In the house, why does heat set at 68 feel different than ac set on 68? It’s the same temperature but they feel very different!
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The temp you set is the goal temp to get the air to. You don’t get 68 degrees by generating 68 degree air. For heat, you blast 100 degree air to mix with the existing ambient air until they mix to reach 68 degrees and then the furnace shuts off. And when you want to cool a room to 68 degrees, the AC blasts 40 degree air which mixes with the air in the room until the combined temp is 68 and then the AC shuts down. But there will be hot or cold spots in the room, especially in proximity to your vents, so you may feel more of the cold AC air or hot furnace air in spots until it mixes adequately.
Worked in AC business for 16 years, the difference is based on where your thermostat is compared to where you are “feeling” the temperature difference. When your AC turns on there are only two things that change on most modern AC units.
1: the compressor or the heating element is on or off
2: fan speed (even this is for units less than 10 years old)
When your Air conditioner is told by the thermostat “it’s cold, we need heat” it turns the heating to on and the fan to on. No matter what that heat is at 100% and it’s forcing air through the duct to the different rooms. So if you are in your bedroom with the heat on it is actually a bit hotter than if you were standing next to the thermostat because heat takes some time to travel and the thermostat takes time to recognize its at the correct temp. And for cooling the opposite happens, cooler Temps further from t-stat. Also as mentioned before the humidity is a factor as well. Heating a house does not remove humidity while cooling does.
Edit to add: this is how most residential AC systems work, there are some that are smarter and have a few more bells and whistles that try to even it out but usually come with a premium cost and maintenance so I didn’t delve into those systems.
At the heart of those systems the above still applies generally. If your interested in some of those let me know and I’ll delve deeper.
Others have mentioned humidity which can definitely make a difference.
Another big difference is from radiant heat. On a hot day, the heat not only warms up the air, but also the walls of your home as well, and those walls radiate heat back inside. Your body absorbs radiant heat much more readily, thus why you can feel warm by a campfire on a cold evening. Your standard thermostat can’t accurately account for radiant heat, so even though the air temperature may be the same, you’ll feel warmer on hot days as the walls warm you up.
It’s probably several differences reasons and I can think of three.
1. Humidity plays a big part in how the air feels. If you’re heating to 68 then it’s likely winter time and humidity is low. If you’re cooling to 68 then it’s summer and humidity is high (though the AC does pull water from the air, it could very well still be wetter than winter air.
2. Depending on the current season, 68 can feel cold or warm because you’re more accustom to the current outside temp. In the winter, 68 feels warm compared to the outside temperature and you’re likely wearing more clothes. In the summer, 68 may feel a bit chilly because it’s hot outside and you’re likely wearing less clothes.
3. It’s 68 according to the thermostat which is only capable of reading the temperature of the air that directly surrounds it, meaning the actual average temperate of the room could be higher or lower.
Let’s say it’s winter and you’re heating to 68. The vent that supplies the heat is on the opposite side of the room as the thermostat. The heat will kick on until the thermostat reads 68, but the air outside the vent could reach a temperature much higher than that before the air around the thermostat heats up. This means the average temperature of the room would be a little higher than 68.
The opposite would happen in the summer, where the air around the vent would become much colder before the air around the thermostat hit 68, meaning the room would be colder on average.
In other words, your thermostat says it’s 68 in both cases, but it’s likely a bit hotter when heating and bit colder when cooling.
Hot air rises, and most thermostats have a thermometer inside them to detect ambient room temperature.
Hot air accumulates in the upper portions of each room until it warms up the lower part of the room.
Air conditioners cool the air, but more importantly they remove humidity from the air. The air coming out of the AC is dryer, so it feels cooler on your body due to your own moisture very lightly evaporating into the dry air.
Doors and windows are generally closed when the heat is on, trapping humid air inside.
There’s something called relative humidity. Air can hold a certain amount of dissolved water. The capacity of the air to hold that water changes with the temperature of the air, with hotter air holding more water than colder air.
If you’re heating up air from the outside, it doesn’t add any humidity to it. While it contains the same amount of water, the relative amount is lower. Because the relative amount is lower, the air actually tries to evaporate moisture out of your skin, since it can hold it better than your skin can. This makes a heated room feel dry.
If you’re cooling down air from the outside, it might actually be holding into more moisture than it can at room temperature. As you cool it down, it actually loses ability to hold water, so it condenses down. This means the air coming out is actually very moist.
Your body senses change in temperature, not the actual temperature. So if you are sitting in a 68F/20C house and touch floors/windows/doors or go out in winter, your body identifies the house as warmer than the rest of the environment. If it’s the summer; the house is cooler than the rest of the environment. But we don’t have a sensor that measures the absolute temperature.
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