HVAC Glossary

AFUE (Annual Fuel Utilization Efficiency)

How efficiently a furnace turns fuel into heat over a year, shown as a percentage. A 95% AFUE furnace converts 95% of its fuel to usable heat. Higher AFUE means lower heating bills.

Air Handler

The indoor unit that moves conditioned air through your ducts. It houses the blower and the evaporator coil. In a heat-pump system it works year-round; with a furnace, the furnace blower does this job.

A2L Refrigerant

A safety classification for 'mildly flammable, low-toxicity' refrigerants, including R-454B. A2L refrigerants are handled safely with updated equipment, leak detection, and code requirements by trained technicians. Learn more

BTU (British Thermal Unit)

A unit of heat energy. In HVAC, cooling and heating capacity are measured in BTUs per hour. 12,000 BTU/hr equals one 'ton' of cooling.

Capacitor

An inexpensive electrical component that gives motors (the fan and compressor) the jolt they need to start and run. A failed capacitor is one of the most common — and most affordable — AC repairs. Learn more

Compressor

The heart of the outdoor unit. It pumps refrigerant through the system to move heat out of your home. A failed compressor is one of the most expensive repairs, and often a tipping point toward replacement. Learn more

Condenser (Outdoor Unit)

The outdoor cabinet that releases the heat pulled from your home. It needs clear airflow — keep about two feet of space around it and clear of weeds, leaves, and grass clippings.

Condensate Drain

The line that carries away water your AC removes from the air. When it clogs, a safety switch often shuts the system off on purpose to prevent water damage — a common 'AC stopped working' cause.

Changeout

Industry term for replacing existing HVAC equipment (such as swapping an old AC or furnace for a new one). A changeout typically requires a mechanical permit and inspection. Learn more

Ductless / Mini-Split

A system that heats and cools without ductwork, using one or more wall- or ceiling-mounted indoor units linked to an outdoor unit. Great for additions, garages, and rooms that are always too hot or too cold.

Evaporator Coil

The indoor coil where refrigerant absorbs heat from your home's air. If airflow drops or refrigerant is low, this coil can freeze into a block of ice and stop cooling.

Heat Pump

An all-in-one system that both cools and heats by moving heat (rather than burning fuel). In Central Texas's mild winters, a heat pump is an efficient option for many homes. Learn more

HSPF2 (Heating Seasonal Performance Factor 2)

The heating-efficiency rating for heat pumps, the winter counterpart to SEER2. Higher HSPF2 means more efficient heating.

IAQ (Indoor Air Quality)

How clean and healthy the air inside your home is. IAQ is affected by filtration, ventilation, humidity, and contaminants — and improved with the right filter, duct care, and devices like whole-home air purifiers. Learn more

Load Calculation (Manual J)

The industry-standard method for sizing a system to your specific home — accounting for square footage, windows, insulation, and orientation. Proper sizing prevents an oversized, short-cycling, humidity-prone system. A real quote includes one. Learn more

MERV Rating

A 1–16 scale of how much an air filter captures. Higher MERV traps smaller particles but can restrict airflow if the system isn't designed for it — the right balance matters more than the biggest number.

R-410A

The refrigerant used in most residential systems installed before 2025. It's still legal to service, but it's being phased down, so its price has risen — a factor in repairing older, leaky systems. Learn more

R-454B

The lower-global-warming-potential refrigerant replacing R-410A in new equipment as of 2025. It's an A2L (mildly flammable) refrigerant handled safely by trained, EPA-certified technicians. Learn more

Refrigerant

The fluid that carries heat through your system, absorbing it indoors and releasing it outdoors. Low refrigerant almost always means a leak — it should be found and fixed, not just topped off.

SEER2 (Seasonal Energy Efficiency Ratio 2)

The current cooling-efficiency rating for AC systems and heat pumps. Higher SEER2 means lower running cost. Federal rules set a regional minimum SEER2 for new equipment sold in Texas. Learn more

Short Cycling

When a system turns on and off too frequently, often because it's oversized or has a fault. Short cycling wears out parts, wastes energy, and leaves humidity behind.

Tonnage

The cooling capacity of a system, measured in 'tons' (1 ton = 12,000 BTU/hr). Tonnage should match your home's load — bigger is not better. A load calculation determines the right size. Learn more

Two-Stage / Variable-Speed

Equipment tiers above basic single-stage. Two-stage and variable-speed systems run at lower outputs most of the time for steadier temperatures, better humidity control, and quieter operation.

