HVAC system types: a field guide to choosing a system

What are the main types of HVAC systems?

An HVAC system is the equipment that heats, cools, and ventilates a building, and the type is named by a handful of choices that stack together rather than by one label. The first choice is how the system makes heating and cooling. The second is how it distributes that to the space, by air, by water, or by refrigerant. The third is whether the equipment is packaged into one cabinet or split across indoor and outdoor pieces. The fourth is whether one central plant serves the building or a unit sits at each zone. The last is the fuel or the source: gas, electricity, or heat moved from the air, water, or ground.

Read those axes and almost every system name falls into place. A residential split system is refrigerant-distributed, split, decentralized, and usually gas or electric heat with electric cooling. A chilled-water plant is water-distributed, central, and serves a high-rise from one room. VRF is refrigerant-distributed, decentralized, and zoned. The label on the cut sheet is shorthand for where the system lands on each axis.

This guide maps the families and points to the deep ones. The water-versus-refrigerant decision on a commercial building, and the size where a central plant beats distributed cooling, is worked through in the chilled water vs DX cooling comparison guide. How a heat pump heats and cools with one machine, and where it hands off to backup heat, is in the heat pump fundamentals guide. Use this overview to pick the family, then go deep on the one the building wants.

Air, water, or refrigerant: the distribution split

The most useful way to sort HVAC systems is by what carries the heat to the space, because that one decision sets the reach, the cost, and the feel of the system. There are three carriers: air, water, and refrigerant.

An all-air system conditions air at a central unit and ducts it to the rooms. The duct is the system, and the air does double duty, carrying both the temperature and the fresh-air ventilation. It is simple to follow and it handles filtration and ventilation in one path, but ducted air is bulky and loses reach over distance, so a single air handler serves only so far before the duct gets impractical.

An all-water, or hydronic, system pipes hot or chilled water to terminal units in the space, fan coils, radiation, or coils in local air handlers, and lets water do the heavy carrying. Water moves heat far more effectively than air or refrigerant lines, so a hydronic loop reaches across a campus or up a high-rise from one plant. The trade is that water needs pumps, treatment, and a plant, and a separate path still has to bring in ventilation air.

Refrigerant distribution, DX or VRF, runs refrigerant itself out to coils at or near the zone. It is compact and efficient over moderate distances, but the refrigerant line length is capped by the manufacturer, and the refrigerant ends up spread through the building. Which carrier fits is the first fork, and it is worked in depth for the commercial cooling case in the chilled water vs DX cooling comparison guide.

What is the difference between a packaged and a split system?

A packaged system holds the whole refrigeration circuit in one cabinet, while a split system divides it between an indoor unit and an outdoor unit joined by a refrigerant line set. That is the entire distinction, and it drives where the equipment sits and who does the field refrigerant work.

A packaged unit, the rooftop unit being the common one, arrives factory-charged and sealed. You set it, connect duct, power, and condensate, check rotation, and verify the factory charge. There is no field brazing and no field circuit to build. The unit has to live where it can serve the space, usually on the roof or on a slab, and the air is ducted from there.

A split system puts the compressor and condenser outside and the coil or air handler inside, with refrigerant piping run between them in the field. That buys flexibility, the noisy half goes outside and the coil goes where the air is, and it pays for it with jobsite refrigerant work: brazing the line set, pulling a deep vacuum, and setting the charge. Every field joint is a future leak someone signed for. Packaged is faster and more repeatable to commission. Split reaches places a single cabinet cannot.

Centralized vs decentralized (zoned) systems

Centralized means one plant makes the heating or cooling for the whole building and distributes it. Decentralized means a unit sits at or near each zone and makes its own. The split changes where the equipment lives, how the building fails, and how finely it zones.

A central system, a chilled-water plant or a big central air handler, concentrates the machinery in one mechanical room. It is efficient at scale and lasts decades, but if it has no spare capacity it can take the whole building down at once, which is why serious plants are built with redundancy. It also leans hard on the controls to distribute and reset correctly.

A decentralized system, packaged rooftop units, mini-splits, PTACs, or VRF, spreads many small units around the building. One failure takes one zone, not the building, and a tech services a single unit without touching the rest. The cost is many units to maintain, often in the weather, and a coarser or more piecemeal approach to ventilation. Most real buildings are a blend: a central plant for the bulk load and local units for the edges, or a decentralized scheme with a central ventilation system layered over it.

