After 15 minutes, I checked to see how much heat was coming off the direct vent pipe. I was able to keep my hand on the vertical portion of the vent for as long as I wanted. It was uncomfortable to keep my hand there, but it wasn't painful. The horizontal run where the thimble penetrated the wall was another matter entirely. I could touch it for a couple seconds at most. Guessing it was 190-200 degrees or so up there.