HPAC Magazine


October 1, 2013 | By Ian McTeer

Horizontal venting terminations have created a variety of problems. It is time to consider other options.

Likely about five minutes after our ancestors learned to control fire they realized the smoke would rise up and away, unless of course you are at a campfire with me in which case the smoke always comes my way. Eventually First Nations people in North America learned how to build an elegant conical shelter called a tipi (or tepee) with the ability to have a small fire for warmth and cooking inside at the same time. They realized the smoke would rise up and exit through a hole designed into the top of the tipi. The tipi even had smoke flaps to prevent downdrafts; it was an excellent chimney.

By the 19th century period of the Industrial Revolution, chimneys had become an iconic part of human progress. These days chimneys have taken on a more sinister status that ranges anywhere from toxic nuisance, to a symbol of rapacious capitalism. I still prefer to believe that chimneys serve a useful purpose and are essential to our well-being. However, in residential HVAC the chimney has in large part, been replaced by the horizontal vent. We still need to safely remove products of combustion from any fossil fueled appliance so there is no escaping the need for some type of venting process, either horizontal or vertical.

Vertical chimneys have some drawbacks for contractors and technicians especially when they do not work well during a cold winter. Horizontal venting is easier but I am still hearing horror stories about horizontal gas appliance venting with sidewall termination.


Going back to the early days of fuel oil combustion in boilers and gravity furnaces, the masonry chimney served as a fairly reliable conduit for flue gas to be conducted outdoors. Oil burners were not nearly as efficient as they are today so the temperature of the flue gas was typically high enough to ensure all the products of combustion were effectively removed from the building.

Starting in the 1960s, natural gas became the fuel of choice for many urban Canadian homeowners. It was reasonably inexpensive, required no storage tank, was cleaner burning, promised less appliance maintenance, and was very reliable. The first forced air gas furnaces were equipped with a draft hood designed to keep a neutral over-fire draft by allowing dilution air from the house to enter the furnace through a relief opening thus moderating the venting action. The draft hood also allowed flue products to spill into the building if the chimney or vent connector became blocked or restricted. Spillage also occurs when the appliance cannot find enough air for combustion during a burner cycle. As the flue spills into the area of the combustion chamber it is recycled through the combustion process creating further spillage with ever higher concentrations of CO, a process that must be avoided.

A draft hood equipped (and later fan assisted) gas fired appliance is classified as Category 1: an appliance that operates with a non-positive vent static pressure and with a flue loss not less than 17 per cent. That basically means the appliance cannot be more than 83 per cent efficient simply because moisture in the flue gas will easily condense in the venting system if more heat is removed.

It turns out that manufacturer estimates of combustion efficiency in the early days were wildly optimistic based on the test methods available at the time. Typically rated at 80 per cent AFUE, it was not until a new more thorough test method was devised that the industry discovered the early draft-hood equipped appliances were typically running anywhere from 25 per cent to 40 per cent flue loss. With so much heat in the flue it was not too difficult to retain buoyancy in a vertical chimney.

In 1989, the Province of Ontario’s Gas Utilization Code had this to say about gas appliances: “Every appliance shall be connected to either an effective chimney or vent…” and “masonry, concrete, or metal chimney shall be built and installed in accordance with the Provincial or Territorial Building Code. In the absence of such a code, then the National Building Code of Canada shall be used.”

By the late 1980s, manufacturers had figured out how to make more efficient Category 1 appliances using a fan assisted (induced draft) combustion process but higher AFUE means lower flue temperature. The moisture laden flue leaving these furnaces through single wall vent connectors into cold masonry chimneys was not effective; the classic vertical chimney as described in the Code needed help.

By May 1, 1993, the Province of Ontario and others had adopted a completely new set of rules for venting Category 1 gas appliances. The old Appendix B was replaced by Amendment 1 to the CAN/CGA-B149.1-M91 Installation Code. Talk about sweeping changes; the rules were numerous and complex. At the same time, governments and consumers demanded more efficient, tighter housing thus introducing a new concept: continuous depressurization. The new vertical venting rules included vent sizing tables for fan assisted, draft hood equipped and for appliances in situations where continuous depressurization up to 5 Pa might exist.

Canadian Standards Association (CSA) is now responsible for the B149 gas codes and even though the 80 per cent furnace has been legislated out of existence, the latest edition of code still has the tables published in Annex C. There are plenty of 80 per cent appliances working today in Canada and their vents/chimneys must conform to the tables.

Horizontal Venting

Since vertical venting of Category 1 appliances was causing so much grief, another type of 80 per cent AFUE gas furnace appeared in the late 1980s. Instead of fan assisted combustion, these units were power vented. Known as Category III appliances, the flue loss was still not less than 17 per cent but the vent was under a positive pressure created by the draft inducer. Because B-Vent and single wall metal pipe cannot be used in this application, two new types of venting materials were developed: stainless steel and the more commonly used, thermoplastic materials based on G.E.’s Ultem resin. With trade names like Ultravent and Plexvent, the 80 per cent furnaces approved to use this material quickly became popular with contractors, particularly in new construction. Builders liked the idea that by installing Category III appliances, a vertical chimney would no longer be required.