Zoning

Dividing a home into independently controlled areas (e.g., upstairs vs. downstairs) using dampers and multiple thermostats — a fix for rooms that are always too hot or too cold. Learn more

AHJ (Authority Having Jurisdiction)

The local government body that issues permits and inspects work — usually your city's building department, or the county in unincorporated areas. Every city we serve is its own AHJ with its own rules and fees. Learn more

Auxiliary / Emergency Heat

The backup heat a heat pump switches to (usually electric strips) when it's too cold outside to pull enough heat from the air, or when the system is defrosting. Seeing 'aux heat' on the thermostat during a hard freeze is normal; seeing it constantly is not. Learn more

Blower Motor

The motor that drives the indoor fan, pushing conditioned air through your ducts. Newer ECM (variable-speed) blowers use less electricity and run more quietly than older single-speed PSC motors.

Contactor

An electrical switch in the outdoor unit that lets the thermostat turn the compressor and fan on and off. A pitted or stuck contactor is a common, affordable reason an outdoor unit won't start or won't shut off. Learn more

Defrost Cycle

In heating mode, a heat pump's outdoor coil can frost over. The system briefly reverses to melt it — you may see steam and hear a 'whoosh.' It's normal, automatic, and short. Learn more

Dehumidification

Removing moisture from indoor air. A correctly sized AC dehumidifies as it cools; an oversized one cools too fast to pull moisture out, leaving the house cold but clammy. Whole-home dehumidifiers handle the humid shoulder seasons. Learn more

Delta T (Temperature Split)

The difference between the air temperature going into your system and the cooled air coming out — typically around 16–22°F on a healthy AC. A low split can signal low refrigerant or airflow problems; a high split can signal restricted airflow.

Duct Leakage

Conditioned air escaping through gaps, bad connections, or holes in the duct system before it reaches your rooms. Leaky ducts in a hot attic waste a large share of what you pay to cool — sealing them is often the highest-payback comfort fix. Learn more

EER2

A rating of cooling efficiency at a single high outdoor temperature, rather than across a season. In a place with long, brutal summers like Central Texas, a strong EER2 (peak-heat efficiency) matters alongside the seasonal SEER2 number. Learn more

EPA Section 608 Certification

The federal certification required to legally handle refrigerant. It's why low refrigerant isn't a DIY fix — every MLD technician who touches refrigerant is EPA-certified. Learn more

Freon

A brand name people use as a catch-all for refrigerant. There's no single 'Freon' — your system uses a specific refrigerant such as R-410A or R-454B. 'Just add Freon' is a red flag, because low refrigerant means a leak that should be found and fixed. Learn more

Furnace

The appliance that heats air by burning fuel (usually natural gas) and blowing it through your ducts. Its efficiency is measured in AFUE, and its heat exchanger and flame-safety parts are the components you never want neglected. Learn more

Heat Exchanger

The part of a gas furnace that transfers heat from burning fuel into your home's air while keeping the combustion gases separate. A cracked heat exchanger is a safety issue (a carbon-monoxide risk) and usually means the furnace must be replaced. Learn more

Inverter / Variable-Capacity Compressor

A compressor that can ramp its output up and down instead of running flat-out or off. Inverter systems hold steadier temperatures, control humidity better, and use less energy — the technology behind most variable-speed equipment. Learn more

Line Set

The pair of insulated copper lines that carry refrigerant between your outdoor unit and indoor coil. On a full system replacement, the line set is inspected and sometimes replaced or flushed — especially when switching refrigerant types.

NATE Certification

North American Technician Excellence — an independent, industry-standard certification that proves an HVAC technician's knowledge through testing. It's one objective signal of a qualified installer or service tech. Learn more

Packaged Unit (RTU)

An all-in-one heating and cooling system in a single cabinet, often a rooftop unit (RTU) on commercial buildings. It contrasts with a split system, where the components live in separate indoor and outdoor units. Learn more

Plenum

The main air boxes attached to your air handler or furnace that distribute air into the supply ducts and collect it through the return. Leaky or poorly built plenums are a hidden source of lost airflow and efficiency. Learn more

Return & Supply Air

Supply vents blow conditioned air into your rooms; return grilles pull room air back to the system to be reconditioned. Too little return air (blocked grilles, undersized returns) is a common cause of weak airflow and frozen coils. Learn more

SEER (the original rating)

The older Seasonal Energy Efficiency Ratio, replaced by SEER2 in 2023. SEER2 uses a more realistic testing method, so a SEER2 number is slightly lower than the old SEER number for the same equipment — they aren't directly interchangeable. Learn more

Split System

The most common home setup: an outdoor unit (condenser/compressor) paired with an indoor unit (air handler or furnace + coil), connected by a refrigerant line set. 'Split' refers to the indoor/outdoor split of components. Learn more

Static Pressure

The resistance air meets as it moves through your ducts and filter — like blood pressure for your HVAC system. High static pressure (from undersized ducts, a too-restrictive filter, or closed vents) strains the blower and shortens equipment life. Learn more

TXV / Metering Device

The thermostatic expansion valve precisely meters refrigerant into the evaporator coil so the system cools efficiently across a range of conditions. A failing metering device causes poor cooling, icing, or short cycling.

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