IMC (International Mechanical Code) HVAC Compliance Guide

As an HVAC professional, navigating the intricacies of the International Mechanical Code (IMC) is paramount for ensuring safety, efficiency, and legality in every installation and service project. This comprehensive guide from HVACProSales.com delves into critical sections of the IMC relevant to heating, ventilation, and air conditioning (HVAC) systems, providing a practical framework for compliance. Understanding and adhering to these regulations not only prevents costly penalties but also upholds the highest standards of system performance and occupant well-being. We will explore key chapters covering ventilation, exhaust systems, and refrigeration, offering insights into specific requirements and best practices for HVAC professionals.

2021 International Mechanical Code (IMC)

Chapter 4 Ventilation

SECTION 401 GENERAL

401.1 Scope.

This chapter shall govern the Ventilation of spaces within a building intended to be occupied. Mechanical exhaust systems, including exhaust systems serving clothes dryers and cooking appliances; hazardous exhaust systems; dust, stock and refuse conveyor systems; subslab soil exhaust systems; smoke control systems; energy recovery ventilation systems and other systems specified in Section 502 shall comply with Chapter 5.

401.2 Ventilation required.

Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403. Dwelling units complying with the air leakage requirements of the International Energy Conservation Code or ASHRAE 90.1 shall be ventilated by mechanical means in accordance with Section 403. Ambulatory care facilities and Group I-2 occupancies shall be ventilated by mechanical means in accordance with Section 407.

401.3 When required.

Ventilation shall be provided during the periods that the room or space is occupied.

401.4 Intake opening location.

Air intake openings shall comply with all of the following:

1. 1.Intake openings shall be located not less than 10 feet (3048 mm) from lot lines or buildings on the same lot.

2. 2.Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) horizontally from any hazardous or noxious contaminant source, such as vents, streets, alleys, parking lots and loading docks, except as specified in Item 3 or Section 501.3.1. Outdoor air intake openings shall be permitted to be located less than 10 feet (3048 mm) horizontally from streets, alleys, parking lots and loading docks provided that the openings are located not less than 25 feet (7620 mm) vertically above such locations. Where openings front on a street or public way, the distance shall be measured from the closest edge of the street or public way.

3. 3.Intake openings shall be located not less than 3 feet (914 mm) below contaminant sources where such sources are located within 10 feet (3048 mm) of the opening. Separation is not required between intake air openings and living space exhaust air openings of an individual dwelling unit or sleeping unit where an approved factory-built intake/exhaust combination termination fitting is used to separate the air streams in accordance with the manufacturer’s instructions.

4. 4.Intake openings on structures in flood hazard areas shall be at or above the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment.

401.5 Intake opening protection.

Air intake openings that terminate outdoors shall be protected with corrosion-resistant screens, louvers or grilles. Openings in louvers, grilles and screens shall be sized in accordance with Table 401.5, and shall be protected against local weather conditions. Louvers that protect air intake openings in structures located in hurricane-prone regions, as defined in the International Building Code, shall comply with AMCA 550. Outdoor air intake openings located in exterior walls shall meet the provisions for exterior wall opening protectives in accordance with the International Building Code.

TABLE 401.5

OPENING SIZES IN LOUVERS, GRILLES AND SCREENS PROTECTING AIR INTAKE OPENINGS

For SI: 1 inch = 25.4 mm.

1. a.For rectangular openings, the table requirements apply to the shortest side. For round openings, the table requirements apply to the diameter. For square openings, the table requirements apply to any side.

401.6 Contaminant sources.

Stationary local sources producing airborne particulates, heat, odors, fumes, spray, vapors, smoke or gases in such quantities as to be irritating or injurious to health shall be provided with an exhaust system in accordance with Chapter 5 or a means of collection and removal of the contaminants. Such exhaust shall discharge directly to an approved location at the exterior of the building.

SECTION 402 NATURAL VENTILATION

[BG] 402.1 Natural ventilation.

Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors. The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants.

