HVAC Resource
HVAC Definitions and Air Conditioning Terms
Plain-English HVAC definitions for air conditioning, heating, airflow, refrigerant, electrical parts, maintenance, and service calls.
A practical HVAC glossary
HVAC terms come up during service calls, estimates, maintenance, repair decisions, and equipment replacement. Clear definitions make those details easier to understand without turning them into a textbook.
Some terms are simple. Others need more detail because the measurement, part, or system condition affects what a technician is testing.
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If a term on this page connects to a real cooling, heating, water, or electrical problem, call for service.
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A
Accumulator
A component in the suction line that helps keep liquid refrigerant from entering the compressor. Compressors are made to pump vapor, not liquid.
AFUE
Annual Fuel Utilization Efficiency. It measures how much of the fuel used by a furnace becomes usable heat. A higher AFUE number means less wasted fuel.
Air Balance
The process of checking and adjusting airflow so rooms receive the right amount of supply air and the system can move air correctly.
Air Conditioner
A cooling system that removes heat from indoor air and moves that heat outside. A central air conditioner also removes some moisture while it runs.
Air Filter
A filter in the return-air path that catches dust and debris before air reaches the blower and indoor coil. A dirty filter can reduce airflow and cause cooling problems.
Air Handler
The indoor part of some HVAC systems. It usually contains the blower, evaporator coil, controls, and sometimes electric heat strips.
Air Purifier
An indoor air quality accessory installed with the HVAC system to help reduce certain airborne particles. The equipment, duct layout, airflow, access, and customer goal should be checked first.
Airflow
The movement of air through the return, filter, blower, coil, ductwork, and supply registers. Many AC problems start with weak or blocked airflow.
Angle Stop
A small shutoff valve, often located under a sink or toilet, that controls water to a fixture. If it is frozen, corroded, or leaking, fixture work can become more involved.
Auxiliary Heat
Backup or supplemental heat used by some heat pump systems when the heat pump needs help keeping up or when system controls call for additional heat.
B
Belt Drive
A motor-and-belt arrangement used on some commercial HVAC blowers. Belt wear, tension, alignment, and pulley condition can affect airflow and noise.
Blower Motor
The motor that moves indoor air through the filter, coil, ductwork, and supply vents. A weak or failed blower can cause low airflow, frozen coils, or no air from the vents.
Blower Wheel
The rotating wheel or squirrel-cage fan moved by the blower motor. Dust buildup, rubbing, damage, or wheel problems can reduce airflow even when the motor still runs.
Breaker Trip
When a circuit breaker opens and shuts off power because the circuit is drawing too much current or has a fault. Repeated trips should be diagnosed instead of reset over and over.
BTU
British Thermal Unit. HVAC systems use BTUs to describe heating or cooling capacity. One ton of cooling equals 12,000 BTUs per hour.
Building Automation
A control system that can schedule, monitor, or coordinate HVAC equipment in a commercial building. Large automation issues may require specialized controls support.
C
Capacitor
An electrical component that helps a motor start or run. Outdoor fans, compressors, and blower motors often use capacitors. A weak capacitor can stop a motor from starting correctly.
Capacity
How much heating or cooling a system can produce. Cooling capacity is often described in tons, while heating capacity is often described in BTUs.
Carbon Monoxide
An odorless and dangerous gas that can be produced by fuel-burning equipment when combustion or venting is unsafe. Carbon monoxide problems should be treated seriously.
CFM
Cubic feet per minute. This is a measurement of airflow volume. HVAC technicians use CFM to evaluate blower output, ductwork, and comfort problems.
Check Valve
A valve that allows flow in one direction and helps prevent reverse flow. Pool equipment pads and plumbing systems may use check valves depending on the layout.
Chiller
A cooling machine that removes heat from water or another fluid. Chillers are more common in larger commercial buildings than in typical homes.
Circuit Breaker
An electrical safety device that opens a circuit when current is too high. If a breaker trips repeatedly, the cause should be checked instead of resetting it over and over.
Closet Bolts
Bolts that help hold a toilet to the flange at the floor. Loose, corroded, or damaged closet bolts can let a toilet move and may compromise the wax seal.
Coil
A heat-transfer surface in an HVAC system. The evaporator coil absorbs heat indoors, and the condenser coil releases heat outdoors.
