AccuServ Heating and Air Conditioning

Quality #1 Where there’s smoke, there might be bad venting

January 21, 2020

Common Venting issues:

Your furnace uses gas burners to heat the air in your home. All those toxic gases from your burners need to be properly exhausted to the outdoors.

The venting system is plastic tubing that directs the toxic gasses or “flu gases” from your furnace to the outdoors.

As vital as this system is, they are often installed with poor slopes, supporting and uncertified material.

Not only can this damage your furnace, but it can result in immediate safety risk to you and your family.

We’ll go through all the deadly sins often committed by novice installers.

Poor slope

The slope refers to the horizontal angle of the venting as it exits your home.

Due to the high-efficiency nature of furnaces, they produce a lot of condensation, water. This water needs to be properly drained out.

Horizontal venting should slope 1/4″ every foot leaning towards the furnace. This slope allows the water in the venting to slide backward into the furnace to be drained out.


Water that is allowed to remain stagnant in the venting system will narrow the inner diameter of the exhaust vent. With a smaller passageway in the vent system, the ventor motor (a type of fan) inside your furnace will not be able to generate enough pressure to exhaust the flu gases.

Think of clogging of an artery.

As a result, the furnace will trigger a safety pressure switch shutting the furnace down.

Fortunately, its problem is often detected shortly after a furnace install as the furnace won’t be able to run very long with this issue. But it can be a major inconvenience during a cold winter and when you have to take another day off work for the installers to
make the correction.

Keeping a High-Efficiency Furnace Together

Venting comes in 10 ft lengths that need to be cut into shape to assembly your venting assembly. Different joint fittings; 90 degree and 45
degree elbows, couplings, etc, connect these lengths together.

When these connections are made, a special solvent or glue must be used. Regulations require that the solvent conforms to “636 certification” specific to that type of venting. The solvent should bond all pieces of the venting system to create a complete system
and be approved by TSSA for use in Ontario.

Unfortunately, you’ll encounter novice installers using non-conforming solvent, the wrong type of 636 solvent (designed for different type
of venting) or even solvent at all!

Using the incorrect solvent can translate to improper fusing of the joints having a high potential risk of the pvc vent pipes coming apart. If in the
event the pipes disconnect, you have an immediate risk of CO poisoning or death. Despite this well-known knowledge, we continue to find
systems installed using a variation of products and solvents that are not certified for use.

This is very dangerous.


Similarly, primer is needed during colder temperatures to help solvents fuse. Without primer, you will not get proper fusion with the pipes.


This too is often a missed step during furnace installation in the winter.


When venting is cut, it flares. Due to this flaring action, it doesn’t allow the pipe to fully slide into the fitting during the assembly of the venting system.

Reaming removes this flare allowing the venting to travel the full length of the fitting and allow for secure connection.


Forcing a vent pipe in a fitting without reaming will not allow for proper adhesion and risk the venting system falling apart.

No Imitators Please

There are two major suppliers for venting that conform to 636 certification; Ipex and Royal.

They both look very similar and can only be differentiated by their brand name labeled on the venting.


Although both may be certified for use, they can not be joined in the same system. The venting system has to either all be IPEX or Royal.

The problem is that installers typically only carry one type of venting with them in their vans. If they need to add to the existing venting system, which is almost the case, they’ll use whatever is available.

Unfortunately, if they only have IPEX and the system venting is royal, they’ll often just attach the IPEX to the royal rather than go through the hassle of driving to the supplier to pick up the right stuff.

These two venting manufacturers are not factory tested to work with each other. They different composites and it’s unknown how secure the connection will be.

Novice installers often get away with this as the two types of venting look the same and many homeowners do not know any better.

The worse offense we see is when neither IPEX or Royal is used, but a bootleg brand that isn’t certified for use at all. The venting is more than likely cheaper, and the installer is trying to maximize their earnings.

Measure twice, cut once
The longer the venting run becomes, the more resistance the furnace inducer motor (fan motor) has to overcome. This resistance also applies to the more bends and turns you add to the system.

Each manufacturer has a specific vent limit for their model of furnace as well as the input rating of the furnace. For example, 50K BTU furnace you can use 2″ pipe for 50ft but for a 80k furnace you can only use 2″ for 10ft.

Once you exceed that limit, you’ll have to increase to larger pipe size diameter.

Also, different joint fittings have “equivalent length”. For example, a 2″ 90 degree elbow would have equal length of 3 ft

Measuring up the total vent run and looking up the manufacturer specs can be tedious.

That’s why it’s often overlooked and installers hope for the best that it doesn’t exceed manufacturer specifications when they put it together.

Incorrectly sizing the vent system will result in the furnace running harder to vent the flu gases leading to premature failure. In extreme cases, the furnace may not start up at all.

Before 636 PVC venting was around, there was ABS.

Acrylonitrile Butadiene Styrene (ABS) was originally used for plumbing drains. However, it gained wide spread use for venting gas appliances due to cheap costs.

Cracked venting ABS venting commonly failing at the fittings

Unfortunately, After numerous reported failures this piping has been deemed insufficient for this purpose.

By 2007, new installs must meet the new 636 standards only using certified 636 PVC certified venting with it’s higher allowable temperature rating of 149F.

Often we find contractors replacing a high efficient furnace fail to replace the ABS venting and upgrade to 636. If it was a safety risk pre2007, it poses those very same safety risk today.

Don’t leave me Hanging!
Venting needs to be supported for every 3 ft of horizontal run. All that length of venting and joints and elbow get heavy, not properly supporting it can result in a disaster.

Unfortunately, just like other bad habits, this area is no exception.

Often installer will not install enough support straps; they’re too few and far between and are over the 3 ft maximum allowance.

Other times, the incorrect strapping used. Novice installers will use J hangers. These cheaper and easier to install straps don’t’ provide adequate support. Instead, metal strapping should be used that is able to go around the vent and properly secure it.

The worse type of practice is where installers don’t support the venting at all, leaving it dangling in mid air.

Furnace venting No Venting support and venting connected with Duct Tape

The risk for that is quite obvious. Being in mechanical and laundry room people will try to hang clothes or store things hanging from the piping not understanding it’s importance or purpose. This leads to cracking, breaking or sagging, of the exhaust pipe. These issues can
result in failure to the equipment or pose an immediate risk to your safety.

Venting systems are fairly safe and the cases of failed venting resulting in harm are rare.

When installed correctly you can rest easy and rely on the venting to carry the toxic gasses produced from your furnace safely outside.

However, when corners are cut, you put yourself at risk of your venting system failing and all of it’s consequences.

Sticking with reputable companies will help protect you and your family from these dangers.

Have any more questions about the proper venting technique? Let us know below!