HVAC jargon, translated
25 terms you'll hear from techs, quotes, and spec sheets — each defined in plain English with the Arizona context that makes it matter. Every term links to the questions and guides where it shows up.
The switch-over months: time for the fall system check.
Before the first cold desert night, the heating side needs its once-a-year look — heat exchanger inspection, heat strips, and thermostat changeover included.
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Efficiency Ratings & Sizing
SEER / SEER2
SEER2 (Seasonal Energy Efficiency Ratio 2) measures how much cooling an air conditioner or heat pump delivers per unit of electricity across a season — higher is more efficient.
Full definition ›EER / EER2
EER (Energy Efficiency Ratio) measures cooling efficiency at one fixed, hot condition — 95°F outdoors — rather than averaged across a mild season the way SEER is.
Full definition ›HSPF / HSPF2
HSPF (Heating Seasonal Performance Factor) is the heating-mode equivalent of SEER — it measures how efficiently a heat pump converts electricity into heat across a winter season.
Full definition ›Load Calculation (Manual J)
Manual J is the industry-standard engineering method for calculating exactly how much heating and cooling a specific home needs, room by room — factoring square footage, insulation, window area and orientation, ceiling height, and air leakage.
Full definition ›Ton & BTU
A BTU (British Thermal Unit) is a unit of heat energy; cooling capacity is rated in BTUs per hour.
Full definition ›Systems & Equipment
Heat Pump
A heat pump is an air conditioner that runs in both directions: in summer it moves heat out of your home like any AC, and in winter it reverses to extract heat from outdoor air and move it inside.
Full definition ›Mini-Split (Ductless)
A mini-split is a compact heat pump that conditions a space directly through one or more wall-mounted indoor heads, with no ductwork — just a small refrigerant line-set to an outdoor unit.
Full definition ›Variable-Speed (Inverter)
A variable-speed or inverter system adjusts its compressor and blower output continuously — running at 30% capacity on a mild day and 100% in a heat wave — instead of the on/off slamming of single-stage equipment.
Full definition ›Air Handler
The air handler is the indoor half of a split system: a cabinet containing the blower, the evaporator coil, and the filter rack that circulates conditioned air through your ducts.
Full definition ›Heat Exchanger
In a gas furnace, the heat exchanger is the sealed metal chamber where combustion happens: burner flames heat the metal from inside while household air passes over the outside, keeping exhaust gases and breathing air completely separated.
Full definition ›Parts & Components
Compressor
The compressor is the heart of an air conditioner or heat pump — the pump in the outdoor unit that pressurizes refrigerant and drives it through the system so heat can be absorbed indoors and rejected outdoors.
Full definition ›Capacitor
A capacitor is a small electrical component that stores and releases the jolt of energy the compressor and fan motors need to start and keep running.
Full definition ›Hard-Start Kit
A hard-start kit is an add-on capacitor-and-relay package that gives a compressor extra starting torque, letting it snap on quickly instead of straining against system pressure.
Full definition ›Condenser
The condenser is the outdoor unit of an AC or heat pump: its coil and fan reject the heat collected from inside your home into outdoor air, condensing hot refrigerant vapor back into liquid.
Full definition ›Evaporator Coil
The evaporator coil is the indoor coil where refrigerant absorbs heat from your home's air — warm air passes over the cold coil, comes out cool, and the collected heat rides the refrigerant outside.
Full definition ›Refrigerant
Refrigerant is the working fluid that carries heat through an air conditioner — absorbing it at the indoor coil, releasing it at the outdoor coil, over and over.
Full definition ›R-410A & R-32
R-410A is the refrigerant that has filled most residential ACs since the mid-2000s; R-32 (and R-454B) are the lower-global-warming-potential refrigerants replacing it in new equipment as of 2025 under the federal A2L transition.
Full definition ›Condensate Line
The condensate line is the drain that carries away the water your AC pulls out of the air at the evaporator coil.
Full definition ›Thermostat C-Wire
The C-wire (“common” wire) is the thermostat wire that supplies continuous 24-volt power, letting smart thermostats run their screens and Wi-Fi without stealing power through the furnace control circuit.
Full definition ›Airflow, Ducts & Air Quality
MERV Rating
MERV (Minimum Efficiency Reporting Value) rates how well an air filter captures particles, on a scale from 1 to 16 for residential use — higher numbers catch finer particles.
Full definition ›Static Pressure
Static pressure is the resistance your blower pushes against to move air through ducts, filter, and coils — the blood pressure of an HVAC system.
Full definition ›IAQ (Indoor Air Quality)
IAQ (indoor air quality) describes how clean and healthy the air inside a building is — particulates, allergens, VOCs, humidity, and ventilation all factor in.
Full definition ›ERV / HRV
ERVs and HRVs (energy/heat recovery ventilators) bring fresh outdoor air into a tightly sealed home while transferring heat — and, in an ERV, moisture — between the outgoing and incoming airstreams, so ventilation doesn't throw away the energy you paid to condition.
Full definition ›Arizona Climate
Haboob (Dust Storm)
A haboob is a massive wall of dust driven by thunderstorm outflow winds — central Arizona's signature monsoon event, capable of dropping visibility to near zero in minutes.
Full definition ›Monsoon Humidity
During the North American Monsoon (roughly mid-June through September), moist tropical air surges into Arizona, spiking humidity in a region that's bone-dry the rest of the year.
Full definition ›A to Z
The whole glossary in one alphabetical sweep.
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