Frequently asked questions about the economizer requirements for the 2025 Energy Code.
General Information
Section 140.4(e) of the 2025 Energy Code prescriptively requires each cooling air handler that has a design total mechanical cooling capacity over 33,000 Btu/hr or chilled-water cooling systems without a fan or that use induced airflow that has a cooling capacity greater than the systems listed in Table 140.4-C, shall include either an air economizer capable of modulating outside-air and return-air dampers to supply 100 percent of the design supply air quantity as outside air; or a water economizer capable of providing 100 percent of the expected system cooling load at outside air temperatures of 50°F dry-bulb and 45°F wet-bulb and below with five exceptions (see accordion describing exceptions below).
Table 140.4-C – Chilled Water System Cooling Capacity
Total Building Chilled Water System Capacity, Minus Capacity of the Cooling units with Air Economizers
| Climate Zones | Building Water-Cooled Chilled Water System | Air-Cooled Chilled Water Systems or District Chilled Water Systems |
| 15 | ≥ 960,000 Btu/h (280 kW) | ≥ 1,250,000 Btu/h (365 kW) |
| 1-14 | ≥ 720,000 Btu/h (210 kW) | ≥ 940,000 Btu/h (275 kW) |
| 16 | ≥ 1,320,000 Btu/h (385 kW) | ≥ 1,720,000 Bu/h (505 kW) |
Yes. There are eight exceptions that exclude prescriptive economizer requirements
- Where special outside air filtration and treatment, for the reduction and treatment of unusual outdoor contaminants, makes compliance infeasible. Minimum required solar PV system capacity is less than 4 kWdc.
- Where the use of outdoor air for cooling will affect other systems, such as humidification, dehumidification, or supermarket refrigeration systems, so as to increase overall building LSC.
- Systems serving hotel/motel guestrooms.
- Where comfort cooling systems have the cooling efficiency that meets or exceeds the cooling efficiency improvement requirements in Table 140.4-F.
- Fan systems primarily serving computer rooms.
- In all climate zones, each air handler that has a design total mechanical cooling capacity less than 54,000 Btu/hr where ventilation is provided by a dedicated outdoor air system (DOAS) with exhaust air heat recovery in accordance with Section 140.4(p), and the following:
- The DOAS unit shall meet the exhaust air heat recovery ratio as specified in Section 140.4(q)1 and include bypass or control to disable energy recovery as specified in Section 140.4(q)2.
- The DOAS unit shall provide at least the minimum ventilation air flow rate as specified in Section 120.1(c)3 and provide no less than 0.3 cfm/ft2 during economizer conditions.
- Where the use of an air economizer in controlled environment horticulture spaces will affect carbon dioxide enrichment systems.
- Systems complying with Sections 140.4(a)3Ai and 140.4(a)3Aii.
Frequently Asked Questions
Yes. A newly installed economizer added to an existing chilled water-cooling system would need to meet Section 140.4(e). Per newly added Exception 6 to Section 141.0(b)2C the economizer prescriptive requirements in Section 140.4(e) are not applicable to the single package air-cooled commercial unitary air conditioners or heat pumps, with cooling capacity less than 54,000 Btu/h.
No. The total design capacity is the total rated capacity of the equipment. Per Section 140.4(e) each cooling air handler that has a design total mechanical cooling capacity over 33,000 Btu/hr must comply with economizer prescriptive requirements unless it meets an exception. Consider the performance approach to model this project to trade-off the economizer requirements with other efficiencies.
Yes. Exception 6 to § 141.0(b)2C requires single packaged aircooled commercial unitary air conditioners or heat pumps with cooling capacity less than 54,000 Btu per hour to meet the economizer requirements in § 140.4(e). This exception does not require economizers for replacements of VRF, split systems, or systems that are not single packaged units.
No. Replacing the chiller equipment alone does not trigger the economizer requirements in Section 140.9(a).
No. It cannot be integrated to cool simultaneously with the chillers.
Yes. In addition, the economizer must be equipped with a fault detection and diagnostic system. However, the requirement for an economizer can be waived if the AC unit’s efficiency is at least 30% more efficient than the minimum cooling efficiency requirement. Refer to Table 140.4-F.