HVAC terms, plain English

HVAC glossary.

The HVAC terms you'll see on a quote or hear from a tech, defined in plain English for Pearland and South Houston homes. Bookmark it.

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Forty-plus terms grouped by category. Keep it open when you read a quote or compare two contractors. The trade has more jargon than it needs.

Equipment

Air Handler: The indoor unit. It holds the blower motor and the evaporator coil, usually with the filter rack. Paired with the outdoor condenser, it makes a complete split system. In Texas homes it usually sits in the attic, a closet or the garage.
Condenser: The outdoor unit. Inside are the compressor and condenser coil, with the fan on top. It dumps the heat pulled out of your house 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 moves it through the system. It is the most expensive part to replace, $1,800 to $3,500 on the systems we work on.
Capacitor: A small metal can in the outdoor unit that stores a charge to start the compressor and keep the fan running. We replace more of these than any other AC part. $180 to $320.
Contactor: The relay that switches the outdoor unit on and off. When the contacts pit, the unit hums or chatters and may not start. It often wears out alongside the capacitor. $190 to $280 to replace.
Evaporator Coil: The indoor coil that pulls heat and moisture out of the air moving across it. Sits inside the air handler. A coil that has gone a couple of years without cleaning loses efficiency.
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. Hairline cracks take a borescope to find, which is why it gets inspected every year.
Heat Pump: A reversible system that cools in summer and heats in winter with the same refrigerant cycle. In a Houston winter it heats for a lot less money than electric strip heat. Inverter models keep heating well through our cold snaps.
Mini-Split: A ductless heat pump system with a wall-mounted indoor head and a small outdoor unit. Single-zone or multi-zone. A good fit for an addition or garage, or a house that can't take ductwork.
Variable-Speed / Inverter: A compressor and blower that ramp from roughly 25 to 100 percent capacity as the house needs it. Compared with single-stage equipment it runs quieter and uses less power. It also pulls more humidity out, which matters here.

Refrigerants

R-22 (Freon): An older refrigerant phased out by the EPA on January 1, 2020. Only reclaimed R-22 is left, and it is expensive. A major repair on an R-22 system is a good time to talk about replacement.
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. Checking it is part of our tune-up.
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 2,000 sq ft Pearland home usually lands between 36,000 and 48,000 BTU/hr (3 to 4 tons), depending on the Manual J.
SEER2: Seasonal Energy Efficiency Ratio version 2. The federal efficiency rating for residential AC since 2023. It replaced the older SEER metric and uses 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 heating and cooling load calculations. It adds up every window and wall in the house, plus the ducts and local design conditions, and outputs sensible and latent load in BTU/hr. This is how equipment is supposed to be sized.
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 a frequent reason one room runs hot while the rest of the house is fine.
Manual S: The ACCA standard for matching equipment to the Manual J load. Checks that the chosen condenser and coil can deliver the calculated capacity at local design conditions. A lab rating alone doesn't tell you that.
Sensible Load: The part of the cooling load that lowers air temperature. It is the larger share of the load in Houston, and equipment has to be sized to it.
Latent Load: The part of the cooling load that removes humidity. In Houston it is a big part. An oversized AC meets the sensible load fast and shuts off before it has run long enough to dry the air, so the house stays damp.
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. When we suspect a duct or filter problem, this is the first number we read.

Indoor air quality

MERV Rating: Minimum Efficiency Reporting Value. The standard rating for air filter particle capture. MERV 8 is basic and MERV 11 is good. MERV 13 is where we steer most homes. MERV 16 is close to HEPA and usually needs 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. Houston coils stay wet most of the year, and that is where the mold grows.
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. Helps with the stuffy air 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. In Houston it earns a place when the AC alone can't keep up with latent load. Oversized systems and vacation rentals are typical cases, and so are spring and fall when the AC barely runs.

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 national model electrical code (NFPA 70), adopted by Texas and enforced by local jurisdictions. HVAC installs follow it for breaker and wire sizing and for the disconnect.
IECC: International Energy Conservation Code. Sets minimum efficiency and insulation requirements. Texas adopts current IECC for new residential construction. It sets insulation depth and window specs, along with minimum HVAC equipment efficiency.
ACCA: Air Conditioning Contractors of America. The residential HVAC trade association. It publishes Manuals J, D and S along with the Quality Maintenance Standard.
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. It has to be abated before anyone disturbs it.

Installation

Aeroseal: A duct sealing process that blows an aerosol sealant through the ducts and closes leaks from the inside, usually in a day. Leaky attic ducts are the main target.
Line Set: The pair of insulated copper refrigerant lines connecting the outdoor condenser to the indoor coil. Brazed at both ends. In Pearland we find a lot of slow leaks at the brazed joint where the line set meets the condenser.
Plenum: The sheet-metal box at the air handler outlet that distributes air into the supply trunks. Leaky plenum seams blow cooled air straight 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 clogged drain turns into a ceiling repair.
V-Zone: FEMA designation for highest-risk velocity flood zones. Requires HVAC equipment elevated above base flood elevation. You see it on Galveston West End beach houses and in Bayou Vista and Tiki Island. Condensers go on the roof or a platform, and mechanical rooms get raised.

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 list grows from what homeowners actually run into.