Thermostat Settings: Summer, Winter, Fan

What the mode and setpoint settings mean

A setpoint is the temperature you ask the thermostat to hold. A setback is a planned move of that setpoint, down in winter or up in summer, for hours when you are asleep or away.

The Honeywell Home ElitePRO manual lists four system modes: Heat, Cool, Off and Auto. In its words, Heat controls only the heating system, Cool controls only the cooling system, and Auto selects heating or cooling depending on the indoor temperature. Sensi, another maker, says its Auto mode lets the thermostat switch from heat to cool, or cool to heat, using one heating setpoint and one cooling setpoint. Sensi says it keeps the two setpoints at least two degrees apart, so that heating and cooling do not run at the same time. Our reading: on a mild day, an Auto thermostat with its two setpoints close together can switch between heating and cooling, and a wider gap between them avoids that.

For heat pumps, the Honeywell Home manual lists a fifth mode, Em Heat, which it says controls emergency heat with the compressor locked out. The manual adds that the modes you see can vary with your system type and the installer settings. What emergency heat does, and when it is used, is covered in what is emergency heat. How a thermostat decides when to start and stop the equipment is covered in how a thermostat works.

Cooling: where the 78°F figure comes from

UF/IFAS Extension's air conditioning guide for Florida homes lists setting your thermostat at 78°F or higher among the short-term steps it attributes to the Department of Energy. ENERGY STAR's 2009 heating and cooling guide offers a table of settings as a starting point, with cooling settings above 78°F in the morning and evening periods. Tampa Electric's hot weather tips, dated June 18, 2026, say that setting the thermostat to 78°F while you are home is a sweet spot. A Carrier consumer page dated September 30, 2026 recommends starting at 78°F in summer while you are home and awake.

The Department of Energy's 2022 Energy Saver Guide words the summer advice as a comfort limit. It says to set the thermostat as high as is comfortable when you are home and awake, and to raise it when you are sleeping or away. Our reading: every source treats 78°F as a place to begin, and each leaves room to adjust for comfort. Our reading: if the house feels clammy at 78°F, a lower number may only hide the cause.

Heating: starting points below 70°F

ENERGY STAR's 2009 table has heating settings below 70°F in its morning and evening periods, with a setback of at least 8°F in the daytime and sleep periods. The Department of Energy's 2021 consumer guide says to keep thermostats at the lowest comfortable temperature when you are awake, and to set them back further while you sleep. Carrier's page starts at 68°F in winter while you are awake and at home, and suggests changing it by 1 or 2 degrees at a time.

Our reading: the sources start just below 70°F and share one idea, the lowest setting that still feels comfortable. Which heating system you have decides what a winter setting does. Heat pump vs furnace and gas furnace vs electric strip heat compare the systems, and when to turn on your heat covers the start of the heating season.

Heat pump settings in winter

Backup heat for a heat pump is covered in what is auxiliary heat. The Department of Energy's current Home Upgrades page says programmable thermostats have generally not been recommended for heat pump systems. It adds that some companies have begun selling programmable thermostats made for heat pumps. ENERGY STAR's 2009 guide also says a heat pump may require a special programmable thermostat, and to talk to your retailer or contractor for details.

A Building America Solution Center guide says a heat pump's programmable thermostat should have adaptive-recovery technology. It explains that this technology directs the heat pump to minimize the use of auxiliary heating when returning the space from a set-back temperature to the desired temperature. Its example sets the temperature back to 62°F during a winter workday and returns it to 68°F at 5 pm. In the afternoon, the thermostat starts the heat pump earlier, which lets the heat pump alone raise the temperature gradually over a longer period.

Carrier's page says a heat pump owner should follow the setback recommendations for the specific system and thermostat, rather than automatically applying a 7 to 10°F setback. Our reading: for a heat pump, the two questions that matter are whether the thermostat is made for heat pumps and what it does about backup heat. Our reading: a thermostat that is not made for heat pumps may bring on backup heat when it recovers from a setback, so ask before you program one.