Common Wire
The thermostat wire, often labeled C, that provides a common side of low-voltage power for many digital and smart thermostats. Not every older thermostat cable has one.
Compressor
The part of an air conditioner or heat pump that pumps refrigerant through the system. It raises refrigerant pressure and keeps the cooling cycle moving.
Condensate Drain
The drain line that carries water away from the indoor coil area. If it clogs, water can back up, overflow, or trip a float switch.
Condensate Pan
A pan under the evaporator coil that catches water produced during cooling. The water should leave through the condensate drain.
Condenser Coil
The outdoor coil that releases heat from the refrigerant to the outside air. Dirty condenser coils can raise pressure and reduce cooling performance.
Condenser Fan
The outdoor fan that moves air through the condenser coil. If this fan fails, the outdoor unit may overheat or stop cooling.
Condenser Fan Motor
The outdoor motor that turns the condenser fan blade. If it fails, the outdoor unit may hum, overheat, trip, or stop rejecting heat correctly.
Conduit
A protective tube or raceway used to route electrical wiring. Outdoor HVAC wiring may use flexible conduit between the disconnect and equipment.
Contactor
An electrical switch inside the outdoor unit that sends power to the compressor and condenser fan when the thermostat calls for cooling.
Control Board
An electronic board that controls or coordinates HVAC operation. Boards may manage blower timing, safety circuits, defrost, ignition, or communication between components.
Copper Pipe
A metal plumbing pipe commonly used for water lines and equipment connections. Copper repairs depend on access, condition, corrosion, and nearby fittings.
CPVC
Chlorinated polyvinyl chloride. CPVC is a plastic pipe material used in some water piping systems and requires repair methods compatible with the material and condition.
Cycling
The normal process of a system turning on, running, and turning off. Short cycling means the system turns on and off too quickly.
D
Damper
A device inside ductwork that can open or close to control airflow. Dampers are often used for balancing air or zoning.
Defrost Cycle
A heat pump operating mode that melts frost from the outdoor coil during heating operation. Defrost problems can affect heating performance and comfort.
Diffuser
A supply-air outlet designed to spread air into a room. Diffusers help direct air instead of dumping it straight out of a duct.
Digital Thermostat
A thermostat with electronic controls. Some are basic, some are programmable, and some connect to Wi-Fi or smart-home systems.
Disconnect
The electrical shutoff near HVAC equipment. It allows power to be disconnected for service or emergency shutdown.
Dishwasher Drain Hose
The hose that carries dishwasher discharge water into a disposal, air gap, or drain connection. A loose, misaligned, or poorly connected hose can leak or drain poorly.
Diverter Valve
A valve used to direct water flow between different paths. Pool systems may use diverter valves for suction, return, spa, cleaner, or water-feature routing.
Door Switch
A safety switch on some indoor HVAC cabinets that can stop blower or equipment operation when an access panel is removed or not seated correctly.
Downflow Furnace
A furnace that takes return air from the top and sends heated air downward. The correct furnace style depends on the duct layout and installation location.
Drain Assembly
The drain parts connected to a sink, tub, or fixture. A drain assembly may include a strainer, pop-up, tailpiece, trap, washers, nuts, and connecting piping.
Drain Cleanout
An access point that helps a technician clear or verify a drain line. On an HVAC condensate drain, cleanout access can make drain service easier and more reliable.
Drain Pan
A pan that catches water near the evaporator coil or under equipment. Drain pans help protect your home if water forms or backs up.
Drain Slope
The pitch of drain piping that helps water move away from equipment. Poor slope can leave water sitting in the line and make clogs more likely.
Drain Trap
A shaped section of condensate drain piping that helps the HVAC drain work with the equipment airflow and pressure. Poor trap layout can contribute to drainage problems.
Duct Cleaning
A service that removes debris from duct interiors when it helps solve the problem. Duct cleaning cannot fix filter bypass, duct leaks, dirty coils, or airflow problems.
Duct Leakage
Air escaping from supply ducts or being pulled into return ducts through gaps, loose connections, damaged ductwork, or poorly sealed fittings.
Duct Repair
Repair work on damaged, disconnected, torn, loose, or leaking duct sections, boots, fittings, or connections when access and duct condition support repair.
