Terminology

• Ton: 12,000 Btu/h of cooling capacity
• DX: direct-expansion refrigerant cooling
• Gas/electric RTU: DX cooling with gas-fired heat
• Heat pump RTU: reversible refrigerant cycle for heating and cooling
• Economizer: dampers that use outdoor air for free cooling
• DOAS: dedicated outdoor air system; RTU-type unit treating ventilation air only
• Roof curb: insulated frame supporting the unit and its duct openings
• Curb adapter: transition for replacing units on existing curbs
• Downflow / horizontal discharge: supply and return through the curb or through side ducts
• SEER2 / IEER: cooling efficiency ratings for smaller and larger units
• Variable-speed compressor and fan: modulating capacity for part-load efficiency

Standards

Sizes

• Commercial RTUs range from small 3 to 5 ton units to large units of well over 50 tons
• Larger units trend lower cost per ton; crane, electrical, and curb costs added

Test standards

• AHRI 210/240 (smaller) and AHRI 340/360 (larger unitary equipment): efficiency ratings
• UL 1995 and UL 60335-2-40: equipment safety, including A2L refrigerant equipment
• ASHRAE 62.1: ventilation design
• ASHRAE 15 and 34: refrigerant safety and classification

Components

• Supply and return fans: variable-speed in modern units
• Compressors and condenser coils: DX cooling
• Heating section: gas furnace, electric heat, or heat pump
• Economizer and outdoor air dampers: with controls and sensors
• Filters: MERV-rated filter racks
• Optional energy recovery: wheel or plate sections

Detailing

• Confirm roof structure for unit weight and add framing at curbs
• Locate units away from roof edges, intakes, and noise-sensitive spaces
• Provide service clearances and walkway pads; plan crane access for replacement
• Keep outdoor air intakes away from exhausts, plumbing vents, and flues
• Coordinate roof drains and crickets around curbs
• Screen units for appearance and acoustics where needed

Uses

Specific uses

• Retail, restaurants, and big-box stores
• Single-story offices and schools
• Warehouses with office areas
• Medical office buildings
• DOAS ventilation for buildings with VRF or fan coils

Pros and cons

Pros

• Low first cost and simple installation
• No mechanical room space required
• Factory-packaged and tested
• Easy one-for-one replacement

Cons

• Roof penetrations and roof loads
• Noise and vibration near occupied spaces below
• Shorter service life than central plants
• Limited zoning per unit without VAV

Manufacturing and cost

Construction

• Units built and tested at the factory; shipped with curbs
• Set by crane; ductwork, gas, power, condensate, and controls connected

Main manufacturers and suppliers

• Carrier
• Trane
• Lennox
• York
• Daikin Applied
• AAON

Trade associations: ASHRAE and AHRI.

Typical costs

• Packaged RTU, installed: about $1,500 to $4,000 per ton; larger units about $1,800 to $2,500 per ton plus crane, electrical, and curb
• Small units (3 to 5 tons), installed: about $8,000 to $18,000

Sources

• Oxmaint: RTU replacement cost 2026, per-ton pricing, https://oxmaint.com/industries/hvac/rtu-replacement-cost-2026-per-ton-pricing-install-labor-hidden-costs
• PickHVAC: commercial rooftop unit cost by ton, 2026, https://www.pickhvac.com/?p=46314
• New York OGS: 23 74 13 packaged outdoor central-station AHU specification, https://online2.ogs.ny.gov/dnc/masterspec24/docs/Division23HeatingVentilatingAndAirConditioning/237413.0PackagedOutdoorCentralStationAirHandlingUnits.docx
• ICC: 2024 I-Code A2L related changes, https://iccsafe.org/wp-content/uploads/2024_I-Code_A2L_Related_Changes_FINAL_06.14.2024.pdf
• UpCodes: 2024 IMC Chapter 3 general regulations, https://up.codes/viewer/department-of-defense/imc-2024/chapter/3/general-regulations
• Wikimedia Commons: Helicopter delivering a rooftop HVAC unit -02- (9718240851).jpg, by Ben Schumin (CC BY-SA 2.0), https://commons.wikimedia.org/wiki/File:Helicopter_delivering_a_rooftop_HVAC_unit_-02-_(9718240851).jpg