HVAC terms, plain English

HVAC glossary.

HVAC terminology homeowners encounter, defined in plain English with Pearland and South Houston context. Bookmark it.

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Forty-plus terms grouped by category. Use these definitions when reading a quote, talking to a tech, or comparing two contractors. The trade has more jargon than it should; this page is the cheat sheet.

Equipment

Air Handler: The indoor unit that contains the blower motor, evaporator coil, and filter rack. Pairs with the outdoor condenser to make a complete split system. Often installed in an attic, closet, or garage in Texas homes.
Condenser: The outdoor unit that contains the compressor, condenser coil, and outdoor fan. Releases heat absorbed from the home into the outside air. Sized in tons (1 ton = 12,000 BTU/hr of cooling).
Compressor: The pump inside the outdoor condenser that pressurizes refrigerant and circulates it through the system. The most expensive component to replace. Lifespan in Houston: 10-15 years for single-stage, 12-20 years for inverter.
Capacitor: A small cylindrical component in the outdoor unit that stores electrical charge to start the compressor and run the fan. The single most common AC failure. $180-$320 to replace including the service call.
Contactor: The relay that switches the outdoor unit on and off. Pitted contacts cause humming, chattering, and unreliable starts. Often paired with capacitor wear; $190-$280 to replace.
Evaporator Coil: The indoor coil that absorbs heat and humidity from the air passing through it. Located inside the air handler. Cleaning the evaporator coil restores 15-20 percent of lost efficiency on systems not serviced in 2+ years.
Heat Exchanger: The metal chamber inside a gas furnace where combustion gases transfer heat to the air stream. A cracked heat exchanger leaks carbon monoxide; annual inspection with a borescope is the only way to find hairline cracks.
Heat Pump: A reversible HVAC system that cools in summer and heats in winter using the same refrigerant cycle. 3-4x more efficient than electric strip heat down to 35°F. Modern inverter heat pumps maintain efficiency to 17°F.
Mini-Split: A ductless heat pump system with a wall-mounted indoor head and a small outdoor unit. Single-zone or multi-zone. Best for additions, garages, and homes that cannot accept ducted equipment.
Variable-Speed / Inverter: A compressor and blower that modulate from roughly 25 to 100 percent capacity rather than running at fixed speed. More efficient, quieter, and dehumidifies better in humid climates than single-stage equipment.

Refrigerants

R-22 (Freon): An older refrigerant phased out by the EPA on January 1, 2020. Reclaimed R-22 in 2026 runs $100 to $175 per pound, three to five times R-410A. Any major repair on an R-22 system is a strong replacement signal.
R-410A (Puron): The standard residential AC refrigerant from 2010 through 2024. HFC-based, no ozone depletion, but a high global warming potential. Being phased down under the AIM Act.
R-454B: The 2025+ replacement for R-410A in residential AC. Lower global warming potential. Mildly flammable (A2L classification). Requires updated leak detection and safety practices but performance is essentially identical.
Subcooling: The temperature drop of refrigerant after it leaves the condenser before reaching the metering device. Manufacturer-spec subcooling is the primary indicator that an AC has the right charge. Verifying it is a real tune-up step.
Superheat: The temperature rise of refrigerant after it leaves the evaporator coil before reaching the compressor. The pair to subcooling for charge verification. Together they confirm the system has the correct refrigerant charge.

Performance & Sizing

BTU (British Thermal Unit): The unit of heat used to size HVAC equipment. 1 ton of cooling = 12,000 BTU/hr. A typical Pearland 2,000 sq ft home runs 36,000 to 48,000 BTU/hr (3 to 4 tons) depending on Manual J inputs.
SEER2: Seasonal Energy Efficiency Ratio version 2. The 2023+ federal efficiency rating for residential AC. Replaced the older SEER metric with stricter test conditions. Higher SEER2 = less electricity per BTU of cooling.
EER2: Energy Efficiency Ratio version 2. Efficiency at peak load (typically 95°F outdoor). EER2 matters more than SEER2 in Houston because we run at peak load most of the season.
AFUE: Annual Fuel Utilization Efficiency. The federal efficiency rating for gas furnaces. 80% AFUE is mid-range; 96% AFUE is high-efficiency condensing. Higher AFUE delivers more heat per cubic foot of gas burned.
HSPF2: Heating Seasonal Performance Factor version 2. The federal efficiency rating for heat pumps in heating mode. Higher HSPF2 = more heat per kWh.
Manual J: The ACCA standard for residential cooling and heating load calculations. Accounts for every window, wall, and duct in the home plus local design conditions to output sensible and latent load in BTU/hr. Industry standard for sizing equipment.
Manual D: The ACCA standard for residential ductwork sizing. Pairs with Manual J to ensure ducts can deliver the calculated airflow at acceptable static pressure. Skipping Manual D is the single most common cause of room-to-room imbalance.
Manual S: The ACCA standard for matching equipment to the Manual J load. Ensures the chosen condenser/coil pair can actually deliver the calculated capacity at the local design conditions, not just the lab-rated value.
Sensible Load: The portion of cooling load that drops air temperature. About 60-70 percent of total load in Houston. Equipment sizing must match sensible load specifically.
Latent Load: The portion of cooling load that removes humidity. 30-40 percent of total load in Houston. Oversized AC systems satisfy sensible quickly and never run long enough to handle latent. That is why oversize causes humidity problems.
Static Pressure: The resistance to airflow inside the duct system. Measured at the air handler. Total external static above 0.8 inches w.c. starves the blower. The single best indicator of duct or filter problems.