Duct Replacement
Replacing duct sections or larger duct systems when ducts are badly damaged, undersized, deteriorated, poorly routed, or part of a larger comfort or installation project.
Duct Sealing
Sealing duct joints, seams, takeoffs, boots, or fittings to reduce air leakage when the duct condition and access support sealing.
Duct Takeoff
The connection where a branch duct leaves a plenum, trunk duct, or transition. Poor takeoffs can reduce airflow to specific rooms or duct runs.
Ductless Mini-Split
A heating and cooling system that serves a room or zone without traditional ductwork. Mini-splits are often used for additions, garages, offices, or difficult-to-duct spaces.
Ductwork
The duct system that carries return air back to the equipment and supply air out to the rooms. Duct leaks, restrictions, and poor sizing can hurt comfort.
E
ECM
Electronically commutated motor. ECM blower motors can run at different speeds and are often more efficient than older motor designs.
Economizer
A control and damper system on some commercial HVAC units that can use outdoor air for cooling when conditions are right. Economizer problems can affect comfort and controls.
Electric Water Heater
A water heater that uses electric heating elements and thermostats to heat stored water. Electrical power, wiring, elements, thermostats, and tank condition all matter during diagnosis.
Electrical Whip
The flexible conduit and wiring that carries power from the disconnect to the outdoor HVAC unit. A damaged whip can create unsafe power problems.
Electronic Air Cleaner
An indoor air quality device that uses an electrical charge to help remove particles from the air. It may require cleaning and maintenance.
Emergency Drain Pan
A secondary pan installed under some HVAC equipment to catch overflow if the primary drain pan or condensate drain has a problem. It should not hold water during normal operation.
Energy Star
A label used for equipment that meets efficiency standards set by government programs. It is one way to compare equipment efficiency.
Equipment Pad
The area where outdoor pool equipment, HVAC equipment, or plumbing equipment is installed. Pool equipment pads often include pumps, filters, valves, unions, and exposed PVC piping.
Evaporator Coil
The indoor coil that absorbs heat from the air. A dirty, frozen, or restricted evaporator coil can cause weak cooling, water leaks, and airflow problems.
Expansion Tank
A small tank used on some water heater systems to absorb pressure changes as water heats and expands. Whether one is needed depends on the plumbing setup and code requirements.
Expansion Valve
A metering device that controls refrigerant flow into the evaporator coil. TXV is a common type of expansion valve.
F
Fan Coil
An indoor coil and blower assembly, often used with heat pumps or chilled-water systems. It moves air across a coil to heat or cool the space.
Faucet Cartridge
A replaceable part inside many faucets that controls water flow and temperature. A worn cartridge can cause dripping, poor control, or leaks around the handle.
Fill Valve
A toilet tank part that refills the tank after a flush and shuts off when the water reaches the correct level. A bad fill valve can cause running, slow refill, or noise.
Filter
A removable filter in the return-air path that catches dust before air reaches the blower and coil. Dirty, missing, or poorly fitted filters can reduce airflow and let debris into the system.
Filter Bypass
Air moving around a filter instead of through it. Filter bypass can let dust into the blower, coil, and duct system even when a filter is installed.
Filter Drier
A refrigerant-circuit part that helps catch moisture and debris. A restricted filter drier can affect refrigerant flow and system readings.
Fixture
A plumbing device such as a faucet, sink, toilet, shower valve, or utility sink that uses or controls water. Fixture repairs often depend on access, parts, shutoff valves, and surrounding plumbing.
Flame Sensor
A furnace safety sensor that proves burner flame is present. A dirty or failed flame sensor can cause a furnace to start and then shut back down.
Flapper
A rubber or plastic toilet tank part that seals water in the tank until the toilet is flushed. A worn flapper can let water leak into the bowl and make the toilet run.
Flex Connector
A flexible connector used to connect water heaters, fixtures, or equipment to plumbing. Connectors should be matched to the application and replaced if kinked, corroded, leaking, or damaged.
Flex Duct
Flexible insulated duct used for many residential attic runs. Crushed, sagging, kinked, or poorly supported flex duct can restrict airflow.
Float Switch
A safety switch that can shut the system off when condensate water rises too high. It helps prevent water damage from a clogged drain.
Freon
A common name people use for refrigerant. Freon is technically a brand name, but many people use it to mean the refrigerant in an AC system.