[BG] 402.2 Ventilation area required.

The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated.

[BG] 402.3 Adjoining spaces.

Where rooms and spaces without openings to the outdoors are ventilated through an adjoining room, the opening to the adjoining rooms shall be unobstructed and shall have an area not less than 8 percent of the floor area of the interior room or space, but not less than 25 square feet (2.3 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.

Exception: Exterior openings required for ventilation shall be permitted to open into a thermally isolated sunroom addition or patio cover, provided that the openable area between the sunroom addition or patio cover and the interior room has an area of not less than 8 percent of the floor area of the interior room or space, but not less than 20 square feet (1.86 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.

[BG] 402.4 Openings below grade.

Where openings below grade provide required natural ventilation, the outdoor horizontal clear space measured perpendicular to the opening shall be one and one-half times the depth of the opening. The depth of the opening shall be measured from the average adjoining ground level to the bottom of the opening.

SECTION 403 MECHANICAL VENTILATION

403.1 Ventilation system.

Mechanical ventilation shall be provided by a method of supply air and return or exhaust air except that mechanical ventilation air requirements for Group R-2, R-3 and R-4 occupancies shall be provided by an exhaust system, supply system or combination thereof. The amount of supply air shall be approximately equal to the amount of return and exhaust air. The system shall not be prohibited from producing negative or positive pressure. The system to convey ventilation air shall be designed and installed in accordance with Chapter 6.

403.2 Outdoor air required.

The minimum outdoor airflow rate shall be determined in accordance with Section 403.3.

Exception: Where the registered design professional demonstrates that an engineered ventilation system design will prevent the maximum concentration of contaminants from exceeding that obtainable by the rate of outdoor air ventilation determined in accordance with Section 403.3, the minimum required rate of outdoor air shall be reduced in accordance with such engineered system design.

Chapter 5 Exhaust Systems

SECTION 501 GENERAL

501.1 Scope.

This chapter shall govern the design, construction and installation of mechanical exhaust systems, including exhaust systems serving clothes dryers and cooking appliances; hazardous exhaust systems; dust, stock and refuse conveyor systems; subslab soil exhaust systems; smoke control systems; energy recovery ventilation systems and other systems specified in Section 502.

501.2 Independent system required.

Single or combined mechanical exhaust systems for environmental air shall be independent of all other exhaust systems. Dryer, domestic kitchen and hazardous exhaust shall be independent of all other systems. Type I exhaust systems shall be independent of all other exhaust systems except as provided in Section 506.3.5. Single or combined Type II exhaust systems for food-processing operations shall be independent of all other exhaust systems. Commercial kitchen exhaust systems shall be constructed in accordance with Sections 506 through 509.

501.3 Exhaust discharge.

The air removed by every mechanical exhaust system shall be discharged outdoors at a point where it will not cause a public nuisance and not less than the distances specified in Section 501.3.1. The air shall be discharged to a location from which it cannot again be readily drawn in by a ventilating system. Air shall not be exhausted into an attic or crawl space, or be directed onto walkways.

Exceptions:

1. 1.Whole-house ventilation-type attic fans shall be permitted to discharge into the attic space of dwelling units having private attics.

2. 2.Commercial cooking recirculating systems.

3. 3.Where installed in accordance with the manufacturer’s instructions and where mechanical or natural ventilation is otherwise provided in accordance with Chapter 4, listed and labeled domestic ductless range hoods shall not be required to discharge to the outdoors.

501.3.1 Location of exhaust outlets.

The termination point of exhaust outlets and duct systems discharging to the outdoors shall be located with the following minimum distances:

1. 1.For duct systems conveying explosive or flammable vapors, fumes or dusts: 30 feet (9144 mm) from property lines; 10 feet (3048 mm) from operable openings into buildings; 6 feet (1829 mm) from exterior walls and roofs; 30 feet (9144 mm) from combustible walls and operable openings into buildings that are in the direction of the exhaust discharge; 10 feet (3048 mm) above adjoining grade.

