Glossary

HVAC Glossary

Plain-language definitions for SEER2, AFUE, MERV, refrigerant types, and the other HVAC terms Birmingham Metro homeowners run into when comparing options.

Cooling & Air Conditioning

Condenser / Evaporator Coil The condenser coil (outdoor unit) releases heat collected from inside; the evaporator coil (indoor unit) absorbs it. A dirty or frozen coil on either end is one of the most common causes of poor cooling. Read the full definition → R-410A / R-454B (A2L Refrigerant) R-410A is the refrigerant used in most AC and heat pump systems installed before 2025; R-454B is the newer, lower-global-warming-potential A2L refrigerant now phasing in under federal regulations. Read the full definition → Refrigerant Charge The precise amount of refrigerant a system needs to operate at its rated capacity. Too little (a leak) or too much both reduce efficiency and can damage the compressor over time. Read the full definition → SEER2 The efficiency rating for central AC and heat pumps under the stricter testing standard that replaced SEER in 2023 — it accounts for real-world ductwork resistance, so SEER2 numbers run slightly lower than old SEER ratings for the same equipment. Read the full definition →

Heating & Heat Pumps

AFUE Annual Fuel Utilization Efficiency — the percentage of fuel a furnace converts to usable heat. A 95% AFUE furnace turns 95 cents of every fuel dollar into heat; the rest is lost as exhaust. Read the full definition → Furnace A combustion (gas or oil) or electric-resistance heating unit that generates heat directly, as opposed to a heat pump, which moves existing heat. Read the full definition → HSPF2 Heating Seasonal Performance Factor 2 — the heating-mode efficiency rating for heat pumps, measured the same stricter way SEER2 measures cooling efficiency. Read the full definition →

Indoor Air Quality

MERV Rating Minimum Efficiency Reporting Value, 1-20 — how finely an air filter traps particles. Higher isn't automatically better: too high a MERV rating can restrict airflow on a system not designed for it. Read the full definition →

Ductwork

Static Pressure The resistance air encounters moving through ductwork. Pressure that's too high for the system's design usually points to undersized or restricted ducts and forces the blower to work harder than it should. Read the full definition →

Carrier Equipment

Carrier Factory Authorized Dealer A Carrier dealer designation requiring technician certification, customer-service standards, and installation-quality audits beyond simply carrying the brand. Read the full definition →

By Space & Application

Ductless Mini-Split A zoned heating/cooling system with an outdoor condenser connected to one or more indoor air-handling units, requiring no ductwork — common for additions, garages, and rooms existing ducts can't reach. Read the full definition →

How HVAC Works

AHRI Matched System An indoor and outdoor unit pairing certified by the Air-Conditioning, Heating & Refrigeration Institute to perform at its rated efficiency together — mismatched components can void warranties and underperform. Read the full definition → Air Handler The indoor component that circulates conditioned air through your ductwork — houses the evaporator coil and blower fan, and pairs with an outdoor condenser in split systems. Read the full definition → BTU British Thermal Unit — the base unit of heating/cooling capacity. One BTU is the energy needed to raise one pound of water by one degree Fahrenheit; HVAC systems are typically sized in tens of thousands of BTUs per hour. Read the full definition → Heat Pump A system that moves heat rather than generating it — pulling warmth from outdoor air to heat your home in winter, and reversing to pull heat out and cool your home in summer. Read the full definition → Load Calculation (Manual J) The industry-standard method (ACCA Manual J) for calculating a home's actual heating/cooling demand from square footage, insulation, windows, and orientation — the basis for correct equipment sizing. Read the full definition → Thermostat (Smart/Programmable) A programmable thermostat runs a fixed daily/weekly schedule; a smart thermostat adds remote control, usage learning, and often integration with the rest of your HVAC system's diagnostics. Read the full definition → Tonnage "Tons" of cooling capacity, where 1 ton equals 12,000 BTU/hour. Residential AC systems typically range from 1.5 to 5 tons depending on home size and insulation. Read the full definition →

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