Heating and Cooling Systems Vocabulary

Absolute pressure

Pressure measured from a perfect vacuum (zero); in psi it equals gauge pressure plus 14.7 at sea level.

Similar definitions: psia

Example: "A gauge reading of 35 psig equals 49.7 psi of         ."

Accumulator

A storage tank in the suction line just before the compressor that traps liquid refrigerant so only vapor reaches the compressor.

Similar definitions: suction accumulator

Example: "The          protects the heat pump compressor from liquid slugging during defrost."

Active listening

Fully concentrating on, understanding, and responding to a speaker.

Similar definitions: attentive listening

Example: "         helps the technician understand the customer's complaint."

AFUE (Annual Fuel Utilization Efficiency)

A rating of how efficiently a furnace or boiler converts fuel to heat over a typical year; 90% means 90% of the fuel energy becomes usable heat.

Similar definitions: seasonal heating efficiency

Example: "A condensing furnace with a 96%          wastes only 4% of its fuel energy."

Air handler

A central indoor unit containing the blower, heating or cooling coils, filter rack, and dampers that conditions and moves air through the ductwork.

Similar definitions: air handling unit, AHU

Example: "The heat pump's          sits in the attic with the evaporator coil and blower inside."

Air separator

A hydronic device that removes entrained air bubbles from circulating water so they can be vented from the system.

Similar definitions: air eliminator

Example: "Gurgling in the baseboard stopped after an          was installed near the boiler outlet."

Air-source heat pump

A heat pump that moves heat between outdoor air and the building, heating in winter and cooling in summer.

Similar definitions: air-to-air heat pump

Example: "An          loses heating capacity as the outdoor temperature drops, so backup electric heat is often added."

Americans with Disabilities Act (ADA)

A federal law that prohibits discrimination against people with disabilities in employment and public access.

Similar definitions: ADA

Example: "The          requires reasonable accommodations for qualified workers."

Ammeter

A meter that measures electric current in amperes; a clamp-on type measures current without breaking the circuit.

Similar definitions: clamp meter, amp clamp

Example: "The technician used a clamp-on          to check the compressor's running amperage."

Ampere

The unit of electric current, the rate at which electrons flow through a circuit.

Similar definitions: amp

Example: "The blower motor nameplate lists a full-load current of 4.2          (amps)."

Appliance (EPA)

Under Section 608, any device containing and using a CFC, HCFC, or substitute refrigerant for household or commercial use, such as an air conditioner, refrigerator, chiller, or freezer.

Similar definitions: refrigerant-containing equipment

Example: "EPA considers each independent refrigerant circuit of a multi-circuit system a separate         ."

Appliance connector

A listed flexible gas line that connects an appliance to the fixed gas piping.

Similar definitions: flex connector

Example: "The          must not pass through walls, floors, or cabinets."

Apprenticeship

A structured training program combining paid on-the-job training with classroom instruction, leading to a recognized credential.

Similar definitions: registered apprenticeship

Example: "Many HVAC technicians start through a union or contractor         ."

Aquastat

A temperature-sensing control on a boiler that regulates water temperature and can act as a high limit.

Similar definitions: boiler temperature control

Example: "The          was set to shut the burner off when boiler water reached 180°F."

Architect's scale

A three-sided ruler used to measure building drawings in feet and inches at reduced scales such as 1/4" = 1'-0".

Similar definitions: scale ruler

Example: "Using the 1/4-inch side of the         , the mechanical room measured 12 feet wide."

Area

The amount of surface within a shape, measured in square units; for a rectangle, length times width.

Similar definitions: surface area

Example: "The          of a 12-by-15-foot room is 180 square feet."

ASHRAE Standard 34

The standard that classifies refrigerants by toxicity (A = lower, B = higher) and flammability (1 = no flame propagation to 3 = higher flammability).

Similar definitions: refrigerant safety classification

Example: "Under         , R-410A is classified A1: low toxicity and no flame propagation."

Asphyxiation

Suffocation from lack of oxygen; refrigerants are heavier than air and can displace oxygen in enclosed spaces.

Similar definitions: oxygen deprivation

Example: "A large refrigerant leak in a basement mechanical room can cause         ."

Azeotropic blend

A refrigerant blend that behaves like a single refrigerant, boiling and condensing at one temperature with no glide; these blends are numbered in the 500 series.

Similar definitions: azeotrope

Example: "R-502 is an         , so it does not fractionate when it leaks."