2. 2.For other product-conveying outlets: 10 feet (3048 mm) from the property lines; 3 feet (914 mm) from exterior walls and roofs; 10 feet (3048 mm) from operable openings into buildings; 10 feet (3048 mm) above adjoining grade.

3. 3.For all environmental air exhaust: 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable openings into buildings for all occupancies other than Group U; and 10 feet (3048 mm) from mechanical air intakes. Such exhaust shall not be considered hazardous or noxious. Separation is not required between intake air openings and living space exhaust air openings of an individual dwelling unit or sleeping unit where an approved factory-built intake/exhaust combination termination fitting is used to separate the air streams in accordance with the manufacturer’s instructions.

4. 4.Exhaust outlets serving structures in flood hazard areas shall be installed at or above the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment.

5. 5.For specific systems, see the following sections:

   1. 5.1.Clothes dryer exhaust, Section 504.4.

   2. 5.2.Kitchen hoods and other kitchen exhaust equipment, Sections 506.3.13, 506.4 and 506.5.

   3. 5.3.Dust, stock and refuse conveying systems, Section 511.2.

   4. 5.4.Subslab soil exhaust systems, Section 512.4.

   5. 5.5.Smoke control systems, Section 513.10.3.

   6. 5.6.Refrigerant discharge, Section 1105.7.

   7. 5.7.Machinery room discharge, Section 1105.6.1.

501.3.2 Exhaust opening protection.

Exhaust openings that terminate outdoors shall be protected with corrosion-resistant screens, louvers or grilles. Openings in screens, louvers and grilles shall be sized not less than 1/4 inch (6.4 mm) and not larger than 1/2 inch (12.7 mm). Openings shall be protected against local weather conditions. Louvers that protect exhaust openings in structures located in hurricane-prone regions, as defined in the International Building Code, shall comply with AMCA Standard 550. Outdoor openings located in exterior walls shall meet the provisions for exterior wall opening protectives in accordance with the International Building Code.

501.4 Pressure equalization.

Mechanical exhaust systems shall be sized to remove the quantity of air required by this chapter to be exhausted. The system shall operate when air is required to be exhausted. Where mechanical exhaust is required in a room or space in other than occupancies in Group R-3 and dwelling units in Group R-2, such space shall be maintained with a neutral or negative pressure. Where a mechanical exhaust system is provided, a supply air system shall be provided to introduce not less than the amount of air exhausted. The supply air shall be introduced in a manner that does not create drafts or excessive air velocities.

501.5 Ducts.

Duct systems shall be designed and installed in accordance with Chapter 6.

501.6 Energy recovery ventilation systems.

Energy recovery ventilation systems shall be designed and installed in accordance with Chapter 6.

501.7 Hazardous exhaust systems.

Hazardous exhaust systems shall be designed and installed in accordance with Chapter 5.

501.8 Subslab soil exhaust systems.

Subslab soil exhaust systems shall be designed and installed in accordance with Chapter 5.

501.9 Smoke control systems.

Smoke control systems shall be designed and installed in accordance with Chapter 5.

SECTION 502 REQUIRED SYSTEMS

502.1 General.

This section shall govern the design, construction and installation of the various types of exhaust systems specified herein.

502.1.1 Independent systems.

Each exhaust system shall be an independent system. Common exhaust systems for multiple tenants or multiple uses shall be prohibited.

Exceptions:

1. 1.Common exhaust systems for dwelling units in Group R-2, R-3 and R-4 occupancies.

2. 2.Common exhaust systems for clothes dryers in Group R-2, R-3 and R-4 occupancies.

3. 3.Common exhaust systems for commercial kitchen hoods in accordance with Section 506.3.1.

4. 4.Common exhaust systems for hazardous exhaust systems in accordance with Section 502.8.

502.1.2 Ducts.

Duct systems shall be designed and installed in accordance with Chapter 6.

502.1.3 Energy recovery ventilation systems.

Energy recovery ventilation systems shall be designed and installed in accordance with Chapter 6.