Indoor Air Quality

MERV Rating: Minimum Efficiency Reporting Value. The standard rating for air filter particle capture. MERV 8 is basic, MERV 11 is good, MERV 13 is the residential sweet spot, MERV 16 is HEPA-adjacent and usually requires a bypass cabinet.
HEPA: High-Efficiency Particulate Air filter. Captures 99.97 percent of particles down to 0.3 microns. True HEPA cannot run on a standard residential blower without a bypass setup. MERV 13 is the practical equivalent for most homes.
UV-C Lamp: A coil-mounted ultraviolet light that kills mold and bacteria growing on the wet evaporator coil before they aerosolize. Targets the cold-coil mold problem common to Houston systems. $400-$700 installed.
ERV / HRV: Energy Recovery Ventilator / Heat Recovery Ventilator. Brings filtered fresh outdoor air in while transferring temperature and humidity from the exhaust air to the incoming air. Solves stuffy-house syndrome in tightly built homes.
Whole-Home Dehumidifier: A dedicated dehumidifier ducted into the HVAC system that holds indoor humidity at 45-55 percent year-round. Necessary in Houston when AC alone cannot keep up with latent load (oversized systems, vacation rentals, off-season periods).

Codes & Standards

TDLR: Texas Department of Licensing and Regulation. The state agency that issues HVAC contractor licenses. License lookup at tdlr.texas.gov. Every legitimate Texas HVAC company has a TACL number.
TACLA / TACLB: Texas HVAC contractor license types. TACLA is unrestricted (any tonnage). TACLB is limited to residential and small commercial under 25 tons. Both require passing the state exam.
NEC: National Electrical Code. The federal standard for electrical installation, adopted in some form by every Texas jurisdiction. HVAC installs reference NEC for breaker sizing, conductor gauge, and disconnect requirements.
IECC: International Energy Conservation Code. Sets minimum efficiency and insulation requirements. Texas adopts current IECC for new residential construction. Affects insulation depth, window specs, and HVAC equipment minimums.
ACCA: Air Conditioning Contractors of America. The residential HVAC trade association that publishes Manual J, D, S, and the Quality Maintenance Standard. ACCA certifications signal real industry credentials.
NATE: North American Technician Excellence. The voluntary certification program for HVAC technicians. NATE-certified means the tech has passed standardized exams beyond state licensure.
NESHAP: National Emission Standards for Hazardous Air Pollutants. Federal asbestos rules for renovation. Pre-1980 ductwork in some Pearland-area homes contains asbestos; abatement is required before disturbance.

Installation

Aeroseal: A pressurized-aerosol duct sealing process that seals leaks from the inside of the duct system in a single day. Restores 25-30 percent of conditioned air typically lost to leaks in attic ducts.
Line Set: The pair of insulated copper refrigerant lines connecting the outdoor condenser to the indoor coil. Brazed at both ends. The brazed joint where the line set meets the condenser is the most common slow-leak location in Pearland.
Plenum: The sheet-metal box at the air handler outlet that distributes air into the supply trunks. Leaks at plenum seams waste 5-15 percent of cooling capacity directly into the closet or attic.
Float Switch: A safety device in the indoor drain pan that shuts the AC off when water rises above the safe level. Prevents water from overflowing into the air handler closet and through the ceiling. Bypassing it is how a $150 drain cleaning becomes a $4,000 ceiling repair.
V-Zone: FEMA designation for highest-risk velocity flood zones. Requires HVAC equipment elevated above base flood elevation. Common on Galveston West End beach houses, Bayou Vista, Tiki Island. Roof or platform-mounted condensers, elevated mechanical rooms.

Term we missed?

If you ran into HVAC jargon on a quote and we did not cover it here, send it our way through the contact form and we will add it. The glossary grows with what homeowners actually encounter, not what shows up in a sales script.