Backdraft

A dangerous reverse flow of flue gases into the living space instead of up the vent, often caused by negative house pressure or a blocked chimney.

Similar definitions: spillage, downdraft

Example: "A          at the water heater draft hood can fill a basement with carbon monoxide."

Backflow preventer

A valve assembly that stops boiler water from flowing back into the potable water supply.

Similar definitions: backflow device

Example: "Codes require a          on the boiler's cold water fill line."

Bait and switch

A deceptive sales practice of advertising a low-priced product to lure customers, then pushing them toward a more expensive one.

Similar definitions: deceptive advertising

Example: "Advertising a $49 tune-up and then claiming it is unavailable is         ."

Baseboard heater

A low-profile heating unit along the bottom of a wall that warms rooms by convection using hot water or electric resistance elements.

Similar definitions: baseboard convector, fin-tube baseboard

Example: "Hot water from the boiler flows through copper fin-tube in each         ."

Belt tension

The tightness of a drive belt, adjusted so the belt grips the pulleys without overloading the bearings.

Similar definitions: belt deflection

Example: "Correct          allows about 1 inch of deflection per foot of span."

Black iron pipe

Uncoated steel pipe, joined with threaded fittings, that is the traditional material for natural gas and propane piping.

Similar definitions: black steel pipe

Example: "The gas main was run in 1-inch          with a sediment trap at the furnace."

Blower

The fan in a furnace or air handler that moves air across the heat exchanger or coil and through the duct system.

Similar definitions: indoor fan, blower motor

Example: "A slipping belt caused the          to move too little air across the coil."

Boiler

A closed vessel that heats water or produces steam to carry heat through piping to radiators, baseboard, or radiant tubing.

Similar definitions: hot water heater (hydronic), steam generator

Example: "A cast-iron          supplies hot water to the baseboard loops in each zone."

Brazing

Joining metals with a filler metal that melts above 840°F, used for refrigerant copper lines; nitrogen is flowed through the tubing to prevent internal oxidation.

Similar definitions: hard soldering

Example: "While          the suction line, the technician purged dry nitrogen through the tubing."

British thermal unit (BTU)

The amount of heat needed to raise one pound of water one degree Fahrenheit; HVAC capacity is commonly rated in BTU per hour.

Similar definitions: BTU

Example: "A 60,000          per hour furnace can heat a large home in a cold climate."

Bubble test

Applying soap solution to joints and watching for bubbles to locate gas or refrigerant leaks.

Similar definitions: soap test

Example: "The installer did a          on every gas fitting."

Builder's level

An optical instrument used with a grade rod to establish level lines and measure elevation differences on a site.

Similar definitions: transit level

Example: "The crew used a          to set the concrete pad for the condensing unit."

Burner

The device where fuel and air mix and combust to produce the flame in a furnace, boiler, or water heater.

Similar definitions: gas burner, oil burner

Example: "Rust flakes on the          caused a yellow, lazy flame."

Cad cell

A cadmium sulfide light sensor that proves flame in an oil burner; its resistance drops when it sees light.

Similar definitions: flame detector

Example: "A dirty          caused the oil burner to lock out."

Capacitor

An electrical component that stores a charge; start and run capacitors give single-phase motors the phase shift needed to start and run efficiently.

Similar definitions: run capacitor, start capacitor

Example: "A bulging          kept the condenser fan motor from starting."

Capillary tube

A fixed metering device made of a long, small-diameter copper tube that drops refrigerant pressure before the evaporator; common in small appliances.

Similar definitions: cap tube

Example: "The window air conditioner uses a          instead of an expansion valve."

Carbon monoxide (CO)

A colorless, odorless, poisonous gas produced by incomplete combustion of fuel.

Similar definitions: CO

Example: "A cracked heat exchanger can allow          to enter the supply air."

Carbon monoxide detector

An alarm that senses dangerous levels of carbon monoxide in a building and warns occupants.

Similar definitions: CO alarm

Example: "Every home with a gas furnace should have a working          near the sleeping areas."

Cave-in

The collapse of soil or rock into an excavation, the most serious trenching hazard.

Similar definitions: trench collapse

Example: "Shoring and sloping protect workers from a         ."

Celsius

The metric temperature scale on which water freezes at 0° and boils at 100° at sea level.

Similar definitions: centigrade

Example: "To convert 20°          to Fahrenheit, multiply by 9/5 and add 32."

