Heat Loss through the Head

[Amberjoy]

Before reading the article, may I ask what you are aiming to achieve by asking this question? In other words, if it were just a myth, what would the implications be, you think?

 

[BoltSnap]

Before reading the article, may I ask what you are aiming to achieve by asking this question? In other words, if it were just a myth, what would the implications be, you think?

It is a myth propagated in some dive literature including dive training agency's textbooks. Some textbooks I am reading now say that we lose 75% of our body heat through our heads. This is a gross exageration of the amount of heat that we lose through our heads when we dive. It would imply that we are better off wearing a drysuit over our heads somehow and we would be much warmer than we are now when diving. It doesn't add up. As diving educators, we need to be precise and accurate in the information we pass down to our students and fight this type of myths.

 

[BRT]

It is a myth propagated in some dive literature including dive training agency's textbooks. Some textbooks I am reading now say that we lose 75% of our body heat through our heads. This is a gross exageration of the amount of heat that we lose through our heads when we dive. It would imply that we are better off wearing a drysuit over our heads somehow and we would be much warmer than we are now when diving. It doesn't add up. As diving educators, we need to be precise and accurate in the information we pass down to our students and fight this type of myths.

If we are wearing drysuits with lots of insulation, dry gloves with good insulation, and a wet hood with some flushing (inevitable) we may well be loosing 75% of total heat loss through our head. And improvement in insulation in that area will do more for heat loss than efforts in other directions.

 

[BoltSnap]

If you head is the only part of your body that is losing heat, you will be losing 100% of the heat you are losing through your head in that sense for sure However, if you expose your head and another part of your body with the same surface area, they will be losing heat at the same rate or the head will lose heat with slightly higher % but not much higher.

 

[BRT]

If you head is the only part of your body that is losing heat, you will be losing 100% of the heat you are losing through your head in that sense for sure However, if you expose your head and another part of your body with the same surface area, they will be losing heat at the same rate or the head will lose heat with slightly higher % but not much higher.

I think I agree with you. I've always doubted that the head was many times worse than other unprotected areas but we have trouble covering the head up like we do other areas because we use it to hear and see and breathe. I do think that the body will keep the head warm long after it would have shut off circulation to other parts and this exacerbates the problem. I wear hooded sweatshirts in the winter. It is astounding the difference between the top up and down when it gets cold.

 

[knotical]

... if you expose your head and another part of your body with the same surface area, they will be losing heat at the same rate or the head will lose heat with slightly higher % but not much higher.

I haven’t been able to find a good single reference source, but from looking at several, it appears the rate of heat loss from the head is significantly greater per unit of surface area than from most of the rest of your body because there isn’t much fat insulation on (most) heads, and because vasoconstriction is not as effective on the head. Other areas often mentioned as heat loss areas are the armpits and groin.

Percentage? Hard to say, because there are so many variables. From a diver’s perspective with the head immersed in that great heat conductor called water, and with most of the rest of the body covered by some thermal protection, I could see the head easily being the clear majority contributor. The 75% figure you originally cited could well be true, but they should couple that number with the associated conditions, such as 7-mil wetsuit, no hood, or whatever. I totally agree that any training material that just says something like "the diver losses 75% of body heat through the head" without qualification is notably deficient.

The head is a sufficiently effective heat radiator that it’s well worth wearing a hood in most circumstances. Even in warm water, I'm noticeably less tired after a day of diving when I've worn a hood.

 

[BRT]

I'm not sure about the lack of insulation on my head. A certain group of people seem to think I'm well insulated there.

 

[Darkforeboding]

This falls in line with what I was always told, which was 40%. Add to the surface area of the head that someone might have actually measured how much heat is lost when cold air flows through your sinuses or mouth when breathing, as the sinal passages help to preheat the air you inhale. That wouldn't factor in the same for a diver as the heat loss to water isn't the same as heat loss to air (of course).

I also took note of what Steve_C says above, that your hands and feet, for example, can handle lowered temperature but I don't think your brain can handle quite so much temperature change. It's why we still have hair on our heads, for insulation. Well, some of us, anyway.

DFB

I read it and I am even more confused now, here is what it says:

"18. LOSE MOST OF YOUR HEAT FROM YOUR HEAD? This is a popular myth. Head heat loss is not the majority of heat lost. Not even close. The heat you lose from your head is small compared to the rest of your body, and varies with temperature and exercise.
Head heat loss is linear with temperature, meaning the lower the temperature, the higher percentage head heat loss. At 0 degrees Centigrade, up to about 30 to 35% of heat could be lost through your head at rest. When exercising at about a work rate of 50% of aerobic capacity, head heat loss falls to less than half that.