Airflow & Static Pressure
TESP, CFM per ton and duct problems.
Belt-Drive Blowers: Belt Tension, Pulley Alignment, Bearings and Setting Airflow
How to service a belt-drive blower on older furnaces, air handlers and rooftop units, including belt tension and alignment, bearings, adjustable pulleys and how they change airflow.
400 CFM per Ton: Where the Rule Comes From and When It's Wrong
Why 400 CFM per ton is the default cooling airflow, when to set airflow lower or higher, and how to check what a system is actually moving.
Total External Static Pressure: How to Measure It and What's Normal
Measure total external static pressure with a manometer, compare it to the equipment's rating, and use it to find airflow restrictions.
Furnace Temperature Rise: How to Measure It and What the Reading Means
How to measure furnace temperature rise correctly, where the normal range comes from, how to estimate airflow from it, and what a high or low rise tells you.
How to Test a Blower Motor: PSC, Constant-Torque ECM and Variable-Speed ECM
How to tell which kind of blower motor you have and test it the right way, from capacitor and amp checks on PSC motors to control signals on constant-torque and variable-speed ECMs.
Frozen Evaporator Coil: Causes, Safe Thawing and What to Check
Why AC evaporator coils freeze, how to thaw one safely, and the order to check airflow, charge and metering once it's thawed.
MERV Ratings and Filter Pressure Drop: Picking a Filter That Won't Choke the System
What MERV ratings mean, how filter pressure drop affects airflow and static pressure, and how to choose a filter without restricting the blower.