Answering the age old question...

Do you lose more heat from your head than other parts of your body?

No. At rest, your head loses the same amount of heat as a comparably exposed portion of your body -- in this case about 7%.

But wait...

Yes. When you start to exercise and before you sweat, your head vents up to 55% of your body heat. At some point, your head gets too hot, so your body sends blood to your skin to cool down your head -- sending your heat loss back down to 7%.

Shivering hypothermia victims don't get the benefit of vasodilation (cooling through the widening of blood vessels, in this case, in the skin) and thus lose 55% of their body heat constantly through their head (put a hat on 'em!). Wet heads also lose more heat, so keep your head out of the water if you're cold.

In the end, 7% is still a lot of heat loss considering that the rest of our body (besides our hands) are covered up when the weather is cold. So if you wear a hat, you'll still feel warmer than without one!

Source: Wilderness Medicine