The residential split system: furnace or heat pump plus air handler

The split system is the system in most homes and a lot of small commercial space: an outdoor condensing unit, an indoor coil and air handler or furnace, refrigerant lines between them, and ducts to the rooms. It is refrigerant-distributed at the unit and air-distributed to the space, decentralized, and split.

Two flavors cover the field. A furnace plus AC pairs a gas or electric furnace for heat with a separate cooling coil and outdoor condenser, two heat sources in one cabinet stack. A heat pump replaces the AC with a unit that runs both directions and heats by moving heat instead of burning fuel, usually with electric strip or a furnace as backup. How the heat pump version works, COP, the balance point, defrost, and the dual-fuel handoff, is the subject of the heat pump fundamentals guide.

The split system owns the residential market because it is cheap to buy, fast to install, and easy to service, and because the ductwork it needs is already how houses move air. Its limit is the duct. A single air handler serves one main zone well and several zones poorly without added dampers or a second system, which is where mini-splits and zoning come in.

The packaged rooftop unit (RTU) for light commercial

The rooftop unit is the workhorse of light commercial: a single cabinet on the roof holding the compressor, condenser, evaporator coil, blower, often a gas heat section, and an economizer, ducted down into the space below. It is all-air distribution, packaged, and usually one unit per zone or tenant.

RTUs own strip malls, big-box stores, offices, and schools because they keep the mechanical equipment off the rentable floor, install fast on a curb, and let each tenant or zone run on its own. The unit is factory-charged and sealed, so startup is setting the curb, connecting duct and power, checking rotation and the economizer, and verifying the charge rather than building a circuit. RTU installation and startup is its own discipline, worth reading by topic.

The catch is the roof. A row of RTUs loads the structure, puts every filter, belt, and coil up in the weather, and turns the roof into a maintenance floor with curbs and penetrations to keep watertight. RTUs also tend to be single-zone per unit, so a building that needs fine zoning either adds units or moves to VAV off a larger air handler.

The ductless mini-split

A ductless mini-split is a split system with no ductwork: one outdoor condensing unit feeds one or a few indoor heads on the wall or ceiling, with refrigerant lines run to each head and no duct at all. It is refrigerant-distributed straight to the zone, decentralized, and split.

Mini-splits win where there is no duct and adding it is expensive or impossible: additions, retrofits of old buildings, converted spaces, server closets, and rooms a central system cannot reach or control. Each head is its own zone with its own setpoint, so a mini-split zones room by room without dampers. Most are heat pumps, so they heat and cool from the same equipment, and the cold-climate versions hold capacity well below freezing.

The trade is ventilation and looks. A mini-split recirculates and conditions room air but brings in no fresh air on its own, so ventilation has to come from somewhere else. The indoor heads are visible in the room, and a multi-head system still carries refrigerant to every head, with the line-length and refrigerant-charge limits that come with it.

What is a VRF system?

VRF, variable refrigerant flow, is split DX scaled up: one outdoor unit feeds many indoor units through a shared refrigerant network and varies the refrigerant flow to each head to match its load. VRV is the same technology under one manufacturer's trademark. A single outdoor unit can serve dozens of indoor units, each controlled to its own zone.

The feature that sets VRF apart is heat recovery. A heat-recovery VRF system cools some zones while heating others at the same time, moving heat from the rooms that have too much to the rooms that need it instead of rejecting it outside. In a building with a hot south face and a cold north face in the same hour, that is real energy saved.

VRF competes directly with chilled water on zone-heavy mid-size buildings, offices, hotels, and schools, that want individual room control without a central water plant. It is still DX, so it carries DX's constraints in sharper form: long refrigerant networks, a large total refrigerant charge in the building, and the line-length and refrigerant-safety limits that come with that. The VRF case against a central plant is worked through in the chilled water vs DX cooling comparison guide.

Furnace plus AC, heat pump, or dual-fuel

The heating side of a residential or light-commercial system comes down to three setups, and the choice is about fuel and climate as much as equipment. A furnace plus AC burns gas or runs electric resistance to make heat and uses a separate refrigerant circuit to cool. A heat pump moves heat both directions, heating in winter and cooling in summer from one system, with electric strip or a furnace as backup. A dual-fuel, or hybrid, system pairs a heat pump with a gas furnace and switches between them at an outdoor temperature.

The lean depends on what heat costs and how cold it gets. Where gas is cheap and winters are hard, a gas furnace delivers brute heat and very hot supply air, and dual-fuel lets the heat pump carry the mild hours while the furnace takes the deep cold. Where electricity is the cleaner or the only option, an all-electric heat pump with backup is the electrification answer, and cold-climate equipment has pushed it into regions that wrote it off a decade ago.