Frozen Coil
Ice forming on the evaporator coil or refrigerant line. A frozen coil is a symptom that can involve airflow restrictions, dirty filters, dirty coils, blower problems, refrigerant conditions, or drainage concerns after thawing.
Furnace
Heating equipment that warms air and sends it through ductwork. Furnaces may use gas, propane, oil, or electricity depending on the system.
Fuse
An electrical protection device that opens when current is too high. In a fused AC disconnect, a failed fuse can stop the outdoor unit, but the cause still needs to be checked.
Fused Disconnect
An outdoor service disconnect that contains fuses. It can shut off power near the equipment and also protect the outdoor circuit with replaceable fuses.
G
Galvanized Pipe
Steel pipe coated with zinc. Older galvanized piping can corrode, restrict flow, and be harder to repair cleanly than newer piping materials.
Garbage Disposal
An under-sink appliance that grinds food waste before it enters the drain piping. Disposal problems can involve jams, leaks, mounting, drain connections, dishwasher connections, power, or internal failure.
Gas Water Heater
A water heater that uses gas combustion to heat water. Gas supply, burner operation, controls, clearances, and venting need to be checked carefully.
H
Hard Start Kit
A start-assist device that can help a compressor start under certain conditions. It cannot solve every compressor or capacitor problem.
Heat Exchanger
A furnace component that transfers heat from combustion to the air stream while keeping combustion gases separated from indoor air. Heat exchanger concerns are safety-sensitive.
Heat Pump
A system that can move heat in either direction. It cools like an air conditioner in summer and can provide heat in cooler weather.
Heat Transfer
The movement of heat from one place to another. In cooling mode, the evaporator coil absorbs heat indoors and the condenser coil releases heat outdoors.
Horizontal Flow
An equipment layout where air enters one side and leaves the other side. This style is common in some attic and crawlspace installations.
Hose Bib
An exterior faucet used for hoses. A hose bib can leak, loosen, corrode, or fail at the wall connection, handle, packing, or nearby piping.
HSPF
Heating Seasonal Performance Factor. It measures heat pump heating efficiency. Higher numbers indicate better heating efficiency.
Humidifier
A device that adds moisture to indoor air. Humidifiers are more common in dry heating climates than in many Phoenix cooling applications.
HVAC
Heating, ventilation, and air conditioning. HVAC covers the equipment and airflow systems used to heat, cool, ventilate, and condition indoor air.
I
Ignition Sequence
The ordered startup process a furnace follows before burners operate. It may include inducer operation, pressure switch proof, ignitor operation, gas valve opening, flame sensing, and blower timing.
Ignitor
A furnace part that lights the burners during the heating startup sequence. Ignitor problems can keep a furnace from producing heat.
Indoor Air Quality
A broad term for filtration, ventilation, humidity, dust, odors, duct condition, and other comfort or air-cleanliness concerns inside a building.
L
Limit Switch
A furnace safety switch that can stop burner operation if the equipment gets too hot or airflow is not moving correctly.
Load Calculation
A calculation used to estimate how much heating or cooling a building needs. It considers size, insulation, windows, orientation, climate, and other details.
Locked Rotor
A motor or compressor condition where the rotor cannot turn normally during startup. It can create high current draw and may trip a breaker or overload protection.
Louver
An opening with angled blades that controls or directs airflow. Louvers may be used for vents, grilles, or outdoor equipment openings.
Low-Voltage Fuse
A small fuse in the HVAC control circuit. If it blows, the thermostat, control board, contactor signal, or other low-voltage controls may stop responding until the cause is found.
Low-Voltage Wiring
Small control wiring that carries thermostat and HVAC control signals. Loose, shorted, damaged, or miswired low-voltage wiring can stop equipment from responding.
Lug
A metal terminal or connector where an electrical wire is secured. Loose lugs can overheat, damage wiring, and create intermittent power problems.
M
Main Line
The main drain or sewer path that carries wastewater away from a home or building. Main-line stoppages usually need larger drain service than a fixture-drain leak.
Make-Up Air
Outdoor air brought into a building to replace air removed by exhaust systems, such as kitchen hoods. Make-up air affects comfort, pressure, and restaurant HVAC performance.
Matched System
Indoor and outdoor equipment designed to work together at a rated capacity and efficiency. Mismatched equipment can hurt performance and warranty coverage.