Central air conditioning

A system that cools the whole building from one location, typically using a split system with an outdoor condensing unit and an indoor coil connected to ductwork.

Similar definitions: central AC

Example: "The home's          uses a 3-ton condensing unit and an evaporator coil on top of the furnace."

Certification

A credential showing a person has passed a test or met standards in a skill area, such as EPA 608 or NATE.

Similar definitions: credential

Example: "EPA 608          is legally required to handle refrigerants."

CFC (chlorofluorocarbon)

A refrigerant compound of chlorine, fluorine, and carbon, such as R-12, with the highest ozone depletion potential; production ended in the U.S. in 1995.

Similar definitions: Class I substance

Example: "R-12 is a          and can no longer be manufactured in the United States."

CFM (cubic feet per minute)

A measure of airflow volume; residential cooling systems typically move about 400 per ton.

Similar definitions: airflow

Example: "A 3-ton system needs roughly 1,200          across the indoor coil."

Charging

Adding refrigerant to a system to bring it to the manufacturer's specified amount, by weight or by superheat/subcooling.

Similar definitions: recharging

Example: "Blends such as R-410A must be          as a liquid to avoid changing the mix."

Check valve

A valve that allows fluid to flow in only one direction, preventing backflow.

Similar definitions: non-return valve, flow check

Example: "A          in the heat pump line set lets refrigerant bypass the metering device in one mode."

Chiller

A machine that removes heat from water or another liquid using a refrigeration cycle; the chilled water then cools air in coils throughout a building.

Similar definitions: water chiller

Example: "The office tower's centrifugal          uses low-pressure refrigerant R-123."

Circuit breaker

An automatic switch that opens a circuit when current exceeds its rating, protecting wiring from overheating.

Similar definitions: breaker

Example: "The condenser's          tripped when the compressor locked up."

Circulator pump

A pump that moves water through a closed hydronic loop, overcoming friction in the piping rather than lifting water.

Similar definitions: circulator

Example: "When the zone thermostat calls for heat, the          starts moving water to the baseboard."

Class A fire

A fire involving ordinary combustibles such as wood, paper, cloth, and many plastics.

Similar definitions: ordinary combustibles fire

Example: "A pile of burning cardboard boxes is a          that can be put out with water."

Class B fire

A fire involving flammable liquids or gases such as gasoline, oil, propane, or solvents.

Similar definitions: flammable liquid fire

Example: "A propane torch fire at a leaking fitting is a         ."

Class C fire

A fire involving energized electrical equipment, which must be fought with a non-conductive extinguishing agent.

Similar definitions: electrical fire

Example: "Never use water on a          in a live electrical panel."

Class D fire

A fire involving combustible metals such as magnesium, titanium, or sodium.

Similar definitions: combustible metal fire

Example: "Burning magnesium shavings create a          requiring a special dry powder agent."

Class K fire

A fire involving cooking oils and fats in commercial kitchens.

Similar definitions: kitchen fire, grease fire

Example: "A deep-fat fryer blaze is a          that calls for a wet chemical extinguisher."

Clean Air Act

The federal law whose Title VI (Section 608) protects stratospheric ozone by regulating refrigerant handling, recovery, and venting.

Similar definitions: CAA

Example: "Knowingly venting refrigerant violates the          and can bring fines per day per violation."

Closed-loop system

A geothermal system that continuously recirculates water or antifreeze through sealed buried or submerged piping.

Similar definitions: closed ground loop

Example: "A          never mixes its antifreeze solution with groundwater."

Coefficient of performance (COP)

The ratio of useful heating or cooling delivered to the energy put in; a COP of 3 means three units of heat per unit of electricity.

Similar definitions: COP

Example: "A geothermal heat pump with a          of 4 delivers four times more heat than the electricity it uses."

Combustion

The rapid chemical reaction of fuel with oxygen that releases heat; complete combustion of natural gas produces carbon dioxide and water vapor.

Similar definitions: burning

Example: "Proper          requires the correct mix of fuel, air, and an ignition source."

Combustion air

The outdoor or indoor air supplied to a fuel-burning appliance so the fuel can burn completely.

Similar definitions: makeup air for combustion

Example: "A furnace in a tight closet needs vents to supply enough         ."

Combustion analyzer

An instrument that samples flue gas to measure oxygen, carbon monoxide, carbon dioxide, temperature, and efficiency.