The mechanics, COP, the balance point, the defrost cycle, and where dual-fuel hands off, are covered in the heat pump fundamentals guide. The selection here is fuel, climate, and operating cost, not a fixed rule.

The chilled-water plant

A chilled-water plant is the central cooling system for large buildings: a chiller makes cold water, usually in the low 40s Fahrenheit, and pumps move it through the building to coils in air handlers, fan coils, and VAV systems. The refrigerant stays in the chiller and its room. What travels the building is water.

This is water distribution at full scale, and it owns high-rises, hospitals, campuses, and large offices because water carries heat far enough to serve a whole building from one mechanical room. The chiller can be air-cooled, rejecting heat straight to outdoor air, or water-cooled through a cooling tower, which is more efficient at scale and adds a tower, condenser-water pumps, and water treatment. Bringing a plant online and proving it makes its tons at the right efficiency is its own job, covered in chiller plant startup and commissioning by topic.

A chilled-water plant costs more to build than distributed cooling and earns it back through efficiency and a 25 to 30 year life on a building big enough to use it. The chilled water versus distributed DX decision, including where the size crossover sits, is the subject of the chilled water vs DX cooling comparison guide.

The boiler and hydronic heating

A boiler is the water-side equivalent for heating: it makes hot water or steam and pumps it through the building to radiation, baseboard, radiant floors, fan coils, or heating coils in air handlers. It is the heating half of a hydronic building, and it pairs naturally with a chilled-water plant on the cooling side.

Hydronic heat is quiet, comfortable, and reaches as far as the pipe runs, which is why it shows up in older buildings, multifamily, schools, and anywhere radiant or perimeter heat is wanted. A condensing boiler pulls extra efficiency out of the flue gas by running return water cool enough to condense it, so low return-water temperature is what keeps a condensing boiler in its efficient range. Run it with hot return water and the efficiency it was bought for never shows up.

The fuel question is live on the boiler too. Gas boilers are being weighed against air-to-water and ground-source heat pumps that make hot water without combustion, as the electrification push reaches the heating plant. Boiler sizing, piping, and controls are their own topic worth reading separately.

The central air handler and VAV system

The commercial all-air system is a central air handling unit feeding variable-air-volume boxes: one large AHU conditions air, filters it, brings in outside air, and pushes it down a main duct, and a VAV box at each zone throttles the airflow to hold that zone's temperature. Many VAV boxes add a reheat coil so a zone can warm its air when it needs less cooling than its neighbors.

This is how large offices and institutional buildings handle many zones from central equipment. The AHU does the heavy conditioning and ventilation in one place, and the VAV boxes do the zoning, so you get fine room-by-room control without a unit in every room. The cost is duct, a lot of it, and a controls system that has to stage the AHU, reset the supply-air temperature and duct static pressure, and keep the boxes and the fan at efficient points.

The classic energy waste in a VAV system is simultaneous heating and cooling: chilling the central air down, then reheating it at the box. Good supply-air-temperature reset and minimum-airflow setup are what hold that waste down. AHU and VAV setup and air balancing are their own disciplines worth reading by topic.

Fan-coil units and the four-pipe system

A fan-coil unit is a small terminal that blows room air across a water coil and delivers it back to the space, one unit per room or small zone, fed from a central plant. It is water distribution to a local unit, and it is the system behind most hotels, apartments, and hospitals, where every room wants its own control.

The piping arrangement is the thing to get right. A two-pipe system runs one supply and one return and can deliver either hot or chilled water to the whole building at once, but not both, so it cannot heat one room while cooling another and forces a seasonal changeover. A four-pipe system runs separate hot-water and chilled-water supply and return to each coil, so any room can heat or cool at any time. Four-pipe costs more in pipe and coils and buys year-round, room-by-room flexibility, which is why hotels and hospitals specify it.

Fan coils zone finely and keep the refrigerant in the central plant, but each unit has a filter, a fan, a coil, and a condensate pan in the occupied space. That means many small units to maintain and a condensate path to keep clear in every room.

Water-source and geothermal heat pumps

A water-source heat pump system puts a small heat pump in each zone, all tied to a common water loop instead of individual outdoor units. Each unit pulls heat from or rejects heat to the loop, so a zone that needs cooling dumps heat into the loop that a zone needing heat can pick up, which makes the loop a heat-sharing path across the building.

