HVAC technician explaining a system component to a homeowner

Plain-English Glossary

HVAC101.
45 terms decoded.

Every HVAC term a homeowner might hear during a service call, install quote, or annual tune-up. Written in plain English by JC Energy Solutions techs. No upsell, no jargon for jargon's sake.

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Efficiency (5) Equipment (13) Refrigerant (5) Diagnostics (9) Airflow (6) Process (3) Credentials (4)

Efficiency

Efficiency terms.

SEER2: Seasonal Energy Efficiency Ratio (2023 standard). Measures AC cooling efficiency over a typical season. Higher is better. Current federal minimum in California is 15 SEER2. High-efficiency systems run 17-22 SEER2.
HSPF2: Heating Seasonal Performance Factor (2023 standard). Heat pump heating efficiency. Higher is better. Federal minimum 7.5 HSPF2. Premium heat pumps reach 9.5-10.5 HSPF2.
AFUE: Annual Fuel Utilization Efficiency. Furnace efficiency rating, expressed as percentage of fuel converted to heat. 80 percent AFUE is standard; 95+ percent AFUE is high-efficiency condensing.
BTU: British Thermal Unit. Standard heat measurement. 12,000 BTUs per hour = 1 ton of cooling. Homes are sized by total BTU load (a 3-ton AC = 36,000 BTU/hr).
Ton: HVAC capacity unit. 1 ton = 12,000 BTUs per hour. Common HD residential systems: 2.5 to 5 ton. Sizing must match Manual J load calc, not guesswork.

Equipment

Equipment terms.

Heat Pump: A single piece of outdoor equipment that both cools (like an AC) and heats (by reversing refrigerant flow). One system for the whole year. Strong fit for HD homes with mild winters.
Mini Split: Ductless HVAC system with one outdoor unit and one or more wall-mounted indoor heads. No ductwork needed. Best for ADUs, garage conversions, room additions, or spaces where central ductwork is impractical.
Compressor: The heart of any AC or heat pump. Lives in the outdoor unit. Pumps refrigerant through the system. Most expensive single part to replace ($1,500-$3,500). Lifespan: 12-18 years with maintenance.
Condenser: The outdoor portion of a central AC or heat pump. Contains the compressor and outdoor coil. Sits next to your house. Also called "the outdoor unit."
Evaporator Coil: The indoor coil. Sits inside the air handler or above the furnace. Absorbs heat from indoor air. Coil failures = refrigerant leaks. Usually replaced in $1,200-$2,400 range.
Air Handler: Indoor blower unit that moves conditioned air through the ductwork. Contains the blower motor, evaporator coil, and air filter. Pairs with a heat pump (no furnace) or sits separately from a furnace.
Furnace: Heating equipment that burns natural gas or propane to warm air. Pairs with a separate AC for the cooling side. AFUE rating measures efficiency.
Heat Exchanger: Metal chamber inside a furnace where combustion gases heat the air without mixing into it. Cracked heat exchangers leak carbon monoxide. Annual inspection is non-negotiable on gas systems.
Capacitor: Small cylindrical electrical component in the outdoor unit. Stores energy to help the compressor and fan motors start. Most common AC failure. Replacement is $185-$325. Lifespan 5-10 years in HD heat.
Contactor: Electrical switch in the outdoor unit that turns the compressor and fan on/off when the thermostat calls. Wears out from arcing over time. Replacement is $185-$285.
Inverter Compressor: Variable-speed compressor that modulates output continuously instead of cycling on/off. Quieter, more efficient, better humidity control. Found on premium tier systems and most mini splits.
Thermostat: Wall-mounted control that tells the HVAC system when to run. Smart thermostats (Nest, Ecobee) add learning, remote control, scheduling. Most modern systems need a C-wire for power.
C-Wire: The "common" wire that delivers steady 24V power to a thermostat. Required for smart thermostats. Older homes often lack one - JCE can run a new wire or install a power adapter.

Refrigerant

Refrigerant terms.

R-410A: The standard residential AC refrigerant from ~2010 to 2025. Being phased out due to high global warming potential. Existing R-410A systems will keep running, but new installs use R-454B starting 2026.
R-454B: Current low-GWP refrigerant for new installs (2026+). Classified A2L (mildly flammable, manageable with proper handling). Replaces R-410A in new equipment. Industry standard for the foreseeable future.
R-22: Legacy refrigerant ("Freon") phased out 2020. Still in many older systems. Recharge cost is $80-$180/lb due to scarcity. Most R-22 leak repairs lean toward system replacement now.
A2L: ASHRAE refrigerant classification: mildly flammable but lower toxicity. R-454B and R-32 are A2L refrigerants. Safe to install with proper procedures and detection equipment.
Refrigerant Leak: AC systems are closed-loop. Refrigerant should never need topping off. If the system is low, there is a leak. Leak repair + recharge is $650-$1,400. Refilling without leak repair is throwing money away.