Metering Device
The part of the refrigerant circuit that controls refrigerant flow into the evaporator coil. Metering problems can affect cooling, pressure readings, and coil temperature.
MFD
Microfarad. This is the rating used on many HVAC capacitors. The replacement capacitor must match the required MFD rating.
N
Natural Gas
A fuel commonly used for furnaces, gas package units, and water heaters. Gas equipment must be installed and vented correctly.
O
Operating Cost
The cost to run HVAC equipment. Operating cost depends on efficiency, equipment condition, thermostat settings, home load, energy rates, and run time.
Overcharge
A condition where an AC system has too much refrigerant. Overcharge can cause poor cooling, abnormal pressures, and compressor stress.
P
P-Trap
A curved drain fitting under a sink or fixture that holds water to block sewer gas from coming back through the drain. Trap leaks are diagnosed differently than pressurized supply leaks.
Package Unit
An HVAC system that contains the heating and cooling sections in one cabinet. Package units are often installed on rooftops in Arizona.
Payback Analysis
A comparison of equipment cost and estimated energy savings. It helps estimate how long efficiency savings may take to offset a higher purchase price.
PEX
Cross-linked polyethylene. PEX is a flexible plastic water piping material that uses fittings and connection methods specific to the system type.
Plenum
A box or chamber connected to HVAC equipment where air collects before moving into ducts or returning from the duct system.
Pool Pump
A pump that circulates pool water through the pool equipment. Plumbing around a pool pump can include suction lines, return lines, unions, valves, fittings, and equipment-pad piping.
Pop-Up Drain
A bathroom sink drain assembly with a stopper controlled by a lift rod or linkage. Pop-up drains can leak, stick, drain slowly, or stop sealing correctly.
Primary Drain Pan
The pan built into or directly below the evaporator coil area that handles normal AC condensate and directs it into the condensate drain.
Pump Lid O-Ring
A seal under the pool pump lid. If it is dirty, dry, cracked, or out of place, it can let air into the pump and contribute to priming problems.
PVC Fitting
A plastic pipe fitting used to connect PVC pipe sections, valves, unions, and equipment. Exposed pool PVC fittings can crack, leak, or become brittle from age and sun exposure.
R
R-22 Refrigerant
An older refrigerant used in many older AC systems. New production and import for R-22 ended in 2020, but recovered and reclaimed refrigerant can still be used to service existing systems when repair makes sense.
R-32 Refrigerant
A newer lower-GWP refrigerant used in some modern air conditioning equipment. It is mildly flammable and requires proper equipment and handling.
R-410A Refrigerant
A refrigerant used in many systems installed after R-22. It is now being phased down in new equipment as newer refrigerants enter the market.
R-454B Refrigerant
A newer lower-GWP refrigerant used in some new HVAC equipment. Like R-32, it is mildly flammable and requires proper service practices.
Recirculation Pump
A pump used on some plumbing systems to move hot water through a loop so fixtures receive hot water more quickly. Piping layout, check valves, controls, and water heater connections affect how it works.
Refrigerant
The fluid inside an air conditioner or heat pump that absorbs and releases heat as it changes pressure and state. It should not be treated like a consumable fuel.
Refrigerant Charge
The amount of refrigerant in an AC system. The correct charge depends on system design, refrigerant type, airflow, metering, and diagnostic readings.
Refrigerant Leak
A leak in the sealed refrigerant circuit. Leak symptoms can overlap with airflow, coil, blower, and outdoor-unit problems, so readings and system conditions should be checked.
Refrigerant Lines
Copper lines that carry refrigerant between the indoor and outdoor sections of a split system. One line is usually larger and insulated.
Refrigeration-Adjacent
Commercial work near refrigeration, kitchen, or process equipment where HVAC symptoms may overlap with specialized refrigeration needs. Some issues may require a refrigeration specialist.
Register
A room air opening with a grille or adjustable damper. Registers deliver supply air or pull return air depending on the duct connection.
Relay
An electrical switch controlled by a smaller control signal. HVAC boards and control circuits may use relays to turn motors, blowers, or other equipment on and off.
Repipe
A larger plumbing project that replaces substantial sections of water piping, sometimes across a whole home or building. It is a larger project than a exposed pipe repair.
