Air Duct & HVAC Dictionary

A removable or openable panel that allows a technician to reach an otherwise enclosed component or duct interior. Its location, construction, and closure method should suit the system. An access panel is different from a room register. When reviewing a cleaning quote, ask whether creating and closing access openings is included.

Annual Fuel Utilization Efficiency, a seasonal efficiency measure commonly used for fuel-burning furnaces and boilers. It compares useful heat output with fuel energy input under the rating method. It does not represent every loss between equipment and occupied rooms. Compare AFUE within its intended equipment category rather than treating it as interchangeable with heat-pump efficiency ratings.

The process of measuring and adjusting airflow so that an air distribution system more closely follows its intended design. It may involve measurements at outlets and adjustments to balancing devices. Balancing is different from simply turning every register fully open. Persistent room-temperature differences can require an assessment before adjustments are selected.

The volume of air supplied, removed, or exchanged in an hour divided by the space's volume, under a stated definition and measurement method. Often abbreviated ACH, it can describe different ventilation or testing contexts. A value from a building leakage test is not the same as the actual ventilation rate during ordinary occupancy.

Equipment that removes heat from a space and transfers it elsewhere, usually outdoors in a residential cooling system. It does not create cold as a separate substance. Cooling may also remove moisture when operating conditions permit. The equipment, controls, distribution system, and building all influence the comfort occupants experience.

The movement and delivery of conditioned or ventilation air through a building. It includes the routes, outlets, and return paths that connect equipment with occupied spaces. Equipment capacity alone does not describe distribution quality. A system can produce conditioned air while a particular room still has an airflow or building-related concern.

A passage that carries air as part of a heating, cooling, or ventilation system. Ducts may be made from different materials and can serve supply, return, or exhaust functions. The word does not identify the condition or service needed. Duct cleaning and repair address different kinds of findings.

The removal of particles from an airstream using a filter or other suitable filtration device. Performance depends on the filter, airflow, fit, and operating conditions. Filtration is different from bringing outdoor air indoors, and particle filtration does not automatically remove gases. A filter choice should be compatible with the equipment and its intended application.

An assembly that moves air and may contain a blower, filter, heating or cooling coils, and other components. Its configuration depends on the system. An air handler is not necessarily a fuel-burning furnace, even when the cabinets look similar. Identifying the actual equipment helps define an inspection, maintenance, or replacement proposal.

Work that reduces unwanted air leakage through gaps in the building enclosure. It is different from duct sealing and from adding insulation. The locations and methods should suit the building while accounting for ventilation and equipment needs. See insulation versus air sealing for questions that help distinguish these scopes in an estimate.

A heat pump that exchanges heat with outdoor air. Many residential models provide both heating and cooling by changing how the refrigeration system operates. Performance depends on equipment and conditions. The term identifies a system type, not a guarantee that every model has the same cold-weather capability or installation requirements.

The movement of air through a space, opening, or system. In HVAC discussions, airflow often refers to a volume moving per unit of time, such as cubic feet per minute. That is different from air speed at one point. A useful measurement identifies its location, operating conditions, and measurement method.

A condition that makes it harder for air to move through a particular part of a system. A loaded filter, obstructed opening, damaged duct, or other condition may contribute. The phrase describes an effect rather than a complete diagnosis. Finding the location and cause matters before choosing cleaning, repair, or equipment work.

Supplemental heating that supports a primary heating system under conditions determined by the equipment and controls. It is commonly discussed with heat pumps, although the particular heat source varies. An auxiliary-heat indication does not automatically establish a failure. Ask how the system is designed to operate before comparing normal staging with a diagnosed problem.

The fan assembly that moves air through equipment and the connected distribution system. Its operation interacts with filters, coils, ducts, and controls. A blower may run at one speed, several stages, or variable speeds depending on the equipment. A running blower alone does not prove that heating or cooling is operating correctly.

Heating equipment that transfers heat to water, or produces steam in a steam system, for distribution to heating devices. It differs from a furnace, which heats air for an air distribution system. The type of boiler and connected components matter when discussing service. A home can also have separate equipment for space cooling.

A fitting that connects a duct branch to a register or grille opening, often at a floor, wall, or ceiling. Its shape adapts the duct to the outlet location. A boot is part of the distribution path; the visible cover is a separate component. A loose cover does not establish the condition behind it.

