HVAC Glossary

AFUE (Annual Fuel Utilization Efficiency)

A percentage that tells you how efficiently a furnace turns fuel into heat over a year. An AFUE of 95% means 95% of the fuel becomes usable heat and 5% is lost. Higher AFUE means lower heating bills.

Air Conditioner (Central)

A split system that cools your whole home through ductwork, using an outdoor condenser and an indoor evaporator coil. It removes both heat and humidity; pair it with a furnace or air handler for year-round comfort. How long does an AC last?

Air Handler

The indoor unit that moves conditioned air through your ductwork. In a heat pump or electric system it pairs with the outdoor unit; it contains the blower and the indoor (evaporator) coil.

Auxiliary / Emergency Heat

Backup heat built into a heat pump system — usually electric resistance strips — that kicks in on the coldest days or if the heat pump needs help. 'Emergency heat' is the manual setting that runs backup only; it's less efficient, so use it sparingly. Heat pumps in KY winters

Balance Point

The outdoor temperature at which a heat pump can no longer cover 100% of your home's heat loss on its own, so backup or a gas furnace takes over. It's set during installation based on your home and equipment. Dual-fuel heating explained

BTU (British Thermal Unit)

The basic unit of heating and cooling capacity. One ton of cooling equals 12,000 BTU per hour. The correct BTU capacity for your home comes from a load calculation, not a guess. What size HVAC do I need?

Capacitor

A small electrical component that gives the AC or furnace motor the jolt it needs to start and keep running. A failed capacitor is one of the most common — and most affordable — HVAC repairs, often the reason a system hums but won't start. Why is my AC blowing warm air?

CFM (Cubic Feet per Minute)

A measure of airflow — how much air your system moves per minute. Correct CFM matters as much as capacity: too little airflow causes frozen coils and poor comfort, which is why duct design (Manual D) is part of a proper install.

Compressor

The heart of an AC or heat pump, located in the outdoor unit. It pressurizes refrigerant so the system can move heat. A failed compressor is a major repair and is often the moment to weigh replacing an older system. Why is my AC freezing up?

Condensate Drain Line

The pipe that carries the water your AC pulls out of the air to a drain. A clogged condensate line is a common cause of water leaks and shut-offs, especially in humid Kentucky summers — clearing it is a routine maintenance task. AC maintenance checklist

Condenser

The outdoor unit of a split system. In cooling mode it releases heat pulled from inside your home; in a heat pump it also absorbs outdoor heat during winter to warm the house.

COP (Coefficient of Performance)

A measure of a heat pump's heating efficiency — the ratio of heat delivered to energy used. A COP above 1 means the system moves more heat energy than the electricity it consumes, which is why heat pumps can be so efficient. How a heat pump works

Defrost Cycle

A normal heat-pump function in cold, damp weather: the unit briefly reverses to melt frost off the outdoor coil, which pauses warm air for a few minutes. It's the system protecting itself, not a breakdown. Heat pumps in KY winters

Dehumidifier (Whole-House)

Equipment that removes moisture from the whole home, integrated with the HVAC system. In humid Kentucky, it helps when a properly sized AC alone can't keep indoor humidity comfortable, protecting against that clammy, musty feeling. Do you need a dehumidifier?

Dual-Fuel (Hybrid) System

A heat pump paired with a gas furnace. The efficient heat pump handles most of the season and the furnace takes over below the balance point on the coldest days — often the most efficient, comfortable setup for a Kentucky home. Dual-fuel heating explained

Ductless Mini-Split

A heating and cooling system with no central ductwork. An outdoor unit connects to one or more wall- or ceiling-mounted indoor heads, making it ideal for additions, garages, and homes without ducts. Heat pump & mini-split costs

Ductwork

The network of channels that distributes heated and cooled air through your home. Leaky, undersized, or poorly designed ducts waste energy and hurt comfort; duct design (Manual D) is part of sizing a system correctly. Sizing your system

EER2 (Energy Efficiency Ratio 2)

A measure of cooling efficiency at a single high-temperature condition, updated alongside SEER2 in 2023. Where SEER2 reflects a whole season, EER2 reflects performance on the hottest days — useful in hot, humid climates like Kentucky's. What is SEER2?

ENERGY STAR

A U.S. EPA program that certifies higher-efficiency equipment. ENERGY STAR-rated HVAC systems meet efficiency thresholds above the federal minimum and often qualify for rebates and incentives. Rebates & savings

Evaporator Coil

The indoor coil where refrigerant absorbs heat and humidity from your home's air. A dirty or frozen evaporator coil is a common reason an AC blows warm air. Why is my AC blowing warm air?

Filter (Air Filter)

The replaceable media that traps dust and particles before air enters your system. A clogged filter is the #1 cause of airflow problems, frozen coils, and avoidable breakdowns — check it every 30–90 days. (See also MERV.) AC maintenance checklist

Furnace

A heating system that burns gas (or uses electricity) to warm air, then distributes it through ductwork. Gas-furnace efficiency is measured by AFUE; a cracked heat exchanger is a safety reason to replace one. How long does a furnace last?

Heat Exchanger

The component in a furnace that transfers combustion heat to your home's air while keeping exhaust gases separate. A cracked heat exchanger can leak carbon monoxide, so it's a safety issue that typically means furnace replacement. Furnace blowing cold air?

Heat Pump

A single system that both heats and cools by moving heat rather than burning fuel. It pulls heat out of your home in summer and pulls heat from outdoor air into your home in winter, which makes it very efficient in Kentucky's climate. How much does a heat pump cost?

