My TR7 coupe has the footwell vents, & I have disconnected the water supply from the heater, as I found it blew hot air at me, for a few minutes, every time I parked for a few minutes. I'm sure this helps.
Another thing is the dash carpet I had made, which coveres all that plastic, under the windscreen, & stops it getting so hot, & radiating heat into your face.
The best thing, however, is my sunroof "thing". Its a double glass thing, pivoted at the front, which pops up at the back. With them open, it sucks a regular gale in through the footwell vents, & out through them. They work best with the windows shut.
I recently had a 300 miles drive, in moderate to heavy rain, in the 7. I don't take it out in the rain that often, & I found I could not get enough air onto the screen to keep it clear. Then I tried the vents open, & the sunroof open. The screen demisted immediately.
With the windows shut virtually no rain came in, except when I had to come to a complete stop in a town.
Phil.