It's still 72. Why am I cold?

December 11, 2008 12:07 AM

Why does my apartment feel colder in the winter than in the summer, when the thermostat reads the same?

My apartment is roughly 72 degrees (fahrenheit) year round. In the summer, I'm perfectly comfortable sitting around in shorts, a t-shirt, and sandals. But in the winter - although the temperature reads the same inside - I need pants, warm socks and possibly a long shirt to feel comfortable (even if I don't leave the house at all during the day). What's going on here? Is there a scientific explanation?

posted by chundo to science & nature (21 comments total)

A thermostat usually has a sensor that reads the temperature at a particular location within the apartment. I would theorize that during the summer your apartment is evenly 72 degrees throughout, but during the winter the temperature distribution is uneven, with only the region immediately around the thermostat's sensor being 72 degrees and the rest of the apartment being lower than that on average.

You could test this experimentally by getting a bunch of thermometers and placing them throughout the apartment. Be sure to place one next to the thermostat as a baseline.

(Of course, it's also possible that your thermostat is broken and is telling you that it's 72 degrees no matter what.)
posted by XMLicious at 12:13 AM on December 11, 2008 [1 favorite]

Because of a greater temperature gradient in the winter between the exterior walls and the center of the apartment, where the thermostat is?
posted by zippy at 12:14 AM on December 11, 2008

Um, I don't think the answer is connected with heat gradients away from thermostats, unless the space is very large and windows old and inefficient.

It's more to do with relative levels of humidity. In the summer, the air holds more moisture, which reduces the effectiveness of the skin's ability to shed heat through the evaporation of sweat. Therefore, the body temperature rises, and you feel warmer at 72 degrees.

Winter air is less humid. Sweat, even in minute particles, evaporates instantly, and the body cools more quickly at 72 degrees. If you were to raise the humidity of the room with several humidifiers running at full throttle, you'd probably feel warmer.
posted by Gordion Knott at 12:22 AM on December 11, 2008 [3 favorites]

It's also only 72deg in the summer time if you have air conditioning. Without it your thermostat merely guarantees that it's at least 72.
posted by mce at 12:43 AM on December 11, 2008

IMHO, it's all psychological.

I don't think our bodies are very good at judging absolutes: color, illumination, volume, temperature, etc. We base everything on relative measurements, and our baseline is whatever happens to be our immediate environment.

For example, when I ski with orange tinted goggles it's only a couple minutes before the world looks normal. Our brains filter out the tint because they know what snow and trees are supposed to look like.

Crank up the volume on your headphones and try to carry on a normal conversations. You can do it, but at least I have to keep consciously reminding myself to try and whisper a bit.

Same thing with temperature. You know it's supposed to be cold outside in the winter, so 72 feels cold. In the summer you know it's supposed to be warm outside so 72 feels warm. Not to discount humidity and such -- I think it plays a small roll -- but I think perception dominates.
posted by sbutler at 12:54 AM on December 11, 2008

Assuming you have a heater and a cooler operating off the thermostat, in summer, the cooler comes on at 73 and operates until it drops to 72, in winter the heater comes on at 71 and heats until it gets to 72, so on average, the place will be half a degree cooler in winter and half a degree hotter in summer, for a cumulative whole degree different.
In practice, the thermostat might operate over a larger range, not kicking in until the temp is 1.5 or two degrees different, then there is the lag while the heat change takes effect.
Add to this any areas away from the thermostat that are closer to the outside - they will always be cooler than the thermostat in winter, warmer in summer.
posted by bystander at 1:55 AM on December 11, 2008

In summer draughts will probably be 72 or higher, in winter significantly below that.

Personally, my thermostat is at 66 and I layer up for winter.

*mutters something about environment
posted by mandal at 3:46 AM on December 11, 2008 [1 favorite]

Gradients, schmadients. The outside walls are *cold* in the winter, *hot* in the summer. Radiant heat transfer from you to the wall is posive in the winter (i.e. you're warming up the walls - feel cold) and negative in the summer.

At least, that's how it is for my poorly-insulated, all-brick house.
posted by notsnot at 4:03 AM on December 11, 2008 [2 favorites]

There are 4 ways the body loses heat: conduction (direct contact with something cooler), convection (via air currents), radiation (radiant heat loss via infrared radiation), and evaporation (sweat and respiratory water evaporation) Depending on how well insulated and drafty your house is convection and radiation will come into play, but as mentioned above the relative humidity will be much lower in winter (the colder outside air has less evaporated water in it to begin with) so evaporation is the major culprit.
posted by TedW at 4:44 AM on December 11, 2008

Also, the thermostat might not be located so as to take an accurate reading of the entire house; get a thermometer and check the other rooms and you might find that the thermostat is in a warmer or cooler part of the house and so its temperature is not truly representative of what you are experiencing. For example, if it is near the kitchen it will be too warm and thus shut off the heat too soon, leaving the rest of the house colder than the set temperature.
posted by TedW at 4:47 AM on December 11, 2008

notsnot nailed it.
posted by Dorri732 at 5:01 AM on December 11, 2008

There are more things at play too. One is that the humidity is higher in the summer, and wet air of the same temperature feels warmer.

