Total external static pressure is measured across the air handler, from return to supply, and compared with the rating, often 0.5 inches of water column for residential equipment. Readings near or above 1 inch point to undersized ducts, restrictive filters, dirty coils or closed dampers, which cut airflow and raise fan energy. Static pressure is the blood pressure of an air system, and checking it is a standard test.
Total external static is 1.1 inches on a system rated for 0.5, that MERV 13 pleated filter in a one-inch slot isn't helping.
Drill test ports in the supply and return plenums on every install; the next tech will need them.
Also heard as
- static
- SP
Related terms
CFM
Cubic feet per minute: the standard unit of airflow through equipment, ducts and outlets.
Duct leakage
Air lost from supply ducts or pulled into return ducts through gaps at joints, seams and connections.
MERV
Minimum efficiency reporting value: a 1 to 16 rating of how well an air filter captures particles of different sizes.
Plenum
A box on the supply or return side of an air handler that feeds or collects several ducts, or a ceiling cavity used as a return path.