Similar definitions: flue gas analyzer

Example: "The technician inserted the          probe into the vent to check for CO."

Competent person

Under OSHA, a person capable of identifying existing and predictable hazards and authorized to take prompt corrective measures to eliminate them.

Similar definitions: qualified supervisor

Example: "A          must inspect the trench daily before workers enter."

Compound gauge

The blue low-side gauge on a manifold set that reads both positive pressure in psig and vacuum in inches of mercury.

Similar definitions: low-side gauge

Example: "The          showed 118 psig on the suction line."

Compressor

The pump in a refrigeration system that compresses low-pressure refrigerant vapor into high-pressure, high-temperature vapor, driving the cycle.

Similar definitions: refrigerant pump

Example: "The          is often called the heart of the refrigeration system."

Condensate

Water removed from the air when it is cooled below its dew point on the evaporator coil, or water formed from flue gases in a condensing furnace.

Similar definitions: drain water

Example: "A clogged drain line caused          to overflow from the coil pan."

Condensate pump

A small pump that lifts and removes condensate water when it cannot drain by gravity.

Similar definitions: condensate lift pump

Example: "The basement furnace needs a          because the floor drain is higher than the unit."

Condenser

The heat exchanger in a refrigeration system where hot, high-pressure refrigerant vapor releases heat and changes to a liquid; the hot side of the system.

Similar definitions: condenser coil

Example: "Dirt on the outdoor          coil raises head pressure."

Condensing furnace

A high-efficiency furnace (about 90% AFUE or higher) with a secondary heat exchanger that captures heat by condensing water vapor out of the flue gases.

Similar definitions: high-efficiency furnace, 90+ furnace

Example: "A          vents through PVC pipe because its flue gases are cool and acidic."

Condensing unit

The outdoor section of a split system containing the compressor, condenser coil, and condenser fan.

Similar definitions: outdoor unit

Example: "The          was set on a level pad at least a foot from the house."

Conduction

Heat transfer through a solid or between objects in direct contact, from the warmer to the cooler material.

Similar definitions: thermal conduction

Example: "Heat moves by          through the copper wall of the tube into the refrigerant."

Confined space

A space large enough for a worker to enter, with limited means of entry or exit, and not designed for continuous occupancy.

Similar definitions: restricted space

Example: "A crawlspace beneath a home can be a          when installing ductwork."

Conflict of interest

A situation in which personal gain could improperly influence a person's professional decisions.

Similar definitions: competing interests

Example: "Accepting gifts from a supplier while choosing bids is a         ."

Conflict resolution

Methods for settling disagreements in a fair and productive way.

Similar definitions: dispute resolution

Example: "Using          skills, the technician calmly handled the upset customer."

Consumer protection laws

Federal and state laws that protect buyers from unfair, deceptive, or fraudulent business practices.

Similar definitions: consumer rights laws

Example: "Ohio's          require honest estimates for home repairs."

Contactor

A heavy-duty electrically operated switch that uses a low-voltage coil to close contacts carrying high-voltage power to the compressor and condenser fan.

Similar definitions: relay, magnetic starter

Example: "When the thermostat calls for cooling, 24 volts energizes the          coil."

Continuity

An unbroken, complete path for current, checked with an ohmmeter; an open circuit has no continuity.

Similar definitions: closed path

Example: "The technician checked the limit switch for          with the power off."

Convection

Heat transfer by the movement of a fluid such as air or water, where warmer, less dense fluid rises and cooler fluid sinks.

Similar definitions: natural convection, forced convection

Example: "Baseboard heaters warm a room mainly by         ."

CPR (cardiopulmonary resuscitation)

An emergency procedure of chest compressions, often with rescue breaths, used on someone whose heart or breathing has stopped.

Similar definitions: CPR

Example: "The coworker began          after the victim collapsed from an electrical shock."

CSST (corrugated stainless steel tubing)

Flexible, coated stainless steel gas piping that must be listed, installed per the manufacturer's instructions, and bonded to reduce lightning damage.

Similar definitions: flexible gas line

Example: "The new gas range was supplied with yellow-jacketed         ."

Cultural intelligence

The ability to understand and work effectively with people from different cultural backgrounds.

Similar definitions: cultural competence

Example: "         helps a crew with diverse members work well together."

Customer service

The assistance and courtesy a business provides to its customers before, during, and after service.

Similar definitions: client relations

Example: "Good          includes explaining repairs and cleaning up the work area."