A smaller duct path that leaves a larger distribution duct to serve an outlet or area. A system can have many branches with different lengths and fittings. Counting visible registers gives some information about the layout, but it does not fully describe branch routing, access, or the scope of a cleaning project.

British thermal unit, a unit of heat energy. Equipment capacity is commonly expressed in Btu per hour, which is a rate rather than a total quantity of heat. Distinguishing Btu from Btu/h makes product information easier to read. Neither value alone explains how well a particular room will be served by an installed system.

The parts of a building that separate the interior from outdoors or other surrounding conditions, including walls, roofs, floors, windows, and doors. People also use building enclosure for this concept. Its thermal and air-control characteristics interact with HVAC performance. A comfort complaint can involve the envelope as well as equipment and duct distribution.

The rate at which equipment can deliver heating or remove heat under specified conditions. It is different from efficiency, which relates useful output to energy input. More capacity is not automatically a better match. Installation estimates should explain how the proposed equipment was selected for the building and intended use.

Cooling provided by equipment serving multiple spaces through a distribution system, commonly ducts in a home. The equipment may be split between indoor and outdoor units or arranged as a package. Central describes the system arrangement, not a particular efficiency rating. Comfort still depends on sizing, installation, airflow, controls, and building conditions.

Cubic feet per minute, a unit of volumetric airflow. It describes how much air passes a point over time, rather than the temperature of that air or the equipment's heating capacity. When comparing measurements, ask where they were taken. A fan rating and a measured room-outlet airflow describe different parts of the system.

A heat-transfer component made from tubing and associated surfaces through which a fluid or refrigerant passes. Air moving across a coil exchanges heat with it. Coils serve different roles in different equipment. Calling a component the indoor coil identifies its location, while calling it an evaporator or condenser identifies its operating function.

A process of checking and documenting that installed systems operate according to defined project requirements. Its scope varies with the project and should be described in the agreement. The word does not guarantee that every possible performance test is included. Ask which checks, records, adjustments, and handoff information are part of the actual installation.

A component that raises refrigerant vapor pressure and circulates refrigerant through a refrigeration system. It is different from the fan that moves air across a coil. A compressor is one part of the overall cooling or heat-pump cycle. An outdoor unit that makes noise or has a spinning fan still requires proper diagnosis if performance changes.

Liquid water formed when water vapor condenses, such as on a cooling coil under appropriate conditions. HVAC systems use drainage arrangements to manage it. Condensate is different from refrigerant, even though both may be discussed near cooling equipment. Unexpected water should be traced to its source rather than automatically described as a refrigerant leak.

The drainage path that carries collected condensate away from equipment to an appropriate destination. Its arrangement depends on the installation and may include a trap, pump, or other components. A drain issue and a refrigerant issue are different service concerns. Describe the location of visible water when requesting an HVAC assessment.

A pump used in some installations to move collected condensate where gravity drainage alone is not suitable. It generally works with a reservoir and controls. Not every system needs one. When a pump is included in an installation estimate, ask how it fits the proposed drainage arrangement and what maintenance instructions apply.

The change from water vapor to liquid water when conditions allow it, often when humid air contacts a sufficiently cool surface. It can occur on equipment or building materials. Visible moisture does not identify its cause by appearance alone. A condensation concern should be distinguished from a plumbing leak, roof leak, or other source of water.

A heat exchanger where refrigerant releases heat and changes from vapor toward liquid during the refrigeration cycle. In a conventional cooling-mode split system, this function occurs outdoors. Heat-pump coil functions can change with operating mode. The outdoor cabinet is often called the condenser informally, but it contains more than the coil alone.

Coefficient of performance, the ratio of useful heating or cooling output to the energy input when both are expressed in consistent units. It describes performance under specified conditions. A single COP value is not a prediction of annual household bills. Equipment mode, temperatures, and the rating or measurement method provide essential context for comparison.

A device that regulates, directs, or stops airflow in a duct or opening. Dampers serve different purposes, including balancing, zoning, and specialized safety functions. They are not all operated in the same way. A service discussion should identify the damper type and role before treating its position as something to adjust casually.

Removal of moisture from air. Cooling equipment can provide some dehumidification, and dedicated dehumidifiers are designed specifically for that function. Reducing air temperature and controlling humidity are related but different tasks. A humidity complaint should be described with timing, location, and measurements when available, rather than assuming a lower thermostat setting will resolve it.

