August 1, 2023
From the 2024 UPC Illustrated Training Manual, Chapter 5 – WATER HEATERS
509.2.6 Direct-Vent Appliances. Listed direct vent appliances shall be installed in accordance with the manufacturer’s installation instructions. [NFPA 54:12.3.5.1]
The venting system of a direct-vent appliance is considered to be part of its listing. Listed appliances are tested with inlet and outlet configurations taken from their installation directions. Therefore, the installation instructions must be followed carefully. Section 509.8.2 provides requirements for the location of the vent terminations of direct-vent appliances.
Direct-vent gas appliances offer higher efficiency than natural vent gas appliances. Natural vent appliances use room air for combustion to provide air to fuel the fire. Direct-vent appliances utilize one of two styles of dual piping systems. The first method is the Co-Axial Pipe or Concentric Method, where a pipe within a pipe will bring combustion air from outside through the outer chamber and exhausts the products of combustion to the outside through the inner chamber (see Figure 509.2.6a). The second method, the Co-Linear Pipe Method, uses two separate pipes. One pipe brings in combustion (supply) air while the other pipe carries away the products of combustion to the outside (see Figure 509.2.6b).
The objective of the direct-vent appliance is to have no openings within the building. No vent collars (draft hoods) or combustion air openings are allowable within the building as part of a direct-vent appliance installation; however, these appliances are not necessarily sealed combustion chamber appliances unless they are specifically listed as such.
DIRECT VENT WATER HEATER USING A CONCENTRIC VENT AND SUPPLY
DIRECT VENT WATER HEATER CO-LINEAR PIPE METHOD
From the 2024 UMC Illustrated Training Manual, Chapter 9 – INSTALLATION OF SPECIFIC APPLIANCES
914.0 Non-Recirculating Direct Gas-Fired Industrial Air Heaters.
914.1 Application. Direct gas-fired heating and forced ventilation appliances for commercial and industrial applications shall be listed in accordance with the following standards as applicable:
(1) ANSI Z83.4/CSA 3.7.
(2) ANSI Z83.18. [NFPA 54:10.8.1]
An industrial direct-gas-fired heater is “a heater in which all the products of combustion generated by the burners are released into the airstream being heated.”
For various prescriptive code requirements, such as clearances to combustibles and accessibility, pertaining to the installation of non-recirculating and circulating directgas-fired industrial heaters, refer to the code, the appliance rating plate, and the manufacturers’ installation instructions. Figure 914.1 illustrates an industrial-type makeup air unit.
The purpose of the non-recirculating industrial air heater is to offset building heat loss by heating outside air only, while the circulating type offsets heat loss by heating outdoor air and, if applicable, indoor air.
These gas appliances are permitted in industrial or commercial occupancies only and, without exception, shall not serve any area serving sleeping quarters.
DIRECT-FIRED MAKEUP AIR HEATER
(This is not to be considered the official position of IAPMO, nor is it an official interpretation of the Codes.)
IAPMO
IAPMO develops and publishes the Uniform Plumbing Code®,the most widely recognized code of practice used by the plumbing industry worldwide; Uniform Mechanical Code®; Uniform Swimming Pool, Spa and Hot Tub Code®; and Uniform Solar Energy, Hydronics and Geothermal Code™ — the only plumbing, mechanical, solar energy and swimming pool codes designated by ANSI as American National Standards — and the Water Efficiency Standard (WE-Stand)™. IAPMO works with government, contractors, labor force, and manufacturers to produce product standards, technical manuals, personnel certification/educational programs and additional resources in order to meet the ever-evolving demands of the industry in protecting public health and safety.
Last modified: August 1, 2024