HVAC Basics

Compare supply-side and return-side duct leakage, including operating pressure direction, comfort effects and the measurements needed to locate each path.

Learn how pressure-pan testing screens individual registers for duct connections to outdoors, what a high reading suggests and why it is not a CFM test.

Compare total duct leakage with leakage to outside, including the test boundaries, equipment required and why the two CFM25 values answer different questions.

Understand what CFM25 represents, why floor-area normalization matters and which test conditions must match before two duct leakage results are compared.

See how a Duct Blaster test seals registers, controls duct pressure and measures leakage, including setup details needed for a defensible result.

Learn how residential duct leakage testing measures openings at a stated pressure, what the result cannot locate, and which conditions affect the reading.

Dual-fuel changeover depends on capacity, operating cost, equipment limits and controls. Learn why one universal outdoor temperature does not fit every system.

Total AC capacity includes sensible and latent work. Learn how latent capacity is identified, why nominal tonnage cannot predict it and what affects it.

A furnace room needs an approved combustion-air strategy based on appliances, enclosure, exhaust equipment and venting—not an arbitrary wall opening.

Low subcooling may come from undercharge, insufficient liquid, flash gas, operating conditions or a bad reading. Learn why it does not prove a leak alone.