Can you install a high efficiency furnace with only one pipe?

Author: Prof. Israel Cremin  |  Last update: Friday, July 25, 2025

It's perfectly acceptable to install a high-efficiency furnace with one pipe. Just flip through the pages of any high-efficiency furnace installation manual, and you'll find the answer.

What are the two pipes on a high efficiency furnace?

Two Pipes for Two Purposes

The combustion air pipe brings air into the furnace and mixes it with fuel, allowing the fuel to burn. The exhaust pipe vents combustion gases to the outdoors.

What are the rules for furnace exhaust pipes?

The intake and exhaust pipes must be configured at least 5 feet away from each other and away from your home's doors or windows. If you think your furnace pipes may be installed incorrectly, contact an HVAC professional right away as this can mean a costly furnace repair if not attended to immediately.

Why does my furnace have two exhaust pipes?

Most high-efficiency furnaces have two pipes coming out of the wall; one to bring combustion air into the furnace and the other to blow exhaust gases back out. It's important for the exhaust gas to not get sucked back into the furnace, so manufacturers will usually give several ways to do this.

Why does my furnace have 2 PVC pipes?

Direct-vent (two-pipe) system: The two-pipe system is most common in home heating applications. It provides a direct intake vent that brings outside air to the sealed combustion chamber with one pipe, while a second vent pipe provides sealed venting of exhaust gases back to the outside of your house.

Furnace venting: is a single-pipe installation on a high-efficiency furnace a problem?

How many vent pipes are required?

A general rule of thumb for a typical house with a typical plumbing layout is to have at least one vent for each drain pipe. Consider one full-size vent stack to be a coordinator for plumbing fittings, assuring smooth and efficient operation.

Can a high efficiency furnace and water heater share a vent?

This venting may either be dedicated to the water heater or can be shared with other atmospheric vent appliances, such as a furnace. The venting must be vertical or upward sloping so that the hot exhaust rises up through the venting to exit your home.

Is it better to have two exhaust pipes?

By splitting the exhaust gases between two pipes instead of one, a dual exhaust system reduces the back pressure on the engine. This allows it to breathe better, resulting in improved performance and efficiency. Each cylinder in an engine generates power by burning a mixture of air and fuel.

Does a high efficiency furnace need a fresh air intake?

With the filter, the replacement air is drawn from outside the home. A high efficiency furnace already has a fresh air intake filter built in. In this case, installing additional fresh air intake filters will help counteract the condensation and moisture created by the furnace's combustion process.

Where to vent a high efficiency furnace?

Vent Terminal Clearances

The vent must terminate at least: One foot from windows and doors. Three feet from inside wall corners. One foot above the ground or the anticipated snow level.

What is the code for furnace exhaust?

503.6.

A Type B or L gas vent shall terminate not less than 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. A Type B-W gas vent shall terminate not less than 12 feet (3658 mm) in vertical height above the bottom of the wall furnace.

Do high efficiency furnaces need a chimney?

Higher efficiency furnaces do not let out steam that is so high in temperature. A high-efficiency unit (90% and above) does not even use the chimney! They have their own plastic pipes that leave the home from the side of the house because the steam is only about 150 degrees.

How much does it cost to replace a furnace flue pipe?

Flue Pipe: You'll pay $400 to $800 to replace a flue pipe, depending on its length and ease of access.

What is the difference between one pipe and two pipe systems?

Modern homes tend to have a single-pipe system which involves one vertical large-diameter pipe (called a soil stack) running inside the property. In older more traditional homes, it involves a dual-pipe setup. Wastewater and soil water are taken separately to the public sewer system.

What are the disadvantages of the two pipe system?

Disadvantages The provision of a separate waste stack increases initial and maintenance cost. When pipes are fixed externally, the number required for the system tend to be unsightly.

What is the best pipe for heating system?

You can use copper pipes for many things. They can even be used as building materials, but they have a couple key uses in heating a home. Copper pipes are extremely effective when used as radiator pipes, due to their ability to harness the heat.

What are the disadvantages of high efficiency furnaces?

Disadvantages of high-efficiency furnaces
  • Higher purchase cost – Energy-efficient models typically have a higher price tag than standard models.
  • Compatibility issues – Newer, more efficient models may be incompatible with your existing HVAC system or infrastructure.

Why do high efficiency furnaces use PVC pipe?

As a result, high-efficiency furnaces need a special type of venting to remove this mixture since the acidic water would damage average vents. High-efficiency furnaces need PVC pipes, which are used to remove the acidic condensation and for air intake.

Do you need a new thermostat with a high efficiency furnace?

That depends entirely on the make and model furnace that you choose. Many, but not all, high-efficiency furnaces have thermostats built in. One safe assumption to make is that if you're replacing your furnace then your thermostat probably needs to be updated as well.

What are the benefits of a single exhaust system?

There are a number of benefits to a new single exhaust, such as:
  • it's lightweight.
  • lower cost when it comes to replacing or modifying.
  • increased gas velocity (the speed at which gas travels along a car exhaust pipe)
  • easier to replace — because these systems are more readily available.

Which is better, single or dual exhaust?

Because it has two departure pipes rather than one, a dual exhaust system allows burned engine exhaust emissions to leave the combustion chamber more quickly and easily. The engine's horsepower is increased as a result, making it more potent than a single tailpipe system.

Should I get an exhaust or straight pipe?

Straight pipes offer better flow than many popular performance mufflers. This can be helpful if you're trying to maximize performance and fuel mileage. However, high quality performance mufflers such as Paradox Performance Mufflers offer flow just as good -and sometimes better- than straight pipes.

Can water heater and furnace use same exhaust pipe?

Can A Furnace And Hot Water Heater Really Share A Vent? In short, yes.

How much water drains from a high efficiency furnace?

A furnace can form as much as five or six gallons of water from condensation each day. Usually, condensate pipes are set up to carry condensation outdoors through a void in an external wall through which the water can drain harmlessly into the ground.

What is the difference between direct vent and atmospheric vent?

Direct vent systems draw air from outside for combustion and vent exhaust directly outside. Atmospheric vent systems use indoor air for combustion and vent exhaust through a duct or chimney.

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