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Venting Requirements for High-Efficiency Furnaces

If you’re in the market for a new heating system, you may wonder about the venting requirements for a high-efficiency furnace. Do you have to have a particular type of vent? How long does it need to be? In this blog post, we will answer all of your venting questions!

One Pipe Vent vs Two Pipe Vent

Most high-efficiency furnaces are either one pipe or two pipe venting systems. One pipe venting uses a single wall vent that goes through the side of your house. Two pipe venting has two vents, one that goes through the side of your house and another that goes out the roof.

As a prerequisite of installation, early types of high-efficiency furnaces required the furnace to have both the single combustion air intake and exhaust. The furnace may feature a single or two-pipe exhaust system in late versions from the 1990s to the present.

Installing a combustion air intake to the unit does not increase or harm the furnace’s efficiency when not using it, but with two pipes, the system will boost the home’s efficiency.

Venting Length Requirements

The length of the venting pipes is vital to pay attention to because if they are too short, the furnace will not be able to vent properly. The venting pipes should be at least five feet long if you use a one-pipe system and ten feet long if you use a two-pipe system.

It is crucial to ensure that the venting pipes are the correct length because if they are too short, the furnace will not be able to vent properly.

Different Types of Vents

There are three different types of vents that you can use for a high-efficiency furnace: PVC, CPVC, or metal. PVC is the most common type of vent, and it is also the cheapest. CPVC is more expensive than PVC, but it is easier to install. Metal vents are the most costly, but they last the longest.


Chlorinated Polyvinyl Chloride is a more durable variant of PVC that is also more corrosion and high temperatures resistant. It is, however, somewhat more costly. It’s more common on high-efficiency home boilers, even if PVC isn’t strong enough in certain situations. The vent pipe is frequently colour-coded for easy identification.

But, since all polymers may be produced in any hue, they aren’t the only options. Be extra cautious when it comes to particular fittings included with the furnace. The vent flange on new Payne, Bryant, or Carrier furnaces is an excellent example. It’s black but made of CPVC, meaning you can’t connect it to your venting using ABS cement.


Polyvinyl Chloride (PVC) is the most often used material currently. PVC comes in a variety of sorts and classifications, and some may not be suitable to be used as flue gas exhaust. Always double-check municipal, state, and provincial laws and regulations. For instance, Schedule 40 PVC DWV is not permitted in Canada. Only PVC accredited to a particular standard (ULC S636) for flue gas vents may be used.

PVC is less expensive than CPVC, but it is not as durable. PVC is also not as resistant to high temperatures or corrosion. It is the most common type of vent, and it is also the cheapest.


Acrylonitrile-Butadiene-Styrene (ABS) is a black plastic frequently used to vent high-efficiency furnaces. It is not as durable as PVC or CPVC, but cheaper. It is the least expensive, but it is frequently overly flexible, making it vulnerable to joint leaks and even fractures as the material expands, contracts, and softens in response to temperature changes. As a result, ABS pipe is now banned in Canada for new appliance venting.

No matter what vent you choose, ensure that it is sized correctly for your furnace. If you are unsure what size vent you need, ask a professional.

Slope Requirements

The venting pipes for a high-efficiency furnace must be sloped correctly to work properly. The venting pipes should be sloped at a minimum of one-quarter inch per foot. This slope is necessary so the water will drain properly and not build up in the venting pipes.

If the venting pipes are not sloped correctly, the water will build up in the venting pipes and could cause the furnace to malfunction.


Now that you know the venting requirements for a high-efficiency furnace, you can be sure your furnace will work properly. Make sure to follow these requirements when installing your furnace. If you have any questions, be sure to ask a professional. Furnace Repair Winnipeg offers furnace repair and installation services in Winnipeg, Manitoba. Contact us today for more information.

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