Title 24 Economizer Requirements

The threshold, precisely

Section 140.4(e)1 applies to each cooling air handler with a design total mechanical cooling capacity over 33,000 Btu/hr, and to chilled-water cooling systems without a fan or that use induced airflow above the capacities in Table 140.4-C. Below the line, there is no economizer requirement from this provision. Above it, the air handler needs an air economizer that can supply 100 percent of the design supply air as outside air, or a water economizer, and because the test is on design capacity rather than physical size, a modest-looking unit can cross the line. It is read off the equipment schedule, not estimated from tonnage in conversation.

The exceptions to Section 140.4(e)1

• Special outside air filtration and treatment that makes compliance infeasible.
• Outdoor air cooling that would affect other systems, such as humidification, dehumidification or supermarket refrigeration, in a way that increases overall building LSC.
• Systems serving hotel and motel guestrooms.
• Comfort cooling systems that meet the efficiency improvements in Table 140.4-F.
• Fan systems primarily serving computer rooms, which have their own rule in Section 140.9(a).
• An air handler under 54,000 Btu/hr of design cooling capacity whose ventilation comes from a dedicated outdoor air system with exhaust air heat recovery that meets the heat recovery and minimum ventilation conditions in the exception.
• Controlled environment horticulture spaces where an air economizer would affect carbon dioxide enrichment, and systems complying with Section 140.4(a)3Ai and Aii.

Heat pumps are covered the same way

The text speaks of each cooling air handler, not of one kind of equipment, so a heat pump and an air conditioner of the same cooling capacity are treated alike. Choosing a heat pump for the heating side does not remove the cooling-side obligation, which is the single most common misconception about this requirement.

Alterations: Section 141.0(b)2C, Exception 6 and Table 141.0-E-1

When a space-conditioning system or component is new or replaced in an existing building, Section 141.0(b)2C requires it to meet the Section 140.4 requirements that apply to what is altered, so the 33,000 Btu/hr line comes with it. Exception 6 to Section 141.0(b)2C removes Section 140.4(e) for a system that is not a single package air-cooled commercial unitary air conditioner or heat pump and has a cooling capacity under 54,000 Btu/h. A single package unit is therefore not excused by that exception, whatever its size.

A new or replacement single zone packaged rooftop system with direct expansion cooling under 65,000 Btu/hr must instead meet Table 141.0-E-1 or the performance route. The table sets, by building type and climate zone, whether the unit needs a single zone heat pump with an economizer, an air conditioner with a furnace or a dual fuel heat pump with a variable speed fan and an economizer, or has no requirement. The economizer in each case is built to Section 140.4(e).

What an economizer does, and why the code wants one

It uses outdoor air for cooling when conditions allow, instead of running mechanical cooling. In a climate with long mild shoulder seasons that is a large amount of avoided compressor work, which is why the requirement attaches at a fairly modest capacity rather than only to large plant.

The acceptance test covers more than the economizer

The 2025 form NRCA-MCH-05-A covers economizer controls together with dedicated outdoor air systems and heat and energy recovery ventilation. So a project with an economizer and an HRV is not necessarily producing two separate certificates — but it is producing a test performed by a technician certified for mechanical acceptance testing.

One form is required for each system demonstrating compliance, so four rooftop units with economizers produce four.

On VAV systems the controls go further

For variable-air-volume systems the prescriptive route follows ASHRAE Guideline 36, which specifies an air economizer under direct digital control alongside static pressure setpoint reset and supply air temperature reset. On those systems the economizer is part of a defined control sequence rather than a standalone device.

Where it goes wrong

Sequences, not hardware. An economizer physically present but not controlling as the sequence requires fails the test, in the same way that outdoor air controlled by a fixed minimum damper position fails the outdoor air test. The equipment is the easy part.

Common Title 24 Questions

1. Does replacing commercial HVAC trigger Title 24?
2. Does a rooftop unit replacement require Title 24?
3. Do heat pumps affect commercial Title 24 compliance?
4. Does adding air conditioning trigger Title 24?
5. What are Title 24 lighting controls?
6. Commercial ventilation requirements under Title 24

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