By / Norm Grusnick, PEng
Commercial Sales Rep, PACAIRE HVAC Suppliers Ltd.
Gas-fired equipment is changing and so are the related codes. As efficiencies and energy factors creep up, the installation processes and venting technologies evolve. New materials recently have presented the installers with a learning curve. As a gas appliance is only as good as the venting system; poor venting can cause improper combustion and possible gas spillage into the occupied space. As efficiencies are changing so are the various types of venting materials available, each for a specific application. There is polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), and polypropylene venting, as well more traditional metal venting systems.
Unit Heaters
Unit heaters are most often found in warehouses and semi-finished areas. Relatively recent code changes and energy efficiency concerns have seen some of the most significant shifts in venting for unit heaters.
Recently, Canadian Standards Association (CSA) requirement 10.96 and CR96-005 were combined with American Standards Institute (ANSI) Z83.8 CSA2.6 to create one overreaching standard for all unit heaters installed in North America. Going forward all new horizontally vented unit heaters will require a minimum Category III venting.
This means that all power-vented unit heaters installed in commercial applications that require horizontal venting must now be gas-tight and meet criteria defined in UL1738, Venting Systems for Gas Burning Appliances, Categories II,III,IV. Venting systems approved to meet UL1738 will be clearly identified on each piece with ULC approval.
Power-vented units installed in commercial applications must use a listed vent system. This applies to separated combustion units, as well. High-efficiency, separated combustion units are condensing appliances, meaning the vents must be gas and water tight and must include a means to drain condensate from the vent system.
There are a variety of simple rules to follow to ensure proper venting. Perhaps the most important is the need to keep vent runs as straight as possible, limiting the number of turns or elbows. And, never use a vent size smaller than the size recommended by the equipment manufacturer.
Vertical vent systems must terminate vertically, must not have a horizontal run that is more than 75 percent of the vertical rise in Category I installations, and must terminate a reasonable distance above the roof line to prevent snow buildup. Vertical venting systems are preferred as they interfere less with adjacent building occupants.
Horizontal vent systems, if needed, must terminate horizontally and must be pitched no less than a quarter inch per foot and must not terminate near inlet openings. They must also be at a height sufficient to prevent accidental contact by neighbours.
A drip leg is recommended with the cleanout cover located appropriately based on the installation to prevent condensate in the vent pipe from entering the heating equipment. Special attention must be paid to the maximum length of the vent system from the manufacturer’s installation instructions.
Boilers
The majority of gas-fired boilers are now Category IV and require positive pressure venting systems. Category I appliances feature less than 84 percent efficiency and operate with a neutral or negative pressure. The higher stack temperature—though less than 550 degrees F—means flue gas condensate is not an issue.
Category II appliances often use a small fan to move gases through a secondary heat exchanger. The force is not enough to pressurize the flue, thus operating at neutral or negative vent static pressure.
With vent gas temperatures below 140 degrees F over dew point, Category II appliances can cause excessive condensation in the vent.
Category III appliances operate with a positive pressure but are noncondensing, as vent gases are above 140 degrees F.
Category IV applies to high-efficiency condensing appliances producing condensate that must be removed.
One thing that has recently appeared is a big move towards polypropylene vent systems instead of PVC and CPVC. Component availability for polypropylene venting systems has greatly improved in the last few years and costs have come down. Polypropylene may be a better option for condensing boilers where flue temperatures tend to fluctuate. Polypropylene can operate up to 230 degrees F. As efficiency standards increase, the industry is providing more installer training to ensure appliances are vented correctly. ■