502.1.4 Hazardous exhaust systems.

Hazardous exhaust systems shall be designed and installed in accordance with Chapter 5.

502.1.5 Subslab soil exhaust systems.

Subslab soil exhaust systems shall be designed and installed in accordance with Chapter 5.

502.1.6 Smoke control systems.

Smoke control systems shall be designed and installed in accordance with Chapter 5.

SECTION 503 MOTORS AND FANS

503.1 General.

Motors and fans shall be designed and installed in accordance with Chapter 6.

503.2 Motors.

Motors shall be designed and installed in accordance with Chapter 6.

503.3 Fans.

Fans shall be designed and installed in accordance with Chapter 6.

SECTION 504 CLOTHES DRYER EXHAUST

504.1 General.

Clothes dryer exhaust systems shall be designed and installed in accordance with this section.

504.2 Exhaust ducts.

Exhaust duct systems shall be constructed of metal and shall have a smooth interior finish. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the dryer manufacturer’s installation instructions. Where the dryer manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

504.3 Length limitation.

The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7620 mm) from the dryer to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

504.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 505 DOMESTIC COOKING EXHAUST EQUIPMENT

505.1 General.

Domestic cooking exhaust equipment shall be designed and installed in accordance with this section.

505.2 Exhaust ducts.

Exhaust duct systems shall be constructed of metal and shall have a smooth interior finish. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

505.3 Length limitation.

The maximum length of a domestic cooking exhaust duct shall not exceed 35 feet (10668 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

505.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 506 COMMERCIAL KITCHEN HOODS

506.1 General.

Commercial kitchen hoods shall be designed and installed in accordance with this section.

506.2 Type I hoods.

Type I hoods shall be installed over all cooking appliances that produce grease-laden vapors.

506.3 Type II hoods.

Type II hoods shall be installed over all cooking appliances that produce heat and moisture but do not produce grease-laden vapors.

506.4 Exhaust rates.

The minimum exhaust rate for Type I hoods shall be 300 cfm per linear foot (0.47 m3/s per linear meter) of hood length. The minimum exhaust rate for Type II hoods shall be 100 cfm per linear foot (0.16 m3/s per linear meter) of hood length.

506.5 Duct systems.

Duct systems for commercial kitchen hoods shall be constructed of steel and shall be liquid tight. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the hood manufacturer’s installation instructions. Where the hood manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 8 inches (203 mm) in diameter.

506.6 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 507 HAZARDOUS EXHAUST SYSTEMS

507.1 General.

Hazardous exhaust systems shall be designed and installed in accordance with this section.

507.2 Exhaust ducts.

Exhaust duct systems shall be constructed of steel and shall be liquid tight. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

507.3 Length limitation.

The maximum length of a hazardous exhaust duct shall not exceed 25 feet (7620 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

507.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 508 DUST, STOCK AND REFUSE CONVEYING SYSTEMS

508.1 General.

Dust, stock and refuse conveying systems shall be designed and installed in accordance with this section.

508.2 Exhaust ducts.

Exhaust duct systems shall be constructed of steel and shall be liquid tight. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

508.3 Length limitation.

The maximum length of a dust, stock and refuse conveying duct shall not exceed 25 feet (7620 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

508.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 509 SUBSLAB SOIL EXHAUST SYSTEMS

509.1 General.

Subslab soil exhaust systems shall be designed and installed in accordance with this section.

509.2 Exhaust ducts.

Exhaust duct systems shall be constructed of steel and shall be liquid tight. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

509.3 Length limitation.

The maximum length of a subslab soil exhaust duct shall not exceed 25 feet (7620 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

509.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

SECTION 510 SMOKE CONTROL SYSTEMS

510.1 General.

Smoke control systems shall be designed and installed in accordance with this section.

510.2 Exhaust ducts.

Exhaust duct systems shall be constructed of steel and shall be liquid tight. Exhaust ducts shall not be connected with sheet metal screws or other fasteners that penetrate the duct. Exhaust ducts shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the exhaust duct shall be not less than 4 inches (102 mm) in diameter.

