Will Your HVAC Unit Shut Down Because of Cold Air?

While HVAC heating and cooling components are designed to control air temperature, in some cases, the temperature of the air indoors or outdoors can cause damage that could shut down the system. Most furnaces, for example, have a limited upper-temperature capacity. If outdoor temps are in the extremely low range, the unit can’t add enough heat to the house to meet thermostat settings. This may result in a furnace that runs extremely long heating cycles. Over time, overheating may accelerate damage to the heat exchanger, eventually causing the furnace to be shut down.

Cold Air Vs. Hot Furnace

More gradual damage to the furnace may occur when thermostat settings inside the house are routinely maintained below a certain minimum — often around 50 to 55 degrees. Certain high-efficiency furnaces may be vulnerable in these conditions.

  • High-efficiency condensing furnaces utilize two heat exchangers.
  • The continuous flow of excessively cold indoor air circulating back to a hot furnace through return ducts often generates condensation inside the heat exchanger’s connecting tubing.
  • The repeated presence of moisture inside heat exchanger tubing causes damaging rust and corrosion over time.

Many manufacturers of condensing furnaces recommend maintaining indoor thermostat settings above 50 degrees at all times to prevent damaging condensation caused by unusually cold indoor air, which could lead to the system being shut down.

Too Cold for Air Conditioning

Cold indoor temperatures can also affect an air conditioner and cause the system to shut down.

  • The air-conditioning process naturally causes condensation to form on the indoor evaporator coil.
  • If the AC is turned on when indoor temperatures are very low, cold indoor air circulating through the evaporator coil may drop the coil temperature and cause condensation to freeze.
  • Layers of coil icing may eventually obstruct airflow through the coil. This typically triggers an automatic system shutdown until the ice melts.

Check the air conditioner’s user’s manual for more information about minimum indoor operating temperatures to prevent icing that causes system shutdown.

For more about the relationship between cold air and HVAC system shutdowns, talk to the experts at Paitson Bros. We’ve been the community source for trusted HVAC advice since 1922.

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