HSPF2 (Heating Seasonal Performance Factor 2)

The current efficiency rating for a heat pump's heating mode. Like SEER2 for cooling, a higher HSPF2 means more heat delivered per unit of electricity.

Humidifier (Whole-House)

Equipment that adds moisture to dry winter air through the HVAC system. It's the opposite of a dehumidifier; in Kentucky, summer humidity control is usually the bigger concern, but very dry winter heat can warrant one. Managing home humidity

Indoor Air Quality (IAQ)

How clean and healthy the air inside your home is — affected by filtration, humidity, ventilation, and contaminants like dust, pollen, mold, and odors. HVAC add-ons such as media filters, UV lights, and purifiers target different IAQ problems. Indoor air quality services

Inverter / Variable-Speed

Technology that lets a compressor or blower run at many speeds instead of just on or off. Inverter systems hold temperature steadily, run quietly, and use less energy than older single-stage equipment.

Latent vs. Sensible Heat

Sensible heat is the temperature you feel on a thermostat; latent heat is the moisture (humidity) in the air. A good AC removes both — important in humid Kentucky, where an oversized system cools fast but leaves the air clammy. Reducing home humidity

Load Calculation (Manual J)

The industry-standard method (ACCA Manual J) for determining exactly how much heating and cooling a home needs. It accounts for square footage, insulation, windows, orientation, air leakage, and climate — the right way to size a system. Manual J explained

Manual D & Manual S

The ACCA companions to Manual J: Manual D designs the ductwork to deliver the right airflow to each room, and Manual S selects equipment that matches the load. Together they make sure a correctly sized system actually performs. Manual J explained

MERV (Minimum Efficiency Reporting Value)

A 1-20 scale rating how well an air filter captures particles. Most homes do well with MERV 8-13; higher isn't always better, because a filter that's too restrictive can strain a system not designed for it. Filtration, UV & purifiers

NATE Certified

North American Technician Excellence (NATE) is an independent certification for HVAC technicians, earned by passing knowledge exams. It's one signal of a tech's training, alongside state licensing and EPA Section 608 certification.

Plenum

The central air distribution box that connects to your air handler or furnace, where conditioned air gathers before entering the supply ducts (and returns from the home). Proper plenum and duct design keeps airflow balanced.

R-410A

The refrigerant used in most central AC and heat pump systems sold from the early 2000s through 2024. It is being phased down in favor of lower-global-warming refrigerants.

R-454B / R-32 (A2L Refrigerants)

Lower-global-warming-potential refrigerants that began replacing R-410A in new residential systems in 2025. Daikin equipment uses R-32. New installs use these next-generation refrigerants. The 2025 refrigerant change

Refrigerant

The fluid that cycles through your AC or heat pump, absorbing heat indoors and releasing it outdoors (and the reverse for heat-pump heating). Handling refrigerant requires EPA Section 608 certification, which DuctPros technicians hold.

Relative Humidity (RH)

The percentage of moisture in the air relative to what it can hold at that temperature. Most homes are comfortable around 45–55% RH; in humid Kentucky, keeping RH in that range is as important to comfort as the temperature itself. Reduce home humidity

Return & Supply Air

Supply air is the conditioned air your system delivers to rooms; return air is the air pulled back to be reconditioned. Balanced return and supply airflow is essential for comfort and efficiency — blocked returns are a common comfort complaint.

SEER2 (Seasonal Energy Efficiency Ratio 2)

The current rating for an air conditioner's or heat pump's cooling efficiency, updated from the older SEER standard in 2023. A higher SEER2 means lower cooling bills; Daikin offers systems up to 24 SEER2. AC replacement cost

Short Cycling

When a system turns on and off too frequently without completing a full cooling or heating cycle. It wears out parts, wastes energy, and often signals an oversized system, low refrigerant, or a control problem.

Static Pressure

The resistance to airflow inside your duct system, like blood pressure for your HVAC. High static pressure — from undersized ducts, dirty filters, or closed vents — strains the blower, wastes energy, and shortens equipment life.

Thermostat (Programmable / Smart)

The control that tells your system when to heat or cool. Programmable and smart thermostats save energy with schedules and setbacks, and are especially useful for cabins or vacation rentals where you manage comfort remotely. HVAC for cabins & rentals

Ton / Tonnage

A measure of cooling capacity — one ton equals 12,000 BTU per hour. Most homes need between 1.5 and 5 tons; the right tonnage comes from a Manual J load calculation, not square footage alone. Sizing your system

Tune-Up (Preventive Maintenance)

A scheduled inspection and cleaning that keeps a system efficient and catches small problems before they become breakdowns. DuctPros offers Platinum and Silver maintenance plans that include seasonal tune-ups. Maintenance plans

Two-Stage / Single-Stage

Describes how a furnace or AC runs. Single-stage is full-blast on/off; two-stage adds a gentler low setting for milder days; variable-capacity (inverter) fine-tunes output continuously. More stages mean steadier comfort and better humidity control. Efficiency & SEER2

UV Light (Germicidal UV)

An ultraviolet lamp installed in the HVAC system to reduce mold and bacteria growth on the coil and in the air stream. It helps with biological contaminants but does not capture dust or pollen the way a filter does. Do I need a UV light?

Zoning

A system of dampers and thermostats that lets you heat or cool different areas of a home independently, so you're not paying to condition rooms you aren't using. Ductless mini-splits are zoned by design, with a head per area. Mini-split vs. central air

Ready to put these terms to use? Start with our HVAC Learning Center or request a free estimate.