Also, the thermostat reads temp at eye level, or wherever it is placed. Just like in water, houses develop thermoclines where different temperature air settles at different levels. While it might be 70 at eye level in the winter, the floor is probably closer to 63-65, while the air above your head might be 73-74. In the summer, not so much.

This is one of the major arguing points for radiant floor heat---the air at your torso feels warmer in a radiant system and there's not as much mixing versus a forced air system.
posted by TomMelee at 5:24 AM on December 11, 2008

notsnot writes "Gradients, schmadients. The outside walls are *cold* in the winter, *hot* in the summer. Radiant heat transfer from you to the wall is posive in the winter (i.e. you're warming up the walls - feel cold) and negative in the summer."

This is a significant factor. It is the reason why houses with in floor radiant heat can set the thermostat lower. The floor isn't stealling heat from your body. You can see this effect for yourself in a room with good size windows. First acclimatize yourself to the room, preferably at night. Then cover the windows with heavy blankets. You'll feel warmer immediately because your body isn't losing as much radiant heat via the cold glass of the windows.
posted by Mitheral at 5:25 AM on December 11, 2008

Gradients, schmadients. The outside walls are *cold* in the winter, *hot* in the summer. Radiant heat transfer from you to the wall is posive in the winter (i.e. you're warming up the walls - feel cold) and negative in the summer.

yup, well that and the air is probably drier and drier air always feels slightly cooler, but the radiant heat transfer is a far larger factor I believe.
posted by caddis at 7:11 AM on December 11, 2008

In addition to what everyone said above, due to the variances in heating in the winter, you could lower your thermostat and most of your domicile would feel pretty much exactly the same, the bonus is that say you were to lower it to 68 you would save a boatlaod of cash over the course of the winter, and you would also lower your carbon footprint.

Just a thought...
posted by BobbyDigital at 8:28 AM on December 11, 2008

Like the mean radiant temperature of your surfaces, humidity and air speed are other environmental factors besides air temperature that influence human thermal comfort.
posted by glibhamdreck at 9:21 AM on December 11, 2008

My first thought is similar to those of TomMelee and TedW. Our house is a perfect example of how thermostat placement can cause misread temperatures. We don't have central heating. Our downstairs thermostat, in a great room that takes up a large part of the first floor, is currently set to 70 degrees and is reading 71. It's a couple feet to the left and above the gas heater.

There's a thermometer on the kitchen counter about ten feet away from the thermostat--the temperature of this location is much more typical of the room as a whole. It's reading 64. I'm wearing a (admittedly, kind of light) sweater, long-sleeved shirt, long pants, and socks, and am freezing my fucking ass off. Actually, after I finish writing this comment, I'm going to wrap myself in a blanket.

We do have more extreme gradients than most people for a number of reasons, but I think the point is still valid. If you don't have heating and cooling coming from the same location things will be different in the summer; also, of course, cold air sinks and hot air rises.

You could get a thermometer and see how readings vary in different places.
posted by Herkimer at 10:27 AM on December 11, 2008

Wow, I just converted 72F to celsius, you sure keep the place warm in winter!
My thermostat for heating is set at 64F and we don't have cooling (top temps here around 85F). Doesn't all this heating and cooling cost a fortune?
posted by bystander at 1:10 PM on December 11, 2008

mandal & bystander: I don't actually keep it at that temp, that's just what temp it usually is. Lots of southern sun, and I'm surrounded by neighbors who apparently have their heat cranked to 85 (this is a condo building).

There's not much in the way of drafts, and since only about 10% of my walls are exterior, I'm guessing it's the humidity thing. I'll crank up the humidifier and see what happens!
posted by chundo at 3:14 PM on December 11, 2008

I think it is partially related to temperature gradients, but not the way they were described in the first two comments. In particular:

I would theorize that during the summer your apartment is evenly 72 degrees throughout, but during the winter the temperature distribution is uneven, with only the region immediately around the thermostat's sensor being 72 degrees

and

Because of a greater temperature gradient in the winter between the exterior walls and the center of the apartment,

In winter, the temperature gradient is from cold on the outside to hot at the thermostat. In the summer it if from hot outside to cold at the thermostat. Because these two effects are in opposite directions, they accentuate one another. Together they become quite significant! In addition, for the same basic reason, a cold draft in the winter is a hot draft in the summer :)

It is true that heating vents are located in such a way to minimize these effects, but I think they are very hard effects to minimize.

I'm sure humidity also plays a role too..

Lots of southern sun, and I'm surrounded by neighbors who apparently have their heat cranked to 85 (this is a condo building). [...] There's not much in the way of drafts, and since only about 10% of my walls are exterior,

Now that is very interesting.. Certainly worth trying the humidity thing, and it will be interesting to hear the results!
I've always loved the idea of condo/townhouse owners who leach their heat from oppulant neighbours. Yes, you are increasing their heating bills! :)
posted by Chuckles at 2:54 PM on December 13, 2008

I've always loved the idea of condo/townhouse owners who leach their heat from oppulant neighbours. Yes, you are increasing their heating bills!

Oh, it's not by choice. Our heat just never turns on even if we set it to 70. The only way I could contribute back is if I set the heat so high I was sweating all day!
posted by chundo at 3:53 PM on December 13, 2008