The loop is held in a comfortable range by a boiler and a cooling tower, or, in a geothermal system, by buried ground loops. Ground a few feet down sits at a stable temperature year round, far milder than winter air, so a ground-source loop lets every heat pump run a higher COP and hold capacity through cold snaps that pull an air-source unit down. The cost is the loop field, horizontal trench or vertical bore, which is the expense and the complexity an air-source unit avoids.

Water-source and geothermal systems suit buildings with a lot of simultaneous heating and cooling and owners who will invest first cost for low operating cost. The ground-source version of the cycle is touched on in the heat pump fundamentals guide, and the loop design and flushing are their own topic.

PTAC and PTHP: the through-wall terminal

A PTAC, packaged terminal air conditioner, is a self-contained unit that mounts through an exterior wall and conditions one room, the under-window unit in most hotel rooms and a lot of senior housing and apartments. The whole refrigeration circuit is in one chassis, so it is packaged, decentralized, and about as simple as HVAC gets. A PTHP, packaged terminal heat pump, is the same unit with a reversing valve, so it heats by moving heat instead of pure electric resistance.

PTACs win on first cost, independence, and replacement. A failed unit is swapped through the same wall sleeve in an afternoon without touching the rest of the building, and every room is its own zone billed to its own meter. That makes them a default for hospitality and multifamily where rooms turn over and simplicity matters.

The trade is efficiency, noise, and the wall penetration. A PTAC is not an efficient machine, it sits in the room making fan noise, and the sleeve is a hole in the envelope. The PTHP is the more efficient choice in moderate climates and is being pushed by electrification programs, with room heat pumps arriving to replace older PTAC stock.

DOAS plus zoning: decoupling ventilation from conditioning

A dedicated outdoor air system, DOAS, splits the job in two: one system conditions and delivers fresh outdoor air, and a separate set of terminals handles the heating and cooling of the space. Instead of one all-air system carrying both the ventilation and the temperature load in the same oversized airstream, the ventilation air gets its own right-sized path.

The reason to decouple is that the two loads do not track each other. A space needs a fixed amount of fresh air for the people in it, but its heating and cooling load swings with the weather and the sun. Size one airstream for both and you are always compromising one of them. A DOAS delivers the ventilation air, usually with energy recovery off the exhaust and often dried out so it carries the latent load, while fan coils, VRF heads, chilled beams, or VAV boxes handle the sensible heating and cooling per zone.

DOAS plus a zoned sensible system is a common modern pattern because it ventilates correctly without the reheat waste of an all-air system pushed to its low-load limit. Setting the DOAS supply conditions and the zone terminals to work together is where the design is won, and it is worth reading on DOAS and zoning by topic.

How do you choose an HVAC system?

Choose on the building first, then the load, the zoning the spaces need, the fuel and electrification goals, the efficiency target, the first-cost-versus-operating-cost balance, and the space and structure available for equipment. No single factor decides it. The honest selection runs a load calculation, looks at how the building zones, and compares first and life-cycle cost before it picks a family.

The pattern across most projects is size and zoning leading. Small buildings and homes lean on split systems and packaged units, because the first cost and the simplicity win. Mid-size, zone-heavy buildings lean on VRF, water-source heat pumps, or fan coils for room-by-room control without a giant plant. Large, tall, or long-running buildings lean on a central chilled-water and boiler plant with air handlers and VAV, because the efficiency and reach pay off at scale. A data center or a hospital adds redundancy that pushes toward a central plant built with spare capacity.

The matrix below is where to start, not a verdict. Weigh the factors against each other for the specific building, because the same square footage spread out one story leans a different way than stacked in a tower.

Heating source and electrification

The heating source is now a live design decision, not a default to gas. The three sources are combustion (a gas or oil furnace or boiler), electric resistance (strip heat, cheap to install and expensive to run), and a heat pump (which moves heat and delivers more than it draws). The decarbonization push is moving new and retrofit work off combustion and onto heat pumps wherever the climate and the budget allow.

The case for the all-electric building is that a heat pump running on a grid that keeps getting cleaner beats on-site combustion on emissions, and incentives and tightening energy codes are pushing the switch. Cold-climate air-source equipment, air-to-water heat pumps for hydronic buildings, and water-source and geothermal systems are the tools making it work in heating-dominated regions. Dual-fuel is the hedge: keep the gas furnace for the deep cold and let the heat pump carry the rest.

This is a fuel and policy question as much as an engineering one, and it varies by jurisdiction, utility rate, and incentive. Confirm the local electrification requirements and rebates, because some jurisdictions now restrict new gas service and others still favor gas on cost.

