstairs, so your downstairs HVAC doesn’t have to work as hard. This helps to prevent short cycling, which is when your AC turns off and on too quickly, damaging the compressor. 

In winter, hot air rises, helping to warm the upstairs. By setting your upstairs thermostat two degrees colder in the winter, the upstairs heating unit doesn’t have to work as hard, resulting in less wear and tear. 

How Should I Set My Thermostats?

While Morey recommends setting your thermostat to suit your personal comfort levels, there are guidelines if you want to balance comfort and efficiency. He recommends following the Department of Energy recommendation, which is to set your thermostat to 68℉ in the winter. If you have a two zone thermostat, that means setting the first floor to 68℉ and the second floor to 66℉. 

In the summer, the Department of Energy recommends setting your thermostat to 78℉, which means setting your first floor thermostat to 80℉ and your second floor thermostat to 78℉. Following these guidelines can save you up to 10% in energy costs each year, according to the Department of Energy.

Morey adds that while following these guidelines can save you money, personal comfort should also factor in. “The optimal thermostat setting on each floor depends heavily on your personal comfort levels and overall living habits,” he says. 

Related: How Often Should You Change Your HVAC Filter and Which One Is Best for Your Home?

FAQs

Can I turn off one thermostat to save money?

While you might be tempted to go extreme by turning a thermostat on an unused floor off or way back on an unused floor, don’t. Doing so can cause the HVAC system on another floor to run extra long, increasing its wear tear while not saving you an additional money in energy costs. 

How do I set a thermostat on a three story home?

If you have a thermostat on each floor, set each one so that it’s one degree apart. For example, in the summer you might set the first floor to 80℉, the second floor to 79℉, and the third floor to 78℉