HVAC Glossary: Read Your Quote Like a Pro
SEER2, tonnage, Manual J, short cycling, R-454B — every term on an AC quote, defined in plain English, two sentences each.
- Ton (tonnage)
- AC capacity, nothing to do with weight: one ton moves 12,000 BTU of heat per hour (the melting power of a ton of ice per day, historically). US homes typically need 2–5 tons; sizing is decided by a Manual J calculation, not square footage alone.
- BTU
- British Thermal Unit — the heat-energy unit AC capacity is quoted in. Rule of thumb: 20–25 BTU per square foot of living space, adjusted for climate, sun and insulation. 12,000 BTU = 1 ton.
- SEER2
- Seasonal cooling efficiency under the test standard in force since 2023 — higher means cheaper summers. Federal minimums: 13.4 (North), 14.3 (South). Stepping from 14.3 to 17 SEER2 cuts cooling energy roughly 16%, which pays back fastest in long cooling seasons.
- EER2
- Efficiency at a single hot-day condition (95°F) rather than a seasonal average. Matters most in desert climates where "average" days barely exist — Phoenix buyers should read EER2 alongside SEER2.
- HSPF2
- The heating-season efficiency rating for heat pumps, the winter sibling of SEER2. Federal minimum 7.5; cold-climate models run 8.5+.
- Manual J
- The industry-standard load calculation: room-by-room math on windows, insulation, orientation, leakage and local design temperatures to determine the size system your home actually needs. Any quote without one is a guess — homes change (insulation, windows), so "same size as the old unit" is often wrong.
- Central AC
- One outdoor condenser plus an indoor coil on your furnace or air handler, cooling the whole house through ductwork. The default in most of the US housing stock.
- Ductless mini-split
- An outdoor unit serving one or more wall-mounted indoor heads, no ducts required. The answer for additions, garages, older homes without ductwork and room-by-room control — $3,500–$6,000 per zone installed.
- Heat pump
- An AC that runs in both directions: it cools identically to a standard AC in summer, then reverses to heat in winter at 2–4x the efficiency of electric resistance heat. State and utility incentives vary by address.
- Dual fuel
- Heat pump paired with a gas furnace: the pump carries most of the heating season, the furnace takes over in deep cold. The standard cold-climate compromise where gas is cheap.
- Air handler
- The indoor half of a ducted system when there is no furnace: blower plus coil, moving conditioned air through the ducts. Homes with a furnace use it as the blower instead.
- Evaporator coil
- The indoor coil where refrigerant evaporates and absorbs heat from your air. Ices up when airflow dies (dirty filter) or refrigerant runs low — the classic "frozen AC" call-out.
- Condenser
- The outdoor unit: compressor, coil and fan, rejecting the heat collected indoors. Keep two feet of clearance and hose the coil fins gently each spring; it repays the courtesy in efficiency.
- Compressor
- The pump inside the condenser driving refrigerant around the system — the most expensive component to replace, which is why a failed compressor on a 12-year-old unit usually means replacement math.
- Refrigerant (R-454B / R-32)
- The working fluid that moves heat. New systems since 2025 use lower-global-warming R-454B or R-32 instead of R-410A; the transition nudged equipment prices and matters for future repair costs on older systems.
- EPA Section 608
- The federal certification legally required for anyone handling refrigerants. Certification for every technician is a condition of joining the YourAirCon contractor network.
- Short cycling
- The system starting and stopping in rapid bursts instead of running steady cycles — the signature of an oversized unit (or a failing component). Cold-but-clammy rooms, worn compressors, wasted power. The argument for Manual J sizing.
- Variable speed / inverter
- Compressors and blowers that modulate output instead of blasting on/off. Steadier temperatures, better dehumidification, lower bills — the premium-tier feature that most changes how a system feels to live with.
- Zoning
- Dividing one system's output across areas with separate thermostats and duct dampers — or achieving the same with multiple mini-split heads. Fixes the classic hot-upstairs-cold-downstairs two-story problem.
- Mechanical permit
- The local-government permit AC replacement requires almost everywhere, pulled by your contractor. Ensures code compliance (hurricane strapping, electrical, refrigerant line protection) and matters at resale — treat a no-permit bid as a red flag.
- Load calculation
- The general term for the heat-gain/heat-loss math behind sizing (Manual J is the residential standard). If your quote arrived after a walkthrough with a tape measure and questions about windows, you got one; if it arrived by phone, you did not.
- 25C tax credit
- The former federal Energy Efficient Home Improvement Credit. It covered qualifying heat pumps and central AC, but is not available for property placed in service after December 31, 2025. Check current state, local and utility incentives instead.
- MERV rating
- Filter fineness, 1–16 for home equipment. MERV 8–11 balances filtration and airflow for most systems; jumping to 13+ without checking blower capacity can choke airflow and ice the coil.
Terms decoded, next step priced: 2026 installation costs, what size you need (calculator), and whether a heat pump wins your math.
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