Hi. Consider a plenum with a small restricting outlet. Highly heated gas constantly flows through the plenum, and a build-up, or congestion of high-pressure gas exists in the plenum due to the restricting outlet pipe. The intake flow of gas does not change. 1. A hotter plenum should increase the gas pressure since there is a small amount of confinement due to the restricted outlet. 2. But, the hotter gas expands more, decreasing pressure/density. Which of these is true?