Authorities are clamping down on sidewall terminations.

• Alberta and Saskatchewan require horizontal termination points to be at least four feet (unobstructed) from the property line of the adjacent lot for an input over 35K btuh.

• If there is less than four feet then NO TYPE of termination is allowed. 

• If there is more than four feet, but less than eight feet, then the flu must be redirected as shown in Figure 1. 

• The State of Massachusetts, U.S. (among other things) requires a hard-wired CO detector with battery back-up and alarm to be installed in every job where a gas fuelled appliance has a sidewall termination that will be less than seven feet above grade

Whether or not the material was inherently defective or the installation instructions were ignored (or both), horizontally vented 80 per cent furnaces using high temperature plastic vent (HTPV) did not last long. Consumers reported cracking pipes, sagging vents, condensate leakage, joint failure, furnace problems, and the list went on. By September of 1995 the old Ontario Ministry of Consumer and Commercial Relations, Fuels Safety Branch (now TSSA) had issued an order to gas utilities not to supply gas to applia
nces vented with HTPV plastics after August 31, 1996. As you can imagine, lawsuits were launched by end-users in an effort to recover costs incurred to transition to alternative approved stainless steel vents or to new 90 per cent AFUE furnaces vented with ABS/PVC.Manufacturers and governments did help out with special programs, but the affected homeowners did ultimately bear the burden. That was an ugly situation and we do not want to go there again.

Since Then

Mid efficient gas furnaces largely disappeared from new construction after 1996. While mids were still popular in retrofit applications, some venting problems continued. Masonry chimneys had to be lined with a properly-sized aluminum liner (sometimes insulated) and Type B-1 material was often required for the vent connector. It has been getting complicated in Canadian homes: HRV’s, high volume kitchen exhaust fans, tight fitting windows and doors together with expanding foam insulation in seemingly every crack; this in addition to clothes driers, bathroom fans, central vacuum cleaners, Category III power vented water heaters, and other air exhausting appliances. The resulting depressurization makes the use of vertically vented Category 1 appliances undesirable.

In 1992 Canada’s Parliament passed the Energy Efficiency Act and the Energy Efficiency Regulations have been in force since 1995. This all-encompassing legislation requires most energy consuming appliances sold in Canada to use less of it. As a result of this Act, the installation of 80 per cent AFUE residential gas furnaces anywhere in Canada was prohibited after December 31, 2009.

Prior to 2010, 80 per cent AFUE furnaces still enjoyed a considerable share of the replacement market because they were less expensive to install in many situations. 90 per cent+ AFUE appliances have been around since the 1970s and now command the forced air market.

They are designated as Category IV – an appliance that operates with a positive vent static pressure with a flue loss less than 17 per cent. Most are horizontally vented using certified PVC plastic pipe. Until January 1, 2007 ABS plastic material was allowed for venting but concerns about ABS material failures caused the B149.1 to be updated forcing contractors to install venting systems using materials that meet the tougher ULC S636 standard.

New Material

While certified PVC or CPVC pipe continues to be used in most residential gas furnace and water heater installations, polypropylene material has been approved for use by several gas furnace and boiler manufacturers. The polypropylene material promises to be easier to install and less hazardous to the installer because no potentially toxic and malodorous adhesives are required. Polypropylene pipe and fittings are pushed together and then locked into place with a metal collar. The joints are leak proof and fittings can be twisted after assembly.

A corrugated, flexible polypropylene liner kit for use in masonry chimneys is also available. These options are more expensive than PVC, but are labour saving and easier to use with no odours from the cement. In my view, this may be the material of the future.

We can get the flue products to the sidewall with ease (assuming installation instructions are followed) but what happens outside can still be an adventure in the unknown zone. Codes and manufacturer instructions dictate where the pipes must terminate but too many times the rules are wildly interpreted in many cases and ignored in others.

The Faux Chimney – Category IV Vertical Vent

I suggest we get vertical – again. Horizontal terminations can create a variety of hazards to humans and to property, not to mention they are ugly, inefficient and troublesome. Plus, the open pipes can be a target for vandals or little children who seem to relish in hiding toys, stones and anything else handy in the pipe. Installing debris screens in the pipe sometimes can create problems with ice accumulation over the screen leading to blockage.

What is left but to provide a superior sidewall termination or, even better in my view, above the roofline termination? Sidewall termination kits would have to be well insulated, decorative, and move the termination point well above grade or the “highest anticipated snow level” in any location in Canada. Only an insulated vertical chase or sidewall termination kit should be used to be sure the products of combustion are safely removed from the building.

There you have it vent pipe manufacturers: How about producing an insulated, decorative, easily installed, low pressure drop, maintenance free, ULC S636 certified termination kit with offsets that all appliance manufacturers could easily certify too? And builders, how about providing an insulated chase for vent pipes terminating above the roof line in an architecturally designed, no maintenance, decorative faux chimney that prevents ice accumulation? This could be a tall order, but I think manufacturers and builders are up to it. <>

Ian McTeer is a field service representative with Ingersoll Rand HVAC. He can be reached at imcteer@irco.com.




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