March 1, 2018

A programmable thermostat, also known as a setback or clock thermostat, can be a simple way to save on utility costs while maintaining comfort in your home. However, figuring out how to program the thermostat so that it maximizes efficiency may be a bit confusing. This blog post can help you, the homeowner or renter, match your daily routine to your home's heating and/or cooling system to make a programmable thermostat work for you.

Heating/cooling systems and how they work with programmable thermostats

A forced air furnace and a hydronic heating system differ in the way that they heat a home. A forced air heating system uses ductwork to circulate and heat the air in a home. Hydronic heating systems use radiators and rely on the difference in temperatures from one object to another for the transfer of heat. Because of the difference in how these two types of systems distribute heat, the amount of degrees recommended for a home to cool down during a setback period is not the same. If a setback temperature causes a system to use more energy to reheat a home, it defeats the purpose of using a programmable thermostat.

For a forced air heating system, the difference from your comfort set point to the lower temperature you set your thermostat to (also known as the setback) can be a bit greater without using more energy than intended. For nighttime and away periods, a setback of 6°F to 10°F below your typical comfort temperature is recommended to save you the most energy while maintaining comfort. For example, if you keep your heat at 70°F when you're home, you could keep it at 60-64°F while you're asleep or away from your home.

With a hydronic heating system, the recommended setback temperature difference is no more than 4°F to 6°F below the comfort temperature your thermostat is set to when you are home. When all the furniture, floors, walls, and other items inside of a home cool down, it requires energy to warm all those solid objects back up to your comfort level. For this reason, the best setback temperature is not as great as it is if you have a forced air furnace. To continue using the above example, if you keep your heat at 70°F when you're home, you should keep it at 64-66°F while you're asleep or away from your home.

Ways that programmable thermostats help out

A so-called “adaptive intelligent recovery” programmable thermostat can help a heating system avoid overheating or cooling down too much. This is a specific type of technology that can learn the routine of people in a home. Ask your HVAC technicians about their recommendations on the best options to suit your lifestyle and your heating and cooling system type.

Programmable thermostats can also reduce electric use by allowing an unoccupied home to warm during the summer cooling season. An air conditioning technician can assist with the programming of cooling setback temperatures and ensure that the humidity level is properly maintained for comfort. Keep in mind that some systems, such as heat pumps and electric baseboards, often do not benefit from the use of programmable thermostats.

How to set a programmable thermostat

How your programmable thermostat works is all up to you. The times of day to program a setback in temperature are when you are in bed for the night and when your house is unoccupied. However, the time of the setback will be different for everyone. Some people want the house to start cooling down before they leave their home or go to bed, while others would prefer the setback to match their schedule exactly.

There are 7-day programmable thermostats, which can have different time settings for each day of the week. There are also 5-day/2-day programmable thermostats that allow for consistent weekday time settings, as well as separate weekend settings. With the options available, there is certain to be one that fits your needs for comfort and helps you achieve energy savings.

Finally, many digital thermostats have a degree differential setting which designates when a system turns on and off. This setting will control how much the temperature in a home changes before a call for heat or cooling starts a system. Most thermostats will turn on a system at a temperature change of 1°F.

Digital thermostats have an adjustment that can change how often a system cycles and, in turn, save on energy use while maintaining comfort. When the thermostat differential setting is changed to 2°F instead of 1°F, the system will run less often, and you won’t experience a difference in comfort; the human body tends not to notice a temperature change until it exceeds 2°F. A differential setting needs to be considered as part of the setback total when programming the thermostat.

A programmable thermostat is a great start to introducing energy efficiency to your home. And, this small investment will quickly pay for itself. Find a BPI GoldStar Contractor or BPI Certified Professional to help you decide on, or program, your thermostat.

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Jeremy O'Brien

Jeremy O'Brien joined the Building Performance Institute, Inc. team in 2009 and currently works as a Technical Relations Representative. Jeremy has worked in the home performance industry for 18 years and has had many roles such as energy auditor, air sealer, insulator and more. At BPI, his duties include completing quality assurance inspections, proctoring exams, assisting with exam and standards development and providing responses to technical questions on the website.