What Causes a Furnace to Freeze Up?

Although it may sound counter-intuitive, furnace freeze-ups happen, and they are the last thing you want when it’s cold outside. Learn more about this aspect of furnace maintenance and how to prevent it from happening to you.

What is a Furnace Freeze Up?

Combustion gases inside your furnace create condensation as they cool down. When this condensation does not drain properly, and the temperature outside falls below freezing, the moisture turns into ice. This eventually stops the drain line, and your furnace shuts down to prevent internal damage.

What Causes Furnaces to Freeze?

Today’s high-efficiency furnaces have a two-stage heating system that maximizes the extraction of heat energy from the fuel combustion process.

Combustion exhaust passes into the primary heat exchanger in these furnaces, which are also called condensing furnaces. From there, the gases move on into a secondary heat exchanger, where they cool and condense, forming moisture.

The moisture then drains out of the furnace through the condensate pipe. If the line does not fully drain and temperatures fall below 32°F, the undrained water will freeze, eventually blocking the line.

What to Do if Your Furnace Freezes Up

Unfortunately, anti-freezing measures are not always followed when installing a new high-efficiency furnace. If the line freezes, it must be thawed to restore regular furnace operation.

To safely thaw your condensate line, take one or more of the following steps:

• Pour hot water (not boiling) over the condensate line
• Hold a filled hot water bottle in place on the line
• Wrap an electric heating pad around the line
• Use a hair dryer or heat gun to direct heated air onto the line
• Warm the surrounding area by setting up a space heater a few feet away from the line
• If the ice blockage is located at the exterior discharge point, break it up carefully with a hammer and screwdriver

In the alternative, call Abe Heating and Cooling today at (720) 806-6526 for an emergency service appointment. You can rely on us for all of your furnace maintenance and repair needs.

How to Avoid Furnace Freeze

The only way to prevent a furnace freeze in freezing temperatures is to eliminate the possibility of ice blocking the condensate line. Freezing in condensate lines is usually caused by improper installation. If the condensate line sags, doesn’t have an adequate pitch, or is too long, moisture will drain more slowly and be more likely to freeze.

To avoid this happening, the following measures should be followed:

• Make sure the condensate line is sloped by at least ¼-inch per foot of pipe
• Support the condensate line between the furnace and the point of exterior discharge to make sure it maintains the intended slope
• Keep the condensate line as short as possible between the furnace and the sidewall termination location.
• Keep your exterior discharge point at least 12 inches above the highest point above ground level that snowfall typically reaches in your area.

Call Abe Heating and Cooling to schedule a service call. Our skilled technicians will inspect your system and condensate line and provide a detailed estimate of any work needed to correct issues with the installation.

Need Help with Your Frozen Furnace?

To correct known problems with your furnace and take steps to prevent it from freezing up, count on the experienced HVAC professionals of Abe Heating and Cooling. Located in Brighton, Colorado, we serve the entire Denver Metro Area.