The troposphere contains 75 percent of atmosphere's mass-on an average day the weight of the molecules in the air is14.7 lb..(sq. in.)- and most of the atmosphere's water vapor.ater vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface. The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south).
Proper is different from typical or average. Average mantel height is about 54 above the hearth extension. Proper depends on the fireplace size, required clearances and the aesthetic desired, which can vary widely. These are both proper mantel heights: This one's about 48 high.
Building the front wall with the R/O [rough opening] of the fireplace is built just like a standard window is built in a wall. There should be a header above the fireplace [R/O] to transfer load from above around the opening. The height that the fireplace [R/O] starts at all depends on how you want to finish it.