HVAC Basics

Learn how outdoor moisture, infiltration, ventilation, occupants and indoor design conditions create latent load inside a Manual J cooling calculation.

Heating design temperature is a standardized local weather condition used to calculate peak load—not the coldest temperature ever recorded.

Compare cold-climate and standard heat pumps using certified low-temperature capacity, COP, controls, sizing and backup needs—not marketing labels.

Restrictions and undercharge can both starve an evaporator. Learn how temperature drops, superheat, subcooling and liquid-line evidence separate them.

A low-ambient cutout intentionally blocks heat-pump compressor operation below defined conditions. The correct setting depends on equipment, load and backup heat.

Relative humidity changes with temperature; dew point tracks moisture content differently. Learn which reading helps explain comfort, condensation and AC load.

A tripped furnace rollout switch is a combustion-safety stop. Learn why not to reset it, what warning signs matter, and what must be inspected.

Frequent auxiliary heat can reflect defrost, recovery, cold-weather capacity or a control problem. Learn what to observe before changing thermostat settings.

Size a whole-house dehumidifier from moisture load, rating conditions, climate, ventilation, infiltration and volume—not square footage alone.

Time-temperature defrost uses runtime and coil temperature; demand defrost adds evidence intended to identify actual frost need.