A difference between two temperatures, often written as ΔT. In HVAC service, it may describe the difference between air entering and leaving equipment or another pair of measurement points. Its meaning depends on those locations and operating conditions. A temperature difference is one piece of an assessment, not a universal pass-or-fail diagnosis by itself.

The temperature to which air would need to be cooled, at a given pressure and moisture content, for saturation and condensation to begin. It differs from relative humidity, which depends on the current air temperature. Dew point helps explain why a cool surface may collect water even when the surrounding air does not feel especially damp.

A rigid board material used to construct certain air ducts, commonly incorporating fiberglass and a facing. It differs from bare sheet-metal ductwork and flexible duct. The material and condition matter when selecting appropriate work. A service method suitable for one duct construction should not automatically be assumed suitable for every other construction.

Removal of accumulated material from the duct-system areas included in an agreed scope. The term alone does not specify every branch, return, or equipment component covered. Cleaning does not repair a disconnected duct or guarantee a health outcome. The cleaning estimate checklist helps make the proposed work understandable.

Air passing through openings or imperfect connections in a duct system instead of following only the intended path. Leakage location matters: supply and return leaks can have different effects. A visible gap may prompt assessment, while measuring leakage requires an appropriate test. Leakage is not the same thing as debris inside the duct.

Material installed on the inside surface of certain ducts, often for thermal or acoustic purposes. It is distinct from insulation wrapped around a duct's exterior. Its presence and condition can affect service decisions. Ask a provider to identify the material and explain a proposed cleaning or repair method before assuming all interiors are bare metal.

Work intended to reduce unwanted leakage through duct joints, connections, or other openings using suitable materials and methods. It differs from duct cleaning and from insulating the outside of a duct. A proposal should identify the areas being addressed and explain access limits. Sealing a duct does not by itself redesign its airflow path.

A system connecting outdoor equipment with one or more indoor units without using conventional large central ducts for those served spaces. Some mini-split systems use compact ducted indoor units, so terminology can overlap. Ductless does not mean maintenance-free or automatically suitable for every layout. Equipment selection and placement still require a project-specific design.

Energy Efficiency Ratio 2, a cooling-efficiency rating determined under a specified test procedure and operating conditions. It differs from SEER2, which represents seasonal cooling performance under its rating method. Compare ratings of the same kind. A numerical difference between EER2 and SEER2 does not mean one label is an error or a direct bill estimate.

A duct fitting that changes the direction of airflow. Its angle, shape, and relationship to nearby fittings influence the route and airflow resistance. The presence of elbows is normal and does not by itself indicate a defect. When layout changes are proposed, the complete path matters more than counting bends in isolation.

Heating produced as electric current passes through a resistive element. It appears in equipment such as electric furnaces and some heat-pump auxiliary heaters. It operates differently from a heat pump moving heat between locations. An equipment proposal should distinguish the primary heating method from any supplemental or backup heating arrangement.

Ventilation equipment, often abbreviated ERV, that exchanges heat and some moisture between outgoing and incoming air streams. It helps moderate the effect of outdoor-air ventilation on indoor conditions. It does not eliminate the need for heating or cooling equipment, and its suitability depends on the building, climate, system design, and operating requirements.

A heat exchanger where refrigerant absorbs heat as it evaporates. During cooling in a typical split air conditioner, the indoor coil serves this role. In a heat pump, the role can change with operating mode. The word describes a refrigeration function; it does not by itself identify whether the coil is clean or functioning properly.

Air removed from a building or space and discharged outside through an intended exhaust system. Bathroom fans and dryer exhaust are familiar examples with different applications. Exhaust air is not the same as return air circulated back to HVAC equipment. The proper arrangement depends on the appliance, purpose, and applicable installation requirements.

Air passing around a filter rather than through its intended filtering material. Gaps, poor fit, or an unsuitable housing can contribute. A higher-rated filter cannot perform its intended function on air that bypasses it. When discussing filtration, ask about the complete filter arrangement, including fit and compatibility, rather than comparing rating numbers alone.

Duct with a bendable construction, often including an inner liner, supporting wire, insulation, and an outer jacket. Its installed shape and support affect how it performs. Flexibility does not mean it can be routed without design considerations. Discuss visible compression, damage, or routing concerns through a duct repair assessment.