The fan setting: Auto, On and Circulate

The Honeywell Home help page lists three fan modes. In Auto, the fan runs only when the heating or cooling system is on. In On, the fan is always on. In Circ, short for circulate, the fan runs about a third of the time. A second Honeywell Home page says Circ is normally used when seasonal demand is low, such as fall or spring, or during a setback.

The Department of Energy's 2022 Energy Saver Guide says to set the fan switch to Auto unless an indoor air quality professional has set up the system to run continuously for health reasons. Our reading: On has real uses, such as keeping air moving, and the Department of Energy leaves room for them when a professional sets the system up that way.

What the research says about fan On in a humid climate

A Florida Solar Energy Center report from January 1987 compared fan Auto with fan On on two air conditioners. It found that net moisture removal was reduced significantly when the fan ran continuously, compared with when the fan cycled off with the compressor. In one 20-minute cycle on a packaged terminal air conditioner, the compressor ran for 10 minutes and then the fan ran alone for 10 minutes. In that cycle, nearly a fifth of the moisture that condensed while the compressor ran was re-evaporated back into the conditioned space. Our reading: the one-fifth figure describes moisture, not energy or money, and it comes from a 1987 test of two machines, not from a Tampa Bay house. Our reading: the report tested only Auto and On, so it does not say how much a Circ mode would re-evaporate.

The National Weather Service Tampa Bay Area links the summer rainy season to a rise in humidity. Our reading: on those humid days, a running fan has more moisture to carry back into the house. For why a house can stay humid with the AC running, see why your house feels humid with the AC running.

A Building America Solution Center page on air handler fans describes electronically commutated motors, or ECMs, as variable speed. It says ECM fans use about 400 watts in cooling mode and about 80 in continuous fan mode. It says a single-speed permanent split capacitor, or PSC, motor typically consumes between 500 and 550 watts when providing heating and cooling. Our reading: a single-speed motor probably draws near that figure whenever it runs, so leaving the fan On uses more electricity with a PSC motor than with an ECM.

The same page describes one control scheme for ECM motors in a wet climate, with the fan going off at the end of the compressor cycle to allow the coil to drain. The page adds that, even when the system is set to constant fan, the fan still shuts down for 20 minutes at the end of the compressor cycle so the coil can drain. Our reading: whether your air handler does that depends on its controls, and the label on the thermostat cannot tell you.

Do room fans help the air conditioner?

The thermostat's fan setting is not the same as a ceiling or box fan in a room. The thermostat setting runs the air handler's blower through the ducts, while a room fan only moves the air in one room. The Department of Energy's 2022 guide says ceiling fans cool by creating a wind chill effect and can allow you to turn up the thermostat a few degrees. It gives about 4°F as the amount you can turn the thermostat up without any loss in comfort. It also says to turn off ceiling fans when you leave a room. Tampa Electric says fans do not lower room temperatures but make you feel cooler, and that fans cool people, not rooms. Our reading: a fan changes how the moving air feels on your skin and not the air temperature, so it helps when someone is in the room and does nothing for an empty one.

Questions to settle before you change the settings

1. What kind of heat do I have? A heat pump, a furnace and electric strip heat are different systems, so the same winter number may do different things.
2. If it is a heat pump, is the thermostat made for one? Ask what it does about backup heat before you set a temperature back.
3. Is the fan on Auto? If it is On, find out who set it that way and why.
4. Does my air handler have an ECM or a PSC blower motor? The equipment literature or a licensed contractor can say, and the answer affects what the On setting uses.
5. Is the problem temperature or humidity? If the house is clammy at 78°F, see why your house feels humid with the AC running before lowering the number.
6. How far apart are my heat and cool setpoints in Auto mode? A close gap can make the system switch between heating and cooling.

Changing a setting on the thermostat's screen or app is something you can do yourself. The wiring behind the thermostat and the equipment cabinets are work for a licensed contractor. A thermostat that reads wrong or acts oddly is covered in signs a thermostat is going bad.