Return Air
Indoor air pulled back to the equipment to be filtered, cooled or heated, and sent out again through the supply ducts.
Return Duct
The duct path that carries return air back to the HVAC equipment. A restricted return duct can reduce airflow and performance.
Return Grille
The room or hallway grille where air returns to the HVAC system. Blocked, undersized, dirty, or poorly located return grilles can reduce airflow.
Return Plenum
The return-side chamber or box where return air collects before entering the equipment, filter, blower, or coil area. A poor return plenum can restrict airflow or pull in dusty air.
Return-Side Leak
A leak on the pressure side after a pump is pushing water through the system. Return-side pool leaks may spray or drip only when the pump is running.
Reversing Valve
A heat pump valve that changes refrigerant flow direction so the system can switch between cooling and heating modes.
Roof Curb
A roof-mounted frame or support that connects a rooftop HVAC unit to the roof opening and duct system. Curb fit can matter during commercial replacement.
Rooftop Unit
HVAC equipment installed on a roof. Many commercial systems and some residential package units are rooftop units.
Room Pressure
The pressure difference created when supply air enters a room but return air cannot leave properly. Closed doors and poor return paths can affect room pressure.
Rough-In
The measured distance from the finished wall to the center of a toilet drain or other plumbing connection. Toilet replacement depends on matching the rough-in size.
Run Capacitor
A capacitor that helps a motor run efficiently after it starts. Some systems use dual run capacitors for both the compressor and fan motor.
S
Safety Switch
A switch that can stop equipment operation when an unsafe or damaging condition is present, such as a panel being open or condensate water rising too high.
Scroll Compressor
A compressor design that uses two scroll-shaped pieces to compress refrigerant. Scroll compressors are common in many modern HVAC systems.
Secondary Drain Pan
An emergency pan under or near HVAC equipment that can catch water if the primary drain or pan overflows. Water in the secondary pan means the source should be checked.
SEER
Seasonal Energy Efficiency Ratio. It is an older efficiency rating used to compare cooling efficiency over a season. Higher SEER usually means better efficiency.
SEER2
The newer cooling efficiency rating system that replaced SEER for new equipment ratings. SEER2 uses updated test conditions.
Setback Thermostat
A thermostat that can automatically change set points at different times of day. Programmable thermostats are a common example.
Sewer Backup
Wastewater backing up from a sewer or main drain problem. Sewer backups should be treated as a larger drain issue and may require a specialist.
Short Cycling
A condition where the system starts and stops too often. It can be caused by airflow problems, controls, refrigerant issues, sizing, or safety switches.
Shutoff Valve
A valve used to stop water to a fixture or piece of equipment. Fixture work can depend on whether the shutoff valve closes fully and does not leak.
Sink Flange
The ring at the sink opening where a garbage disposal or drain assembly mounts. A loose, corroded, or poorly sealed flange can leak into the cabinet below.
Slab Leak
A water leak under or inside a concrete slab foundation. Slab leaks often require specialized leak detection, access details, rerouting, or larger plumbing work.
Slip Joint
A compression-style connection often used on tubular drain piping under sinks. Slip joints can leak if the washer is worn, the nut is loose, or the piping is misaligned.
Smart Thermostat
A connected thermostat with digital controls and often Wi-Fi features. It still has to match the HVAC wiring, equipment type, common-wire needs, and system setup.
Split System
An HVAC system with indoor and outdoor sections connected by refrigerant lines. Most central air conditioners and heat pumps are split systems.
Start Capacitor
A capacitor used to help a motor or compressor start. It is usually only in the circuit briefly during startup.
Static Pressure
Resistance to airflow inside the HVAC system. Dirty filters, closed registers, blocked returns, restrictive ducts, or dirty coils can raise static pressure.
Subcooling
A refrigerant measurement that compares liquid refrigerant temperature to its saturation temperature. It helps evaluate charge and metering performance.
Suction-Side Leak
A leak before a pump where air can be pulled into the system. In pool plumbing, suction-side leaks can cause air in the pump basket, bubbles, noise, or loss of prime.
Superheat
A refrigerant measurement that compares vapor refrigerant temperature to its saturation temperature. It helps evaluate evaporator performance and refrigerant feed.
Supply Duct
The duct path that carries cooled or heated air from the equipment to the rooms. Supply restrictions can cause comfort and airflow problems.