Diagnostics

Diagnostics terms.

Superheat: Degrees above the refrigerant's boiling point measured at the suction line. Tells the tech if the system is properly charged. Target 8-15 degrees F for most systems. High superheat = undercharged; low superheat = overcharged.
Subcooling: Degrees below condensing temperature at the liquid line. Confirms refrigerant is fully condensed leaving the outdoor unit. Target 8-12 degrees F. Charged properly means superheat AND subcooling within spec.
TXV: Thermostatic Expansion Valve. Meters refrigerant flow into the evaporator coil based on superheat. Replaces older fixed-orifice metering. Found on most systems built after ~2010. $385-$685 to replace.
Static Pressure: Air resistance in the ductwork, measured in inches of water column (in. WC). High static = restricted airflow = strained system. Target under 0.5 in. WC. Measured on every JCE tune-up.
Delta-T: Temperature difference between return-air and supply-air at the indoor unit. Healthy AC: 16-22 degrees F. Below 14 = airflow or refrigerant problem. Above 24 = airflow restriction.
CO: Carbon monoxide. Odorless, colorless, deadly. Produced by incomplete combustion in furnaces. CO detectors required on every floor of gas-heated homes. Furnace inspection includes CO measurement.
Combustion Analysis: Measurement of furnace exhaust gases (CO, O2, stack temperature). Confirms safe and efficient combustion. Part of every JCE fall furnace tune-up. Without it, a "tune-up" is just a filter change.
HSI: Hot Surface Igniter. Ceramic element that glows orange to ignite the burner in modern furnaces. Replaces older standing pilot lights. Lifespan 5-10 years. Replacement: $185-$320.
Thermocouple: Small temperature probe in standing-pilot furnaces. Generates millivolts when hot, telling the gas valve to stay open. Dirty/worn thermocouple = pilot won't stay lit. $145-$245 replacement.

Airflow

Airflow terms.

CFM: Cubic Feet per Minute. Airflow measurement. Target around 400 CFM per ton of cooling. Below that = restricted airflow + premature coil freezing.
MERV: Minimum Efficiency Reporting Value. Air filter rating from 1-16. Higher catches smaller particles but adds airflow resistance. Sweet spot for HD homes: MERV 8-11. Above MERV 13 stresses the blower.
HEPA: High-Efficiency Particulate Air. Captures 99.97 percent of particles 0.3 microns and larger. Cannot be installed in standard return slots - requires bypass setup. $1,200-$2,500 install.
Plenum: Sheet metal box at the top of the air handler that distributes air to the supply ducts. Common location for duct sealing improvements.
Zoning: Splitting one HVAC system across multiple zones (rooms or floors) with separate thermostats and motorized dampers. Useful for two-story homes or homes with hot/cold spots.
Short Cycling: AC runs less than 10 minutes per cycle, repeats every few minutes. Damages compressor. Most common HD cause: oversized AC. Other causes: dirty filter, thermostat location, refrigerant issue.

Process

Process terms.

Manual J: ACCA-developed load calculation that determines correct HVAC size based on square footage, insulation, windows, climate, and orientation. Skip this and you get an oversized AC that short-cycles for 15 years.
Manual D: ACCA-developed duct design standard. Calculates duct size for proper airflow at acceptable static pressure. Most HD homes built before 2010 have undersized ducts.
Manual S: ACCA-developed equipment selection process. Matches the Manual J load to specific manufacturer equipment with their actual performance specs (not just nameplate tonnage).

Credentials

Credentials terms.

EPA 608: Federal certification required to handle refrigerant. Every JCE technician is EPA 608 certified. Anyone touching refrigerant lines without it is operating illegally.
ACCA: Air Conditioning Contractors of America. Industry trade association. ACCA publishes the Manual J, D, S standards. JCE is ACCA-certified.
CSLB C-20: California Contractors State License Board classification for HVAC contractors. JCE license #998538. Verifiable at cslb.ca.gov - never hire an unlicensed installer.
NATE: North American Technician Excellence. Voluntary technician certification covering installation, service, and senior-level expertise. Looked for in hiring and on premium projects.

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