People are mostly water. Bone is a little denser, fat is a little less dense. Skinny people do tend to sink in a pool and fat people tend to float, but I still claim the differences are small. I am not sure about the other factors, other than my wife has cold hands.

I think there’s more to this seasonal differential than clothing. The body re-adapts to some extent, and I think a lot depends on what we become accustomed to. I encourage clients to take advantage of our ability to adapt to save energy. Over the years, I’ve intentionally extended my comfort range to 77-78 in summer and 69-70 in winter. I will be entering my eighth decade at my next birthday, so I’m wondering if my winter temperature preference will start climbing.

On a related topic… many people prefer lower temps while sleeping, especially in winter when blankets provide warmth. I’m curious how many people I turn down the AC at night. Personally, I have to reduce the master zone to 73 while sleeping, even with the ceiling fan. Unfortunately, I’ve not been successful at persuading my body to adapt to anything higher.

Then I noticed my co-workers in the spring. The weather warmed up and the women wore more dresses and summery type outfits. They dressed for the weather. Lighter clothes for warmer weather. And then they would complain about freezing in the office. Which always seemed odd that as the weather warmed up, the cold complaints increased. But that’s because the outfits changed.

I might suggest that temp settings could also be seasonal.

Roy, early on you said “assuming density is constant.” I’m pretty sure that’s not the case, though. Women have a lower density than men, so mass probably would be a better quantity to use. And then there’s the ASHRAE statement, which says, “Women’s skin temperature and evaporative loss are slightly lower than those for men, and this balances the somewhat lower metabolism of women.” Wouldn’t the lower metabolism also balance out the higher surface-to-volume ratio, if it is higher?

Allison: I just kind of threw that comment out there as an initial thought, but the more I think about it, the more I think it has merit. I have reviewed past literature on thermal modeling of the human body by Fanger, Gagge, and others. People generate heat internally due to metabolism and the amount of that generation primarily depends on activity level and the mass or volume of the body (assuming density is constant). People have to expel all of that internally generated heat to the ambient in order to maintain a constant body temperature. Sensible heat transfer to the ambient depends primarily on the U-value (clothing level and air velocity), the surface area, and the temperature difference. If you write out all of the equations, you will see that the required ambient temperature to maintain this heat balance will depend on the surface-to-volume ratio (dissipated heat to generated heat) among other things. Since a sphere has the lowest surface-to-volume ratio, it would mean that people who are more spherically-shaped prefer cooler ambient temperatures. That seems to be true. Do women generally have higher surface-to-volume ratios? It seems like it, but more study is needed.

Shae, yes, our thermoregulation definitely changes as we get older. I don’t get cold nearly as easily as I used to. And a few years ago, my wife’s stepdad needed his house very warm. If the thermostat was set below 78° F in winter, he’d complain. I learned to dress as lightly as possible when I’d go over there.

I’m not gonna touch that one, Roy. :~)