Cut-in / cut-out

The pressure or temperature settings at which a control turns equipment on (cut-in) and off (cut-out).

Similar definitions: set points, differential

Example: "The low-pressure switch has a          of 50/25 psig."

Cyber hygiene

Routine practices, such as strong passwords and software updates, that protect devices and data from cyber threats.

Similar definitions: cybersecurity practices

Example: "Locking your tablet and using strong passwords are part of good         ."

Damper

A plate or louver in a duct that opens or closes to control airflow.

Similar definitions: volume damper, balancing damper

Example: "Closing the          in the bedroom duct reduced airflow to that room."

Deenergize

To disconnect a circuit or equipment from all power sources so it carries no voltage.

Similar definitions: de-energize, kill power

Example: "         the unit and test for voltage before replacing the capacitor."

Defrost cycle

A heat pump operation that temporarily reverses to cooling mode to melt frost from the outdoor coil.

Similar definitions: defrost mode

Example: "Steam rising from the outdoor unit in winter is normal during a         ."

Dehumidification

The removal of moisture from the air, as happens when air passes over an evaporator coil colder than its dew point.

Similar definitions: moisture removal

Example: "An air conditioner provides          along with cooling."

Delta T

The temperature difference between two points, such as supply and return air or entering and leaving water.

Similar definitions: temperature difference, temperature split, ΔT

Example: "A cooling          of about 20°F across the evaporator is typical."

Desuperheater

A small heat exchanger in a geothermal heat pump that uses hot refrigerant gas to preheat domestic hot water.

Similar definitions: hot water assist

Example: "In summer the          makes nearly free hot water from heat removed from the house."

Dew point

The temperature to which air must be cooled for its relative humidity to reach 100% and water vapor to begin condensing.

Similar definitions: saturation temperature of air

Example: "When the duct surface falls below the         , it begins to sweat."

Diffuser

A supply outlet with vanes that spreads conditioned air in several directions into a room.

Similar definitions: register, supply outlet

Example: "The ceiling          throws air in four directions."

Digital multimeter (DMM)

A meter that measures voltage, resistance, and current, and often capacitance and temperature.

Similar definitions: multimeter, VOM

Example: "The technician used a          to check for 240 volts at the disconnect."

Direct-vent appliance

A sealed-combustion appliance that takes all combustion air from outdoors and vents all flue gases outdoors through dedicated pipes.

Similar definitions: sealed combustion

Example: "A          cannot backdraft into the living space."

Disconnect switch

A switch located within sight of the outdoor unit that cuts power so the equipment can be safely serviced.

Similar definitions: service disconnect

Example: "Pull the          and verify zero voltage before touching the contactor."

Disposable cylinder

A single-use refrigerant container (DOT-39) that must never be refilled; it must be emptied to 0 psig before disposal.

Similar definitions: DOT-39 cylinder

Example: "A          of new R-410A must not be used to hold recovered refrigerant."

Draft

The pressure difference that moves flue gases up a chimney or vent and draws combustion air into the appliance.

Similar definitions: chimney draft, stack effect

Example: "A weak          can cause flue gases to spill at the draft hood."

Draft hood

A device on a natural-draft appliance that lets dilution air enter the vent and prevents downdrafts from affecting the burner.

Similar definitions: draft diverter

Example: "Spillage at the water heater's          indicates a venting problem."

Draft inducer

A motor-driven fan that pulls combustion gases through the heat exchanger and pushes them out the vent in a furnace.

Similar definitions: inducer motor, induced draft fan

Example: "The          starts first so the pressure switch can prove venting."

Dry bulb temperature

Air temperature measured by an ordinary thermometer shielded from radiation and moisture.

Similar definitions: air temperature

Example: "The room's          was 75°F while the wet bulb read 62°F."

Duct

A metal or flexible passage that carries supply or return air between the equipment and the rooms.

Similar definitions: ductwork

Example: "Leaky          joints in the attic waste a great deal of cooling."

EER (energy efficiency ratio)

An air conditioner's cooling output in BTU per hour divided by its power input in watts at one specific outdoor condition.

Similar definitions: steady-state cooling efficiency

Example: "Unlike SEER,          is measured at a single 95°F outdoor temperature."

Electric furnace

A forced-air furnace that heats air by passing it over electric resistance heating elements controlled by sequencers.

Similar definitions: electric resistance furnace

Example: "An          has no flue because nothing is burned."