A chimney, more than any other part of the building, undergoes more changes in temperature, and therefore more changes in expansion and contraction. Such changes should be the same for all parts of the building that bear the building's weight. Otherwise, sags and worse occur. The photo was taken on a warm day. Note that the rocker is slightly tipped toward the end rather than toward the middle, which means the steel beam is slightly lengthened.
Gas is sold by volume.
Warm gas is expanded gas and occupies more space, and if it passes through your meter, it will be registered as more gas than if it were cooled and more compact. The gas company gains if gas is warm when it goes through your meter because the same amount of warmer gas has a greater volume. Every part of a metal ring expands when it is heated-not only the thickness, but the outer and inner circumference as well. Hence the ball that normally passes through the hole when the temperatures are equal will more easily pass through the expanded hole when the ring is heated. Blacksmiths mounted metal rims in wooden wagon wheels by first heating the rims.