Learning Center
HVAC Glossary
Every term we use on the site, defined in plain language — and linked to the guide that goes deeper.
- AFUE (Annual Fuel Utilization Efficiency)
- How efficiently a furnace turns fuel into heat over a year, as a percentage. A 95% AFUE furnace delivers 95% of the fuel's energy as heat. Modern furnaces range ~80–98%. Learn more →
- AHJ (Authority Having Jurisdiction)
- The local building/mechanical department that issues HVAC permits and inspects the work. Rules and fees vary by jurisdiction. Learn more →
- Duct leakage
- Conditioned air lost through gaps in the duct system — commonly 20–30% — wasting energy and hurting comfort. Learn more →
- Evaporator coil
- The indoor coil where refrigerant absorbs heat from your home's air; pairs with the outdoor condenser. Learn more →
- Heat exchanger
- The furnace component that transfers burner heat to your air while keeping combustion gases separate. A cracked heat exchanger is a safety hazard. Learn more →
- Heat pump
- An electric system that moves heat instead of burning fuel — it cools in summer and reverses to heat in winter, often with a backup heat source for the coldest days. Learn more →
- HSPF2 (Heating Seasonal Performance Factor 2)
- The heating-efficiency rating for heat pumps under current test standards. Higher is more efficient. Learn more →
- Load calculation (Manual J)
- The industry method for sizing equipment to a specific home using insulation, windows, orientation, and more — the right way to avoid an oversized system. Learn more →
- Mechanical permit
- Local authorization (plus inspection) to install or replace HVAC equipment, confirming the work meets the adopted code. Learn more →
- MERV (Minimum Efficiency Reporting Value)
- A filter's particle-capture rating (1–16 for homes). MERV 8–13 suits most homes; higher needs a system that can handle the airflow resistance. Learn more →
- NATE certification
- North American Technician Excellence — an industry credential verifying a technician has passed rigorous HVAC competency exams. Learn more →
- R-410A
- A refrigerant phased out for new residential equipment as of 2025 under the EPA AIM Act. Still serviceable, but recharge costs have risen, affecting repair-vs-replace decisions. Learn more →
- R-454B (A2L)
- A lower-global-warming refrigerant replacing R-410A in new equipment. Mildly flammable (A2L class), requiring trained handling and leak detection. Learn more →
- SEER2 (Seasonal Energy Efficiency Ratio 2)
- The current efficiency rating for air conditioners and heat pumps, measured under updated 2023 test conditions. Higher SEER2 means lower cooling cost. Learn more →
- Sheet Metal Workers Local 36
- The union whose apprenticeship and standards Degenhardt's technicians are trained under — the basis for our custom-ductwork craftsmanship. Learn more →
- Tonnage
- A measure of an AC/heat pump's cooling capacity (one ton ≈ 12,000 BTU/hr). Correct tonnage comes from a load calculation, not square footage alone. Learn more →