Significant changes to the commercial provisions in 2012 IECC


Mechanical systems

Several changes were made to mechanical system requirements in the update from the 2009 to 2012 IECC. More equipment was added to Tables C403.2.3(1) through (8) and values were modified—mostly to be more restrictive, which could increase the costs of construction. Table C403.2.3(5) was modified to decrease minimum gas and oil-fired boiler efficiencies, however. Liquid-to-liquid heat exchangers must now meet the test procedure AHRI 400 (Table C403.2.3(9)).

Section C403.2.3.1, Water-Cooled Centrifugal Chilling Packages, an exception to Section 503.2.2 in the 2009 IECC, is now its own subsection. The Adjusted Maximum Full Load kW/ton was replaced with the Adjusted Minimum Full-Load coefficient of performance (COP). The equations defining terms have changed to be functions of Celsius instead of Fahrenheit and refer the user to Table 6.8.1C of AHRI Standard 550/590 instead of Table 503.2.3(7). The range of fluid temperature leaving the evaporator and condenser was increased from 38 to 102 F to 36 to 115 F, and a lift between 20 to 80 F is now required for this section to be applicable.

Automatic start controls capable of automatically adjusting the daily start time of the HVAC system are required for each HVAC system (C403. The occupant load requirement for demand control ventilation (C403.2.5.1) was lowered from 40 people to 25 people per 1000 sq ft, however an additional exception was added excluding the demand-controlled ventilation provided for process loads only.

Fans and air movement

The scope of the prescriptive HVAC systems and equipment requirements (C403.3) expanded due to the removal of the second paragraph exempting certain fan systems. Variable air volume (VAV) fan control (C403.4.2) expanded the applicability of the section from VAV fans with motors ≥10 hp to motors ≥7.5 hp; however, an additional exception was added excluding vane-axial fans with variable-pitch blades. Static pressure sensors used to control VAV fans shall be positioned such that the controller setpoint is ≤1/3 the total design fan static pressure with the exception of systems with zone reset controls (C403.4.2.1). Sensors located past duct splits need a sensor in each major branch.

Some exceptions to energy recovery ventilation system requirements were modified (C403.2.6). Exception 3 was modified to also require that the exempt space not be cooled, and exceptions 5 and 6 now refer to climate zones instead of specific climate qualities. Furthermore, exception 8 was added which excludes systems where the largest source of air exhausted at a single location at the building exterior is <75% of the design outdoor airflow rate, and exception 9 was added that excludes systems expected to operate <20 hours/week at the outdoor air percentage covered by Table C403.2.6. Single-zone VAV systems must now comply with the constant volume fan power limitation (C403.2.10.1) with the newly added exception of vivariums. Exception 3 excluding fans exhausting air from fume hoods in the 2009 edition was deleted, and additional devices were added to Table C403.2.10.1(2), Fan Power Limitation Pressure Drop Adjustment.


The entire Economizer Requirements section (C403.3) and all of its subsections were modified extensively in the 2012 update. Exceptions to the requirements were added including systems expected to operate <20 hours/week, systems that serve residential spaces where system capacity is less than five times the requirement listed in Table C403.3.1(1), and others. Climate zones 2A, 7, and 8 now require economizers (Table C403.3.1(1)), and the economizer requirement was also made more stringent by decreasing the cooling system requirement from 54,000 Btu/h to 33,000 Btu/h.

Compliance with Sections C403. through 4 is mandatory, and Section C403. requires that economizer damper sequencing with mechanical cooling equipment cannot be controlled by only mixed air temperature except for systems controlled from space temperature, such as single-zone systems. Section C403., High-Limit Shutoff, now refers users to newly added tables C403. and (2), and section C403. requires excess air relief to avoid over pressurization. Economizer Design (C403.4.1) limits the maximum water-side pressure drop to 15 ft of water, and economizer systems are required to be integrated with mechanical cooling systems. Economizers also cannot increase building heating energy use.

Pools and spas

The section and subsections regarding pools (C404.7) were expanded to include in-ground spas. Heaters are required to have an on/off switch mounted outside the heater. Section C404.7.2 was modified for clarity to include built-in timers. Pools heated >90 F are no longer required to have a cover with a minimum insulation value of R‑12, and the exception for vapor retardant covers was made more stringent by increasing the site-recovered energy used for heating from 60% to 70%.


Mechanical Systems Commissioning and Completion Requirements (C403.2.9) is a new section that introduces the added Section C408, System Commissioning. Section C408 covers commissioning of the building mechanical systems and electrical power and lighting systems, and it contains requirements that are aimed to be more process-oriented. Mechanical systems in buildings where the total mechanical equipment heating and cooling capacities are less than 600,000 Btu/h and 480,000 Btu/h, respectively, and systems serving dwelling units in hotels, motels, and boarding houses are exempt. Requirements concerning commissioning plans, system balancing, functional testing, and reports/documentation are specified, and mechanical commissioning must be completed prior to passing the final mechanical inspection. Table 1 provides brief descriptions of the individual commissioning and completion requirements within Section C408.

Table 1: Newly added section C408 contains all of the systems commissioning requirements. Courtesy: A S Klein Engineering

As the 2012 International family of codes is adopted, it is imperative that design professionals understand the changes since previous editions and the impacts they have on construction. This article touched briefly on all significant changes and points the reader to the appropriate sections of the code for further detail and context.

Andrew Klein is president of A S Klein Engineering, a professional engineering firm that represents businesses and organizations throughout the building code and standard development process. The firm provides technical committee representation, building code advocacy, and building code consulting services.

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LAWRENCE , PA, United States, 10/25/13 05:01 PM:

The article should state that very few states and jurisdictions are adopting the 2012 I Codes, and when they do, they are being amended. The reasons for not adopting are the Codes are that they are too complicated, too expensive, and cannot be fully enforced. Indeed, some states and jurisdictions are looking to move to a six year or longer code adoption cycle for these and other reasons. This move concerns the code writing groups, whose income is heavily dependent on selling books.
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