Static pressure is the amount of pressure a fan has to push and pull against to move air through a duct system.

Static pressure is exerted equally on all sides of a duct system. Every gas furnace data plate/tag has a specification for the temperature rise through that furnace. It is shown in a range like 50-80° or 45-75 °. Those two numbers are the lowest recommended temperature rise and the highest allowed temperature rise through the furnace, this is usually a 30° difference.