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THE TECHNICAL TIMES Proper Venting Is A Must When quality heating equipment is selected and installed, see to it that it is properly piped, wired, suspended, and vented. This will ensure a worry free heating system that is economical to operate. But, if any one of these areas is ignored, trouble will follow. A common issue is improper, or poor venting. A heating system is only as good as the venting system it is connected to. A poor vent system cannot only cause problems with proper combustion of the fuel being burned, but can also lead to spillage or leakage of the products of combustion into the heated space. Compounding this issue is changes to the standards governing unit heaters in North America. Recently CSA International Requirement 10.96 and CR 96-005 were combined with ANSI Z83.8 / CSA 2.6 to create one over-arching standard for all unit heaters sold in the United States and Canada. One major change that affects many end users is retraction of an exemption that allowed Category I Horizontal venting in some Residential applications, which became effective July 1, 2011. What does this mean? All power vented unit heaters installed in Residential applications that require horizontal venting must now conform to Category III venting requirements. This means that the vent system must be gas tight and meet certain construction criteria, as defined in UL1738, the standard for Venting Systems for Gas Burning Appliances, Categories II, III, & IV. Venting systems that are approved to meet the UL1738 standard can be found on Underwriters Laboratory’s website and will be clearly marked with UL approval. These systems tend to make installation as easy as possible, with integral seals and fasteners to ensure a perfect installation every time. This change in venting code
applies to all manufacturers of Gas Fired Unit Heaters. Power vented units installed in Commercial or Industrial applications may be installed with either a listed vent system as described above or with properly sealed single wall metal vent pipe, as described in the Installation & Service Manual. This applies to separated combustion units as well. High efficiency (model PTC) separated combustion units are condensing appliances, which means that the vents must be gas and water tight, as well as include means to drain the condensate from the vent system. The vent temperature for these units are significantly lower than those of a power vented or separated combustion unit, consequently the venting for these units is PVC and can simply be primed and glued together to create gas and water tight joints. Consult the Installation & Service Manual for more detailed instructions. There are several simple rules to follow to assure proper venting of power vented heating equipment. 1.
Keep vent runs as straight as possible with few turns or bends. 2. Never use a vent size smaller than the size recommended by the heating equipment manufacturer. 3. All vents must terminate with a proper vent cap. 4. Vertical vent systems must: a. Terminate vertically (up) b. Not have a horizontal run that is more than 75% of the vertical rise in Category I installations (Example: if the vent height is 10’, the horizontal portion of the vent system cannot exceed 7-1/2’).
c.
Terminate a reasonable distance above the roof to prevent snow buildup from blocking the vent terminal.
Figure 2.1 – Horizontal Venting Example
Figure 2.1 – Vertical Venting Example
6. Always provide a drip leg with a clean out cap, located appropriately based on the installation, to prevent condensate in the vent pipe from entering the heating equipment. 7. Special attention must be paid to the maximum and minimum allowed vent lengths in the Installation & Service Manual. 5. Horizontal vent systems must: a. Terminate horizontally (sideways) b. Be pitched a minimum ¼” per foot (either up or down). c. Not terminate near air inlet openings to the structure. Make sure the vent is sufficiently high enough or guarded to prevent accidental contact by people or equipment.
For additional information, consult the Manufacturer’s Installation and Service Manual, the National Fuel Gas Code NFPA 54 (ANSI Z223.1), and/or any pertinent local codes.
Commercial Products Group Modine Manufacturing Company 1500 DeKoven Avenue Racine, WI USA 53403-2552 Phone: 1.800.828.4328 (HEAT) www.modinehvac.com © Modine Manufacturing Company 2012
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