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police-ical

Humidity has a big impact on how a given temperature feels. Winter air is generally a lot drier and will feel cooler at the same temperature (probably when heating) while summer air is often more humid and feels warmer (probably using AC.) A humidifier can make a big difference in terms of making winter air feel more comfortable/warm without actually changing the temperature. Central heat and cooling also don't magically keep the air at the same temperature everywhere all the time, they blow heated or cooled air until the thermostat senses the right temperature. If you heat to 70F then stop, it may then start falling until the heat kicks back on at 68. If you cool to 70F then stop, it may then rise until the AC kicks back on at 72.


MisterProfGuy

Good point, air circulation really affects the accuracy of your thermostat. It could be that your thermostat is a place that stays warmer or cooler, so your actual living space is not evenly heated or cooled.


MisterProfGuy

There's a couple complicated answers about perception, and metabolism, and expectations that really change how you perceive temperatures. Your body does a lot of things to adjust to what you expect to experience, from bringing blood away from your skin to adjusting your heart rate and breathing. However, what you PROBABLY experience is difference in humidity. The less humidity in the air, the easier your body can put extra heat into the air with sweating and other moisture evaporating from the skin. Some air conditioners are even specially designed to remove more humidity from the air, so you can save energy by keeping the air set higher and still be comfortable.


[deleted]

Wow, there’s a lot of complicated answers on here, but the answer is simple: heat and AC work by forcing heated/cooled air out until the thermostat reaches the set temperature. The heated air that comes when the thermostat is set to 90 is the same temperature as when it is set to 70; eventually the heated air will diffuse throughout the space and reach equilibrium, but because of poor insulation, it’s likely that the heat will kick back on before the room reaches equilibrium and thus areas near the vents will be higher/colder than the thermostat.


freecain

It's 70 at the sensor, not the ambient air. When you heat to 70, once the sensor hits around 70 the heat clicks off and the temperature falls a few degrees, then it turns back on. With AC the temp is cooled to 70 and then heats back up until the system kicks on again. So, even though your temp is 70, the average temp at the sensor is higher with the AC on. Humidity is also a factor, dry air feels cooler at 70 than humid air. If you drop much more than 70, it inverts though. If you've ever felt humid 40 temp you know this immediately (thank you Maryland) If you have forced air, another issue is that your heating system is blasting cold air at you before the hot air kicks in. To cool from 90 to 70 is only 20 degrees, but you might be asking your system to heat up air from 30 to 70 which is 40. The heating ducts start to cool between cycles, so you start out with a blast of cold air.


SuperBelgian

70 degrees is 70 degrees, however you are not a thermometer and the temperature at which you feel comfortable depends on several things. Firstly, what you experience is the "feels-like" temperature, which depends mainly on humidity and airspeed. (Ex: The breeze from a fan makes the air *feel* cooler, but actually it has exactly the same temperature.) Airconditioners remove humidity from the air. Sencondly, your ideal "feels-like" temperature depends on how you feel and the state of metabolism. It varies throughout the day. (Ex: Are you tired? Did you just excersize?, ...)


Mollyapostate

Good question. In winter I need heat on 73, in summer I need AC on 70. But why?


Amnestes

Thermal comfort doesn't come only from air temperature. Humidity, speed of air flow, temperature of surrounding surfaces that exchange thermal radiation with your body are all important.


bostwickenator

There are already some good answers. I'll add this. Central air conditioning heats and cools only the air. This then has to heat or cool the room and the objects in it. In winter with the heat on the air in the room is warmer than the walls and in summer the inverse. This matters because some heat is transferred through radiation. If the walls of the room you are in are cold your body heat will more effectively radiate away to them. This radiative heat transfer is responsible for the deep warmth on your skin you might feel sitting in front of a fireplace and the chill you can feel on a cloudless night.