Supply Line
A water line that carries pressurized water to a fixture, toilet, water heater, or appliance. Supply-line leaks can continue even when the fixture is turned off.
Supply Plenum
The supply-side chamber or box where conditioned air leaves the equipment before entering the supply ducts. A poor supply plenum can restrict or unevenly distribute airflow.
Supply Register
A room grille or outlet that delivers conditioned supply air from the duct system into the room. Location, direction, damper position, and duct connection affect airflow.
T
T&P Discharge
The piping connected to a water heater temperature and pressure relief valve. It should be routed correctly and should not be capped, blocked, or ignored if it discharges.
T&P Valve
Temperature and pressure relief valve. This safety valve is designed to discharge if water heater temperature or pressure becomes unsafe. It should not be capped or blocked.
Tailpiece
A vertical drain pipe section below a sink drain or fixture outlet. Tailpieces connect the fixture drain to the trap or other drain fittings.
Tankless Water Heater
A water heater that heats water as it flows through the unit instead of storing hot water in a tank. Sizing, fuel supply, venting, service access, and water quality all affect performance.
Temperature Rise
The temperature difference between return air entering a heating system and supply air leaving it. It helps evaluate heating performance and airflow.
Temperature Split
The temperature difference between return air entering the system and supply air leaving the system. It is one clue technicians use during cooling diagnostics.
Tenant Space
A leased commercial area served by its own HVAC equipment or shared building systems. Service often depends on tenant access, landlord approval, and property-manager communication.
Thermal Zone
An area of a building with similar heating and cooling needs. Zoning systems can control separate thermal zones.
Thermostat
The control that senses temperature and tells the HVAC system when to heat, cool, or stop. Thermostat problems can look like equipment problems.
Toilet Flange
The floor-mounted fitting that connects a toilet to the drain and gives the toilet a fastening point. A damaged, low, or loose flange can cause base leaks or a wobbly toilet.
Ton
A cooling capacity measurement. One ton of cooling equals 12,000 BTUs per hour. Residential systems are often described by tonnage.
Transformer
An electrical component that steps voltage down for the HVAC control circuit. Thermostats, control boards, contactors, and safety switches often depend on transformer power.
Transition
A duct fitting that changes air from one opening size or shape to another. Poor transitions can restrict airflow, leak air, or create turbulence.
Trap Arm
The drain pipe section that connects a P-trap to the wall or downstream drain piping. Trap-arm alignment and slope can affect drainage and leak risk.
Two-Stage Air Conditioner
An air conditioner with low and high cooling stages. Two-stage systems can run longer at lower output for better comfort and humidity control.
TXV
Thermostatic expansion valve. A TXV meters refrigerant into the evaporator coil based on system conditions.
U
Underfloor Air Distribution
A commercial air distribution method that supplies conditioned air through a raised floor area. Typical residential systems rarely use it.
Union
A fitting that allows piping or equipment to be disconnected without cutting pipe. Pool pump plumbing often uses unions at pump, valve, or equipment connections.
Upflow Furnace
A furnace that pulls return air from the bottom and sends heated air out of the top.
UV Light
An indoor air quality accessory that uses ultraviolet light near HVAC equipment or ductwork. Fit, access, electrical needs, airflow, and maintenance requirements should be checked.
V
Variable Air Volume
A commercial HVAC approach that changes airflow volume to match the needs of a space or zone. It is often called VAV.
Ventilator
A device that brings in outdoor air or exchanges indoor air with outdoor air. Ventilation equipment must be matched to the building and climate.
Venting
The path that carries combustion gases from gas-burning equipment to the outdoors. Incorrect venting can create serious safety problems and should be checked carefully.
W
Water Heater
Equipment that heats water for fixtures, appliances, and some commercial uses. Water heaters may be gas, electric, tank, or tankless, and service depends on age, fuel type, location, condition, and access.
Wax Ring
A seal between the toilet and the drain connection at the floor. If the toilet is loose, the flange is damaged, or the ring fails, water can leak at the toilet base.
Z
Zoning
A system that uses dampers and controls to send conditioned air to specific areas or zones instead of treating the whole building the same way.
Call CTS Air Conditioning
CTS handles AC repair, HVAC service, replacement, maintenance, water heaters, and other plumbing across the Phoenix area.
480-696-5033