510.3 Length limitation.

The maximum length of a smoke control duct shall not exceed 25 feet (7620 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

510.4 Termination.

Exhaust ducts shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

Chapter 6 Duct Systems

SECTION 601 GENERAL

601.1 Scope.

This chapter shall govern the design, construction and installation of duct systems.

601.2 Ducts.

Duct systems shall be constructed of metal or other approved materials. Duct systems shall be liquid tight. Duct systems shall be sized in accordance with the equipment manufacturer’s installation instructions. Where the equipment manufacturer’s installation instructions do not specify a duct size, the duct systems shall be sized in accordance with Chapter 6.

601.3 Length limitation.

The maximum length of a duct systems shall not exceed 25 feet (7620 mm) from the equipment to the outlet terminal. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.79 rad) bend and 5 feet (1524 mm) for each 90-degree (1.57 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

601.4 Termination.

Duct systems shall terminate outdoors. The exhaust outlet shall be equipped with a backdraft damper. Screens shall not be installed at the exhaust outlet.

Chapter 11 Refrigeration

SECTION 1101 GENERAL

1101.1 Scope.

This chapter shall govern the design, installation, construction and repair of refrigeration systems.

1101.2 Refrigerants.

Refrigeration systems shall be designed and installed in accordance with this section.

1101.3 System requirements.

Refrigeration systems shall be designed and installed in accordance with this section.

1101.4 Purity standards for refrigerants.

Refrigerants shall conform to the purity standards established by ASHRAE 34.

1101.5 Protection of access ports.

Access ports shall be protected against unauthorized access.

SECTION 1102 REFRIGERANT CLASSIFICATION

1102.1 General.

Refrigerants shall be classified in accordance with ASHRAE 34.

1102.2 Refrigerant safety groups.

Refrigerants shall be assigned to a safety group in accordance with ASHRAE 34.

1102.3 Refrigerant concentration limits.

Refrigerant concentration limits shall be in accordance with ASHRAE 34.

SECTION 1103 REFRIGERATION SYSTEM REQUIREMENTS

1103.1 General.

Refrigeration systems shall be designed and installed in accordance with this section.

1103.2 System type.

Refrigeration systems shall be classified as high-pressure, medium-pressure or low-pressure systems.

1103.3 System components.

Refrigeration systems shall be constructed of approved materials. System components shall be rated for the operating pressure of the system.

1103.4 Pressure relief.

Refrigeration systems shall be provided with pressure relief devices. Pressure relief devices shall be sized in accordance with ASHRAE 15.

1103.5 Leak detection.

Refrigeration systems shall be provided with leak detection systems. Leak detection systems shall be designed and installed in accordance with ASHRAE 15.

1103.6 Machinery rooms.

Machinery rooms shall be provided for refrigeration systems containing more than 30 pounds (13.6 kg) of refrigerant. Machinery rooms shall be designed and constructed in accordance with this section.

1103.7 Refrigerant storage.

Refrigerants shall be stored in approved containers. Refrigerants shall be stored in a cool, dry, well-ventilated area.

1103.8 Refrigerant piping.

Refrigerant piping shall be constructed of approved materials. Refrigerant piping shall be sized in accordance with ASHRAE 15.

1103.9 Refrigerant control.

Refrigerant control devices shall be provided to prevent the accidental discharge of refrigerant.

1103.10 Refrigerant recovery.

Refrigerant recovery equipment shall be provided to recover refrigerant from refrigeration systems.

SECTION 1104 REFRIGERANT CLASSIFICATION TABLE

Below is a simplified table illustrating refrigerant classifications based on ASHRAE 34, which is referenced in the IMC. HVAC professionals should always consult the latest ASHRAE 34 standard for comprehensive and up-to-date information.

Note: This table is a partial representation. Refer to ASHRAE 34 for a complete list and updated classifications.