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What is High-Efficiency Furnace Venting?

Many people swear by the heating power and energy-saving aspects of having a natural gas furnace. However, if you are new to having this system style, you may be concerned about how the byproduct is vented out and away from your home.

While standard furnaces use a vertical vent to expel gas, a high efficiency condensing furnace will use a different venting method.

High-efficiency furnace venting is used to remove the harmful gases emitted through the furnace processes without causing heat loss. These systems retain the heat in your home, cooling the air in the vents to expel acidic water and carbon dioxide away from you. 

Whether you have one of these systems or are interested in replacing your old system with one, knowing the ins and outs of high-efficiency furnace venting can help you make the best choice for your home.

You can discover why these systems are different from other furnaces and why they may help you with your heating efficiency. 

How Are High-Efficiency Furnaces Vented?

Usually, when creating a vent for a furnace, HVAC technicians will go for a metal pipe or routing the exhaust through the chimney to expel any byproducts.

However, the high-efficiency furnace two-step process to retain heat creates carbon dioxide and acidic water products requiring different expulsion methods.

Despite it being only mildly acidic, this water can quickly cause corrosion within a standard metal vent and harm your home if expelled from a chimney. 

Similarly, carbon dioxide can seep into your home if the duct is damaged or sent through the chimney. Remember, heat has been removed, so it has no propulsion to travel up and out. 

To remedy this, high-efficiency furnaces use specialized venting and drains to get rid of these. Water is dripped from the furnace to the floor from the heat condenser. 

From there, you have two catch methods. You can either have a catch basin designed especially for the acidic water or a floor drain to carry the water away. 

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High-efficiency furnace venting is constructed of PVC piping, which is routed through the sidewall.

This is where exhaust, carbon dioxide, and other elements are sent out. There will also be a PVC air intake to bring oxygen to the combustion process.

These are installed horizontally from your system and airtight to prevent combustion exhaust leakage. 

What Are the Pros and Cons of High-Efficiency Furnace Venting?

As with any decision, reviewing the pros and cons can help you make the best choice for your home.

There are many factors to consider when buying a new HVAC system of any kind, from the size you need to heat your space to how efficient the system truly is. 

If you are stumped on what choice to make for your home, pros and cons can illuminate which may suit your needs.

As always, speaking to an HVAC professional can also help you in the long run. Some questions may seem easy to answer; however, there may be technical aspects that you had not considered. 

An HVAC professional can walk you through what concerns may exist in your living space for specific systems. With that in mind, what are the pros and cons of a high-efficiency furnace venting system?


There are two sides to every story, even when it comes to high-efficiency furnace venting. Up next, we’ll investigate the pros. 

Better Heating Efficiency

It is not a misnomer: high-efficiency furnaces are more efficient at heating your home. With a standard unit, heat can be lost during the process as the system vents out. 

The vertical venting method does not separate heat from byproducts, so it is carried away once it hits the chimney or flue. 

According to PVHVAC.com, high-efficiency systems use 15% of combustion created heat to add to your home’s heating. Due to the two-exchanger method, the combustion is sent through the first exchanger to capture heat. 

Once it hits the second exchange, any remaining heat is drawn out to leave just the unwanted elements, while the heat is kept for you.

This increase in heat utilization is, of course, reflected in your energy bill! Because your system doesn’t lose any heat that has been called, it doesn’t have to run as hard to heat your home. Therefore it doesn’t draw as much energy. Combined with the fact it uses natural gas, this is a win-win.

Combustion is Sealed

What does sealed combustion mean, and why is that so great? During a furnace’s combustion process, it uses the air intake to gather air to create the ignition and feed the fire. For a standard system, that air may be taken from an unused attic space. 

On the other hand, the high-efficiency furnace draws air from the exterior and into it through a sealed pipe.

The reason this is so important is due to the production of carbon monoxide that can be created.