Efficiency metrics and code by system type

Each system family is rated by its own efficiency metric, and matching the right metric to the right equipment is half of comparing systems honestly. Residential and small unitary cooling carries SEER2 and EER2; heat-pump heating carries HSPF2. Commercial unitary equipment above 65,000 BTU per hour is rated on IEER, a part-load number, because a rooftop unit runs at full load only a small fraction of the time. Chillers are rated on kW per ton and the part-load IPLV. Furnaces and boilers carry AFUE, the season-long fuel-to-heat percentage.

The 2023 federal update added the '2' suffix to SEER and HSPF because the test method moved to a higher external static pressure that better matches real duct. A SEER2 number reads a little lower than the old SEER for the same equipment, so do not compare across the change and conclude the unit got worse.

ASHRAE Standard 90.1 sets the minimum efficiencies for commercial equipment, and the adopted energy code is what makes them enforceable. The floors tighten most cycles, so confirm the adopted edition and any state amendments. Treat efficiency comparisons between system types as design-dependent and worth confirming for the actual climate, load, and equipment rather than carrying a brochure number as a fixed fact.

Zoning and controls by system type

How finely a system zones is set by the system type, and it is one of the first questions a building should answer. A single packaged unit is one zone, or a few with zoning dampers, and adding zones means adding units, which is coarse but dead simple. A VAV system zones at every box off one air handler, giving fine control across a large building from central equipment. VRF, fan coils, water-source heat pumps, and mini-splits zone at every indoor unit, room by room.

The finer the zoning, the more the building rides on the controls being commissioned right. A central system, chilled water with VAV, leans hard on the control system to stage the plant, reset the water and air temperatures, and hold the equipment at its efficient points. Get those controls wrong and the system runs, but it runs expensive, and nobody notices for years.

Match the zoning to how the building is actually used. A warehouse wants one or two big zones. A hotel wants a zone per room. Putting a single-zone system where the spaces needed independent control, or a complex zoned system where one zone would have done, are both common and both expensive in their own direction.

Ventilation and indoor air quality by system type

Every system has to bring in fresh outdoor air, and how it does that varies by type, which is easy to overlook until the building fails a ventilation check or feels stuffy. An all-air system, a rooftop unit or a central AHU, handles ventilation in the same airstream that heats and cools, usually with an economizer and an outdoor-air damper, so ventilation comes built in.

The systems that condition recirculated room air bring in little or no fresh air on their own. A mini-split, a fan coil, a PTAC, or a VRF head conditions the air already in the room, so ventilation has to be added: a separate outdoor-air path, an energy-recovery ventilator, or a dedicated outdoor air system layered over the zone units. This is exactly the gap a DOAS fills, and it is why DOAS-plus-zoning has become the modern pattern.

ASHRAE Standard 62.1 sets the minimum outdoor-air rates for commercial spaces and 62.2 for dwellings, and the adopted mechanical code makes them enforceable. Pick a zone-conditioning system without planning the ventilation path and you have specified half a building. Ventilation and DOAS design are worth reading by topic.

Residential, commercial, and industrial system map

Which system fits which building is the question every other section feeds, and the map is steadier than any single rule. Residential and small commercial run on split systems, packaged units, mini-splits, and PTACs, because first cost and simplicity decide it. Mid-size commercial runs on rooftop units, VRF, water-source heat pumps, and fan coils, where zoning starts to matter and a plant is not yet justified. Large and institutional buildings run on central chilled-water and boiler plants with air handlers, VAV, and fan coils, where efficiency, reach, and redundancy pay off.

Industrial is its own world, where process loads, not human comfort, drive the system: makeup air units, process cooling, large hydronic loops, and equipment sized to a thermal process rather than an occupancy. A data center is the sharpest special case, a building whose cooling cannot go warm and whose load runs year round.

The table maps the common fit. Treat it as the starting frame, because a spread-out single-story building leans distributed longer than a tall, dense one of the same area, and the load calculation settles the call.

Data-center cooling as a special HVAC case

A data center is HVAC with the comfort removed and the stakes raised: the load is servers, it runs year round, and it cannot go warm without losing equipment. The same families show up under different names. A CRAC, computer room air conditioner, is a DX unit cooling the room directly. A CRAH, computer room air handler, runs room air over a chilled-water coil fed by a central plant. The DX-versus-chilled-water call is the same one a large building makes, and it is worked through in the chilled water vs DX cooling comparison guide.

