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What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

The intake duct of your furnace allows fresh air into your home, while the exhaust vent eliminates fumes and carbon monoxide produced by heating. Given that these pipes serve different functions, you might be wondering how far apart they should be.

The distance between the furnace’s intake and exhaust should be at least 10 feet. However, the manufacturer of your furnace or local codes in your area may require different dimensions. So, before finalizing the furnace installation plans, double-check these regulations.

We will also answer other furnace-related questions to help you make informed decisions about furnace setup and get the most out of your investment in the furnace.

Furnace Intake And Exhaust Duct Positioning

What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

There are various types of furnaces that can help you keep your home at a comfortable temperature during the cold months. These furnaces require energy to heat the air that is then circulated throughout your home.

An electric furnace generates heat using electricity, whereas a fuel-powered furnace generates heat using natural gas, oil, or propane.

It’s important to note that the furnace’s energy source influences its installation—fuel-powered furnaces must be vented, whereas gas furnaces do not. This article will concentrate on fuel-powered furnaces.

Carbon monoxide is produced during the combustion process of natural gas, propane, or oil. Carbon monoxide, while clear and odorless, is extremely toxic—inhaling large amounts of the gas can be fatal.

The furnaces have intake and exhaust ducts as a safety precaution and to improve efficiency. However, sufficient clearance between the ducts is required to prevent the exhausted fumes from re-entering your home and contaminating the indoor air.

It is best to leave at least ten feet between the intake and exhaust ducts of the furnace. Furthermore, at least five feet of clearance should be provided around these pipes to ensure proper air circulation.

Please keep in mind that different manufacturers or local building codes may suggest different dimensions. Checking that before finalizing your furnace installation plans is therefore recommended.

Where Should A Furnace Exhaust Vent Be Installed?

What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

The intake pipe of the furnace should be placed below the exhaust pipe. Furthermore, the intake opening should be downward facing, whereas the exhaust pipe should be upward and outward facing. These precautions reduce the possibility of toxic fumes being drawn back into your home.

The intake and exhaust pipes can be located on the side of your house or on the roof, depending on the efficiency of the furnace.

If the intake pipe is on the side of the house, it should be at least two feet above ground. This clearance keeps the pipes above the snow line even after heavy snowfall, preventing blockage.

Because the combustion process in a standard efficiency furnace produces hot gaseous byproducts, they rise naturally. As a result, the exhaust pipe of a standard efficiency furnace should be installed on the roof.

The combustion by-products of a high-efficiency furnace, on the other hand, contain moisture and gaseous substances. The presence of moisture causes the temperature of the exhaust gases to drop. As a result, these by-products do not draft as easily.

As a result, venting the exhaust fumes through the side of the house is ideal. You can also install an inducer fan to help push the fumes through the roof.

Whatever location you choose for your exhaust vent, keep it away from vegetation and air conditioning units that can be damaged by exhaust fumes. It should also be located away from doors, windows, and any other intake vents other than the furnace intake.

In addition, ensure that you follow the manufacturer’s installation instructions regarding distance from electrical meters and gas service regulators.

What Pipes Should Be Used For Furnace Exhaust?

Whether you have a standard or high-efficiency furnace, the type of pipe you should use in your furnace installation will vary.

As previously stated, standard efficiency furnaces produce hot gaseous products. As a result, metallic pipes are ideal because they can withstand high exhaust gas temperatures. When exposed to hot fumes, PVC pipes are at risk of melting.

High-efficiency furnace exhaust is acidic. As a result, schedule 40 PVC pipes are preferable because, unlike metallic pipes, they will not corrode.

It’s also important to remember to slant the furnace’s exhaust pipe to facilitate condensate drainage. If the pipe is not sufficiently sloped, the condensate will stagnate, reducing the inner diameter of the pipe. As a result, there will be insufficient pressure to eliminate the fumes.

Typically, at least 1/4-inch per pipe foot is required for furnace installation setup. As a result, the condensate formed in the exhaust vent drains back to the furnace’s drainage system.

What Is The Maximum Number Of Elbows That A Furnace Vent Can Have?

Adding elbows to your furnace vents can assist in making tight corners, preserving the system’s efficiency and proper airflow. However, including too many elbows can have a negative impact on the furnace’s operation.

Tables with guidelines on the maximum piping length for a given number of elbows are provided by manufacturers. Frequently, it is assumed that the furnace vent should have two elbows.

How To Identify A Furnace That Isn’t Properly Venting

Because carbon monoxide can easily leak into your home if your furnace is not properly vented, this is a major safety concern. As a result, it is critical to understand how to detect venting issues in your furnace. Here are some ideas:

Water On Windows
The furnace system suffers from wear and tear. As the furnace approaches the end of its useful life, the pipes may crack due to corrosion, and pipe joints may become loose. This deterioration can cause exhaust leaks, allowing some fumes to enter your home during the venting process.

We’ve already mentioned that high-efficiency furnaces produce byproducts that contain moisture.

As a result, if exhaust fumes enter your home, you may notice condensation forming, particularly on the windows.

This problem is more prevalent in the morning because the glass surfaces of the windows are cooler than the fumes. As a result, when warm and humid air collides with the cooler glass surface, vapor condenses on the windows.

Backdrafting is the indoor leakage of combustion gases such as carbon dioxide and carbon monoxide. It can be caused by an improperly sized exhaust pipe, a change in the air pressure in the furnace system, or even a blockage in the exhaust pipe.

The rate at which exhaust fumes flow through the exhaust pipe decreases as the pipe becomes too wide. As a result, these fumes have more time to enter your home. Toxic fumes can enter the indoor air if the exhaust vent becomes clogged.

If you upgrade your furnace without changing the piping, you may encounter improperly sized exhaust pipes.

A higher-efficiency furnace, for example, extracts more heat from exhaust fumes before they enter the exhaust vent. Condensation is therefore likely if additional heat loss occurs in the exhaust pipe. This issue is expected to arise when the pipes pass through unconditioned areas.

A faulty exhaust fan can cause the pressure differential in the system to change. As a result, the furnace system’s ability to exhaust combustion fumes is compromised.

Checking For Backdrafting
There are some methods you can use to check for backdrafting. To begin, look for hot air near the furnace’s exhaust vent entrance.

You can also light a wooden stick and place it near the exhaust vent opening. If the smoke does not rise, it is likely that the exhaust fumes do not either.

Finally, a carbon monoxide detector can assist in determining whether toxic levels of this pollutant are present in your indoor air.

How To Keep Exhaust Pipes Clear Of Clogs

You can avoid obstructions by installing a vent screen to keep birds and rodents out of your exhaust pipe. To reduce the risk of interfering with airflow, buy vent screens designed specifically for furnace systems.

What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

Inspect the intake and exhaust vents outside your home on a regular basis for snow or ice buildup. Please clear any blockages as soon as possible to prevent your pipes from freezing and interfering with the operation of the furnace.


Proper spacing between the furnace intake and exhaust pipe reduces the possibility of toxic fumes entering the home. In general, a vertical clearance of at least 10 feet is required. This, however, may differ depending on the manufacturer’s recommended installation instructions and local codes.

Schedule regular furnace maintenance and tune-ups prior to the start of the heating season to ensure that your family remains warm and comfortable throughout the season. Also, keep an eye out for any signs that your furnace is not venting properly to keep your family safe.

What You Need To Know About How Far Apart Should The Intake And Exhaust Ports Of A Furnace Be

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