If your furnace is drawing air from an attic without vents, it can create an environment of carbon monoxide, which is hazardous to you and anyone within your home. With a vented attic, there is less risk of this.

However, with sealed combustion from a high-efficiency furnace, any carbon monoxide, carbon dioxide, and byproducts are vented to the outside of your home through the horizontal vents. 

This means there is an extreme decrease in the risk of being harmed throughout the heating process. You get all of the heat and none of the byproduct. 

You May Qualify for Rebates and Tax Credits

As these systems use lower amounts of energy, you may be able to contact your utility company regarding the potential of a tax credit.

Any investment you make towards using less energy and bettering your home may have this unexpected benefit. You already saved money on your bill, and now you may get a little bit of extra cash.

You must contact your utility company and tax assistant to see if you can receive this. Not all utilities may make this offer for your home or area.

On top of that, the IRS has specific home improvements they will provide credits and rebates for. Your tax assistant can review current law and see if your high-efficiency furnace venting system is one!


The advantages of high-efficiency furnace venting do make a great case for owning one. However, let’s take a look at the cons to get the full picture. 

Higher Price Tag

HVAC systems are a pricey buy out of the gate. This is no secret among homeowners, who loathe the idea of even having to consider a replacement.

It is a bit of a shock to learn that choosing a system that will increase heating efficiency may be nearly double that of a standard furnace! 

This fact alone can altogether remove this furnace from the shortlist for many homeowners.

While it has a high initial cost, this can be recuperated over time due to savings in energy utilization and improved heating.

Remember, the goal is to use less energy in the long run and keep your home cozy. This system can repay you for its use sooner than you may realize. 

Higher Installation Cost

Along with a higher price tag, if this is your first high-efficiency furnace, you may find you need a bit of venting redecoration.

This system requires PVC piping for the air intake and the exhaust vents to be routed through the sidewall. Vertical venting that pre-exists is unsuitable for the exhaust this system does create. 

On top of that, if there is no existing drainage that can be modified to catch the condensate of these systems, then you will need a drainage installation.

This can be difficult as it will require worth within your home’s environment and possibly remodeling. 

Limited Placement

When it comes to your furnace, you want to put it somewhere where you can get to it if need be, but it doesn’t need to invade your space.

Unfortunately, a high-efficiency furnace requires access to an exterior wall for its venting needs, which reduces the amount of space you can place it. 

Specific basement spaces may be unsuitable as the wall will not lead to an open-air exterior, and internal closets won’t work either.

If you do not have a room, closet, or space for this massive system to get its venting needs accommodated, you may wish to pass over this option for your home. 

How Does High-Efficiency Furnace Venting Compare to Others?

When it comes down to it, both furnaces will similarly heat your home. They ignite the gas to create heat.

The combustion produces water and carbon dioxide, which are expelled away from your home through a venting system, while heat is vented to your home. The ways they differ are in: 

With a standard natural gas furnace, gas is ignited through the use of a pilot light. There is a hot surface ignition system for a high-efficiency condensate furnace that creates the combustion through electronic means.

Pilot lights run regularly, and if they go out can cause great concern. The electric method burns more evenly and provides more safety.

The drainage and venting of a standard furnace are simple: vent everything through a vertical vent in your roof.

High-efficiency furnace venting, on the other hand, is a bit more complicated. It requires PVC pipes that go through the sidewall for the venting and additional special drainage for the water. 

Finally, a high-efficiency system has two heat exchangers, unlike a standard furnace’s one.

With a typical system, heat is created and sent through the exchanger to your home.

The high-efficiency furnace venting process is a two-step exchanger method to create, retain, and separate additional heat from the byproduct. 

Final Thoughts

Despite the need for high-efficiency furnace venting, a new furnace may be just what the doctor ordered for your home.

If your furnace is over 15 years old, doesn’t heat as well, or has been giving you trouble, it is time for a new system.

High-efficiency condensate furnaces provide you with quality heat for your home and a safer environment for everyone within it.