Why Does My Furnace Intake Pipe Keep Freezing?

If your furnace intake pipe freezes, it blocks fresh air from getting to your furnace. And when this happens, your furnace senses that it’s being starved of oxygen and automatically shuts down to prevent damage to the furnace components.

So what’s causing your furnace intake pipe to ice up repeatedly? 

Well, if your furnace intake pipe frequently freezes when the furnace runs, the pipe is most likely installed improperly. Some examples of bad installation include:

  • An intake pipe that is too close to the exhaust pipe
  • An intake pipe that is too close to the ground
  • Intake and exhaust pipes that are facing the same direction.
  • Intake and exhaust pipes that stick straight out of your home/roof

We’ll take a closer look at these improper intake pipe installations and offer you 2 ways to fix the problem. 

Not interested in the details and just want your furnace fixed ASAP? Contact us and we’ll send a professional over right away.

Check your intake pipe for these install mishaps

Problem 1: An intake pipe that is too close to the exhaust pipe. 

To properly heat your home, a condensing furnace relies on 2 CPVC venting pipes: 

  1. The “exhaust pipe”  that vents combustion products away from your home
  2. The “intake pipe” that draws in clean outside air for the combustion process 


But for those vents to work properly, they should be positioned far enough from each other to prevent contamination. If they are too close to each other, combustion gases from the exhaust pipe can seep into the intake pipe. 

And when those warm combustion gases come into contact with your cold intake pipe, they condense and eventually freeze. Most manufacturers recommend keeping the two pipes at least 12 inches from each other.

Problem 2: An intake pipe that is too close to the ground. 

Intake pipes should be placed above the “snow grade” (the point at which the snow is expected to reach its highest point above ground level). A general rule of thumb for northern states is to place the intake pipe at least 3 feet above the ground. Anything lower will allow snow and ice to block your intake pipe.

Problem 3: Intake and exhaust pipes that are facing the same direction. 

Your furnace intake and exhaust vent pipes should be pointed in opposite directions to prevent cross contamination (that is, exhaust fumes being drawn into the intake pipe). If exhaust fumes are drawn into your intake pipe, that warm air will cool, condense and eventually freeze.

Problem 4: Intake and exhaust pipes that stick straight out of your home/roof. 

Both vent pipes should be installed with an elbow and the intake air pipe should have an elbow positioned downward. This prevents snow from falling into the vent and freezing up.

Example of proper furnace venting design.

Note: If you don’t see these particular installation mistakes, have a professional inspect the system. The way your furnace venting pipes should be designed really depends on the manufacturer’s installation instructions.

2 solutions to prevent your intake pipe from freezing up

If your furnace intake pipe is constantly freezing up, it’s simply a matter of bad installation design. That being said there are 2 solutions:

1. Make changes to your current intake pipe design

Have a professional inspect your current furnace vent design. They can diagnose the design issue that’s causing your intake vent to freeze up. If the issue is minor, they can make changes to fix the problem (for example, they may be able to install a downward pointing elbow to your existing intake pipe).

2. Replace your venting pipes with a concentric vent kit

A concentric vent kit is an alternative venting pipe design that allows both the intake vent and the exhaust vent to fit inside one pipe housing. The kit allows for only one hole to be made in the roof or side of the house instead of two.


Because the intake vent fits inside the exhaust piping, the concentric vent kit design prevents the intake vent from freezing or drawing in dangerous exhaust gases.


Want to prevent an iced over intake vent? Ask a MN tech

Want to keep your intake pipe from freezing and shutting your furnace down? We can help.

Just contact us today and we’ll send over a professional to inspect and fix your vent piping design.

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