What is different is density and the move to liquid. As racks pack more power into less space, blowing cold air at them stops keeping up, so high-density and AI compute halls are moving to liquid cooling: rear-door heat exchangers, direct-to-chip cold plates, and immersion, all of which bring water or coolant much closer to the chip than room air ever does.

The other special trait is heat recovery. A data center makes large waste heat all year, and recovering it to warm offices or a district loop turns a cooling cost into a heating source, which the heat pump fundamentals guide touches on. Redundancy is not optional here, so the plant is built with spare capacity from the start.

What to document

When you pick a system family for a building, put the decision on paper so it is defensible later, because the question of why this system and not another always comes back. Record the building type and size, the design load, the distribution carrier, the packaged-or-split and central-or-distributed choices, the heating source and fuel, the efficiency target and metric, and the zoning and ventilation approach. If the choice was close, write down what the alternative was and why it lost.

The table is the frame. Fill it with the building's real numbers, the load calculation, the routed distribution lengths, the local energy rates, and the efficiency the project is held to, not generic figures.

Common mistakes

• Picking the system on the building next door instead of running the load and the zoning for this one.
• Specifying a single-zone system where the spaces needed independent control, so half the building is never comfortable.
• Defaulting to gas heat where a heat pump fit the climate, the rates, and the electrification goal.
• Building a central plant on a small building, where the first cost and water-side maintenance overrun any efficiency it returns.
• Spreading distributed units across a large building past the point where a central plant would have cost less to run and been easier to maintain.
• Choosing a recirculating zone system, mini-split, fan coil, VRF, or PTAC, without planning the outdoor-air and ventilation path.
• Comparing systems on first cost alone and never running the life-cycle cost the building near the crossover actually needs.
• Comparing efficiency across the wrong metrics, or across the SEER-to-SEER2 change, and drawing the wrong conclusion.

Selection field checklist

Standards and references

The ASHRAE Handbook, HVAC Systems and Equipment, is the reference that classifies these families and lays out how each is applied, and ASHRAE Standard 90.1 sets the minimum equipment efficiencies that commercial systems have to meet. The adopted energy code in the jurisdiction is what makes those minimums enforceable, and they tighten most cycles, so confirm the adopted edition and any state amendments before you rely on a number.

Ventilation rates come from ASHRAE Standard 62.1 for commercial spaces and 62.2 for dwellings. Load and equipment selection on residential and light-commercial work follow the ACCA manuals, Manual J for the load calculation and Manual S for equipment selection, with Manual D for duct design. Equipment is rated under AHRI standards, the unitary standards for packaged and split DX and AHRI 550/590 for chillers, and the manufacturer's data and the project specification govern the specifics of any given unit.

Refrigerant safety, charge limits, and ventilation follow ASHRAE Standard 15 and the adopted refrigerant and mechanical codes, which are in flux as the industry moves to A2L refrigerants, so verify the current requirements for the refrigerant the equipment uses. Where the spec or the equipment listing is stricter than a code minimum or a rule of thumb, the stricter requirement controls.

Units, terms, and synonyms

The system families carry a pile of names and units, and the same idea reads differently across a drawing set, an equipment schedule, and a manufacturer cut sheet.

Cooling capacity is given in tons, where one ton is 12,000 BTU per hour, or in BTU per hour or kW directly. Cooling efficiency shows up as SEER2 and EER2 on unitary equipment, IEER for commercial part load, and kW per ton or IPLV on chillers. Heating efficiency is HSPF2 on heat pumps and AFUE on furnaces and boilers. DX is direct expansion, the refrigerant-at-the-coil approach. VRF and VRV are the same variable-refrigerant-flow technology. An RTU is a rooftop unit, an AHU an air handling unit, an FCU a fan coil unit, a WSHP a water-source heat pump, and a DOAS a dedicated outdoor air system.

All-air / all-water / DX

The three distribution carriers: conditioned air in duct, hot or chilled water in pipe, or refrigerant in line sets

Packaged vs split

Whole refrigeration circuit in one cabinet, versus an indoor unit and outdoor unit joined by a refrigerant line set

Central vs decentralized

One plant serving the building, versus a unit at or near each zone

VRF / VRV

Variable refrigerant flow, one outdoor unit feeding many indoor units, often with heat recovery

RTU / AHU / FCU

Rooftop unit, air handling unit, and fan coil unit, the common air-side equipment names

DOAS

Dedicated outdoor air system, which conditions ventilation air separately from the zone heating and cooling

Ton

12,000 BTU per hour of heating or cooling capacity

Related tools

Calculators and readiness checks for this work

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FAQ

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