Heat is not an issue for me, even here in Florida.

Back when the speed limit was 55 on the interstates, I preferred to do my traveling in a full face helmet. It was just more comfortable not getting hit in the face with stuff. A 3/4 helmet with face shield was okay, but they always caught the wind wrong, so they just weren't comfortable after a few hours on the road. The rest of the time, I wore a half shell.

Today, if I want to get on the interstate, I have to wear a half shell with goggles over my glasses. The higher speed limits mean more shaking of the helmet and a full face helmet that shakes also shakes my glasses, triggering a migraine which makes it impossible for me to see to ride at all. The full face helmets are okay up to about 60 mph in calm air, but a headwind or side gusts will force me to ride slower when I wear one. The half shell and goggles work fine up to 90 mph.

I wear the flip up full face helmet, most of the time for local riding on the back roads. It's just more convenient than putting in earplugs to reduce the wind noise from the half shell anytime I am going to be moving at 35 mph or faster. The flip up is okay without the earplugs as long as I don't go any faster than about 50 mph.

regards,
Joe  

Oh yeah. I have a full face, but do go with half on those hot muggie days in TN. I'm all about safety first. Like the full face helmet best myself.  

Up here in Western New York, heat is usually not a problem, but in the summer we will get a stretch of 90's. When I rode sport bikes, I always wore a full-face, now that I am on a custom, I wear a half. Just more comfortable to me. And if it weren't for our Helmet law, I would sometimes ride without a helmet. I guess it is a personal decision, risk vs. reward, what are you riding for? Pleasure or commute?  

I live in Tucson, AZ., I wear a full faced helmet year round.  During our long hot summers I ride with my face shield open.  

On the highway, I use my fullface.
If I am just street putting, it is the half shell.
IMO, the full face is a lot safer & protective.