An informal term usually referring to outdoor air introduced into a building. Outdoor air is not automatically free of particles or gases, and return air is not equivalent to outdoor air. A ventilation proposal should explain the source, treatment, and intended flow of the air instead of relying only on the reassuring phrase fresh air.

Equipment that heats air for delivery through an air distribution system. Depending on the design, the heat source may involve fuel combustion or electric resistance. A furnace differs from a boiler that distributes heat through water or steam. Ask a replacement proposal to identify the equipment and the installation work, not only a brand name.

A cover with openings that allows air to enter or leave a space. Grilles are frequently used at return openings, although the term can describe other applications. A register generally includes an airflow-adjustment device, while a grille may not. Everyday usage varies, so photographs and location descriptions can help clarify which component is being discussed.

A component that transfers heat between substances or air streams while generally keeping them physically separated. The term applies to several HVAC components, including furnace and ventilation equipment. Its function and assessment depend on the specific system. A report mentioning a heat exchanger should identify the component and explain the finding rather than using the term alone.

Equipment that moves heat from one location to another using a refrigeration process. Many systems can provide space heating and cooling. Heat pumps are available in different configurations, including air-source and ground-source systems. A general description does not establish the right equipment for a property; capacity, controls, distribution, and installation must be considered together.

Ventilation equipment, often abbreviated HRV, that transfers heat between outgoing and incoming air streams to reduce the heating or cooling impact of ventilation. Its main distinction from an ERV concerns moisture transfer. Neither name specifies the entire installation. Ask how the unit, airflow, controls, and distribution will fit the particular building.

High-efficiency particulate air, a filtration designation. EPA lists HEPA performance as at least 99.97% capture at a particle size of 0.3 micrometers. A device described as HEPA still needs to be evaluated as a complete product, including airflow and intended use. It is not a synonym for every high-rated furnace filter. Compatibility and purpose matter when comparing room cleaners and central-system filtration.

Heating Seasonal Performance Factor 2, a seasonal heating-efficiency metric for heat pumps under a defined test method. It is different from a cooling-efficiency rating and from a furnace's AFUE. The number helps compare appropriately rated products, but actual energy use also depends on the building, weather, controls, installation, and household operation.

The addition of moisture to air using an appropriate device or system. It may be discussed when indoor air is dry, but the desired conditions depend on the building and circumstances. More moisture is not always better. Equipment settings and installation should account for the potential for condensation on cold surfaces and other building conditions.

A control that responds to humidity, similar in concept to a thermostat responding to temperature. It may control a humidifier, dehumidifier, or related equipment. A humidistat setting is not necessarily a precise description of conditions in every room. Sensor location, calibration, airflow, and the connected equipment influence how the system responds.

Heating, ventilation, and air conditioning: the combined field of controlling building temperature and managing air movement and related indoor conditions. The abbreviation can refer to equipment, systems, or the trade. It covers more than a furnace or air conditioner alone. Ask a proposal to identify the actual systems and tasks included under that broad label.

Space heating that uses circulating water to carry heat to devices such as radiators, baseboards, or radiant-floor tubing. It is different from forced-air heating through ducts. A hydronic system can have pumps, valves, and multiple zones. Describing those components accurately helps keep boiler work separate from unrelated air-conditioning or duct-cleaning services.

The condition of air within occupied buildings in relation to contaminants and other relevant factors. Often abbreviated IAQ, it is broader than whether ducts look clean or a room smells fresh. Source control, ventilation, filtration, moisture, and building conditions may all be relevant. No single service should be assumed to resolve every indoor-air concern.

Uncontrolled entry of outdoor air through openings and leaks in the building enclosure. It differs from intentionally supplied ventilation air. Weather and pressure differences can influence it. Infiltration may affect comfort and energy use, but a draft at one location does not quantify the entire building's leakage or establish the complete improvement needed.

Material used to slow heat flow through an assembly or component. It can be installed in building cavities or around certain ducts and pipes. Insulation is not the same as an air barrier, although some products can serve more than one function when appropriately installed. Installation scope should identify material, coverage, preparation, and relevant conditions.

Heat associated with a change of state, such as water vapor condensing to liquid, without the same kind of temperature change associated with sensible heating or cooling. In comfort cooling, moisture removal contributes to latent load. This distinction helps explain why managing temperature alone does not fully describe a system's handling of humid air.

The refrigerant piping that connects components of many split systems. It is distinct from air ducts, condensate drains, and electrical wiring. The required piping configuration depends on the equipment and installation. When reviewing a replacement quote, ask whether existing piping will remain and how its suitability for the proposed system will be assessed.

An assessment of the heating or cooling requirement of a building or space using relevant design information. It considers more than floor area alone. Load and equipment capacity are related but different concepts. When discussing repair versus replacement, ask how the proposed system selection accounts for the property and any planned changes.

A larger duct that carries air to or from several branches within a distribution system. It is often called a trunk duct. Its size and route are part of the overall design. A cleaning quote based only on individual room openings should still explain whether and how the relevant main ducts are included.

Air intentionally provided to replace air removed by an exhaust process. Its need and arrangement depend on the building and exhaust system. It is different from simply assuming leakage through the building will supply enough replacement air. An assessment should consider the relevant equipment, pressure relationships, and applicable project requirements before selecting an arrangement.

A sealant used in appropriate duct-sealing applications to close joints and openings. Product suitability, preparation, application, and system conditions matter. Mastic is not a generic name for every tape or coating, and a sealant should not be treated as structural support for damaged ductwork. Ask what a sealing proposal will actually address.

Minimum Efficiency Reporting Value, a rating used to describe a filter's particle-capture performance under a defined test. Higher ratings indicate greater capture efficiency for specified particle ranges, but the rating does not describe every feature of a filter. Follow equipment compatibility guidance; choosing a rating without considering airflow and fit can miss important system requirements.

An opening or connection through which a ventilation or air-handling system takes in outdoor air. It differs from a return grille drawing air from inside the building. Intake location, protection, treatment, and control depend on the design. Identifying the intake is useful when clarifying what a ventilation assessment or cleaning scope actually includes.

Equipment that combines major heating or cooling components within one cabinet rather than separating them into conventional indoor and outdoor units. Packaged equipment may serve residential or commercial applications. The cabinet's location does not explain the whole distribution system. Ask a service report to identify the unit, connected areas, and specific components involved.

An air compartment or chamber connected to ductwork, commonly near an air-handling unit or furnace. A supply plenum distributes outgoing air, while a return plenum collects incoming air. Building cavities may also be called plenums in certain arrangements. The exact configuration should be identified before discussing cleaning, access, or modifications.

A measure of resistance to heat flow through a material or assembly under defined conditions. A higher R-value indicates greater thermal resistance in that comparison. It does not by itself describe air leakage, installation quality, or every feature of an entire building. Ask an insulation estimate to identify both the material and the intended installed coverage.

A working fluid that absorbs and releases heat as it circulates through a refrigeration system. Different equipment uses different refrigerants, with specific handling and compatibility requirements. Refrigerant is not an air filter treatment or a substance that should be casually topped off as routine maintenance. A suspected refrigerant problem requires an appropriate equipment assessment.

A room air outlet or inlet cover that typically includes a device for adjusting airflow direction or quantity. People often use the word loosely for any vent cover. Adjusting registers is not equivalent to a professional airflow assessment. If one room remains uncomfortable, record the temperature pattern before assuming an outlet adjustment is sufficient.

The amount of water vapor in air compared with the amount associated with saturation at the same temperature, expressed as a percentage. Because temperature affects the comparison, relative humidity can change without adding or removing moisture. Record both temperature and humidity when describing a comfort concern so measurements have useful context.

Air drawn from occupied spaces back toward the heating or cooling equipment. It typically passes through a return path before being conditioned and supplied again. Return air is not automatically fresh outdoor air. Understanding the difference helps clarify whether a proposal concerns recirculation, filtration, outdoor-air ventilation, or several of those functions.

A valve used in many heat pumps to change the refrigerant flow arrangement between heating and cooling operation. It helps the system change which coil absorbs heat and which releases it. A mode-change problem is not automatically a reversing-valve failure; controls, electrical conditions, and other equipment findings must be evaluated before selecting a repair.

HVAC equipment installed on a roof, commonly encountered in commercial buildings. The name describes location and often refers to a packaged unit. Service planning must account for building access and the actual equipment configuration. For a business inquiry, identify access and approval contacts before the appointment rather than assuming roof access is available.

Seasonal Energy Efficiency Ratio 2, a seasonal cooling-efficiency rating based on a specified test procedure. It is used to compare qualifying equipment under that method. The older SEER label uses a different procedure, so the numbers should not be treated as automatically equivalent. A rating is not a guaranteed percentage reduction in your utility bill.

Heat transfer associated with a temperature change rather than a change of state. Warming room air or reducing its temperature involves sensible heating or cooling. It differs from the latent load associated with moisture removal. A system's total cooling capacity can include both components, so temperature readings alone do not describe its complete performance.

The target value a control is intended to maintain, such as the temperature selected on a thermostat. A setpoint differs from the actual measured condition and from conditions in other rooms. The system's controls determine how it responds around that target. A selected temperature alone does not prove that every part of the building has reached it.

Duct constructed from metal sheet formed into round, rectangular, or other shapes. Connections and fittings complete the airflow path. Some metal ducts have internal lining or external insulation, so the exterior appearance does not explain every layer. A service proposal should account for the actual construction, accessible areas, and observed condition.

Repeated operation in unusually brief on-and-off periods compared with the expected behavior of the particular system. Possible causes vary, so the phrase is a symptom description rather than a diagnosis. Record when it occurs and what equipment is involved. Do not assume equipment size, a thermostat, or one component is responsible without an assessment.

A heating or cooling arrangement with major components installed in separate locations, commonly an indoor unit and an outdoor unit connected by refrigerant piping. Split systems can be ducted or use other distribution arrangements. A replacement estimate should explain which components are being changed and how the proposed indoor and outdoor equipment work together.

Pressure in an air system considered separately from the component associated with air velocity. Technicians use pressure measurements to help evaluate system resistance and operation. Readings require defined locations and operating conditions. A number without those details is difficult to interpret, and a high or low reading does not identify a single cause by itself.

Air delivered by a system to a room or zone. Depending on the system, it may be heated, cooled, filtered, mixed with outdoor air, or otherwise treated. Supply air and return air describe different directions in the distribution path. An outlet's temperature alone does not establish the total airflow or heating and cooling capacity delivered.

A fitting that connects a branch duct to a larger duct or plenum. It creates the opening and connection through which that branch receives or returns air. The term is common in installation discussions. If a takeoff needs attention, ask the estimate to identify its location and whether the work concerns sealing, support, or replacement.

A temperature-responsive control used to request heating, cooling, or related system operation. Features vary from simple controls to connected, programmable devices. A thermostat's compatibility and settings must suit the equipment. Replacing the control is not automatically a solution for every comfort complaint, especially when airflow, equipment condition, or building factors are involved.

A unit of cooling capacity equal to 12,000 Btu per hour. It describes a rate of heat removal, not the equipment's physical weight. A three-ton rating therefore refers to nominal cooling capacity rather than three tons of machinery. Actual performance depends on conditions, and selecting capacity requires more than choosing the largest available unit.

A fitting that connects duct sections of different sizes or shapes. It allows the distribution path to change geometry without treating the entire run as one uniform size. A transition is distinct from an elbow, though fittings can combine functions. The design should account for the complete system rather than appearance alone.

Internal surfaces used in certain duct elbows to guide airflow through a change in direction. They are not present or required in every fitting. Their suitability depends on the duct design and application. Seeing a bend without vanes is not enough to diagnose an installation problem from a photograph or general checklist.

A material or layer that limits water-vapor diffusion through a building assembly. It is different from an air barrier, which addresses airflow, although a material can sometimes serve both roles. Placement and properties depend on the assembly and conditions. A general glossary definition is not a specification for adding a layer to an attic or wall.

Equipment capable of changing the speed of a motor or compressor over a range, depending on its design and controls. The phrase may refer to different components, so ask which one is variable-speed. It is not identical to every two-stage system. Evaluate the complete equipment and installation proposal rather than relying on the label alone.

The speed and direction of moving air, often discussed as feet per minute in HVAC work. Velocity differs from volumetric airflow: the same volume can travel at different speeds through different opening sizes. A measurement should state the location and method. Feeling a strong breeze at a grille does not quantify the entire system's airflow.

The intentional provision or removal of air to serve occupied spaces or a particular application. It may involve mechanical equipment, natural openings, or a designed combination. Ventilation differs from recirculating indoor air through a filter. Ask a proposal to explain the air source, route, controls, and intended purpose rather than treating every fan as equivalent.

Dividing a building's heating or cooling control into areas that can respond to different requirements. Zoning can use different equipment arrangements, controls, and distribution components. It does not necessarily mean each room has an independent system. A zoning proposal should explain how the areas, equipment, airflow, and controls are intended to work together.