Is My Heat Pump Smoking or Just Letting Off a Little Steam?

A cloud of white, odorless “smoke” billowing from your outdoor heat pump on a cold, wet Louisiana day is a good sign, not a red flag.

It means your heat pump’s defrost cycle is working, and there is no need to panic.  As your heat pump defrosts, melting ice off the outdoor coil, it produces steam that can easily be mistaken for smoke.

At Precise Comfort & Climate Specialists Inc., we understand how alarming the steam may appear. We reassure homeowners in New Orleans, every year that it is a harmless byproduct of the defrost cycle.

Heat Pump Steam Versus Smoke

We also urge our customers to learn the difference between heat pump steam and smoke.

• Steam is white, wispy, and dissipates quickly. You typically see the steam for five to 15 minutes while your heat pump defrosts.
• Smoke is gray or black, thick and lingering. It smells acrid, chemical, or like burning rubber or plastic. Smoke persists and continues to emanate from the equipment until you shut the power off.

If you see dark smoke or smell a burning odor, shut off the unit’s power at the electrical panel and call our Precise Comfort & Climate Specialists Inc. experts for emergency service. The smoke may indicate an electrical short or a failing motor that poses a fire hazard.

Now that you know the difference between heat pump steam and smoke, take a moment to learn why your heating equipment needs to defrost in the winter and what happens if it doesn’t.

Why Heat Pumps Defrost in the Winter

Heat pumps work by extracting heat energy from the cold air outside and moving it into your home. The refrigerant flowing through the outdoor coil must be colder than the outside air for the heat transfer process to work. When the outdoor temperature is cold and the humidity is high, the moisture in the air condenses and freezes onto the cold outdoor coil, creating a layer of frost or ice.

The frost and ice act as an insulator, preventing the heat pump from effectively absorbing heat from the air. This insulation reduces efficiency, forcing the unit to work harder, which can eventually damage the compressor.

What Triggers Heat Pumps to Defrost

The defrost cycle’s task is to melt the frost or ice on the coil and restore the heat pump’s efficiency. A common misconception is that defrosting occurs only when the outdoor temperature drops below a certain degree. However, a combination of factors triggers the defrost cycle:

• Outdoor Temperature: The defrost mode typically activates when the outdoor temperature ranges between 32° and 45° Fahrenheit. The air below this range is usually too dry for frost to build quickly.

• Coil Temperature: Internal sensors in your heat pump monitor the temperature of the outdoor coil. If the temperature drops too low, typically below 32°, and the pressure sensors indicate airflow is restricted, the unit detects frost forming.

• Run Cycles: Some heat pumps run the defrost cycle on a preset schedule, even if frost is not present.

The U.S. Department of Energy (DOE) recommends selecting a heat pump with demand-frost control rather than one that defrosts on a schedule. Demand-frost systems use sensors to detect frost on the outdoor coil before initiating the defrost cycle. They avoid unnecessary defrosting, which saves energy.

A time- and temperature-based defrost system cycles on and off on a schedule, even if the coil does not require defrosting.

How Heat Pumps Defrost

When the outdoor humidity and temperature cause frost or ice formation, your heat pump changes from heating to cooling mode to melt ice on the outdoor coil.

First, it reverses the direction of the refrigerant flow by activating its reversing valve. This move sends hot refrigerant gas from the compressor back into the outdoor coil. The outdoor fan shuts off, and the hot gas melts the frost on the coil. When the hot surface and cold, moist outdoor air meet, they generate a cloud of steam.

When the defrost cycle ends, the reversing valve switches the unit back to the heating mode, and the outdoor fan turns on.

When Your Heat Pump’s Defrost Cycle Fails

The defrost cycle is essential to your heat pump in New Orleans. If it does not work correctly, ice will continue to accumulate on the outdoor coil, interfering with heat transfer. Watch for these red flags:

Excessive Ice: The unit is encased in ice, not just a light layer of frost.

Cold Air Indoors: When ice prevents the coil from absorbing heat, the system stops warming your home, and your backup heat will likely kick on excessively, leading to higher energy bills.

No Steam: If the temperature is 35° to 45° Fahrenheit, which is ideal for frost, but the unit runs for hours without producing steam, the defrost control board or sensors may be malfunctioning.

Protecting Your Outdoor Unit

During a fall tune-up, our Precise Comfort & Climate Specialists Inc. experts inspect the defrost control board, check the sensors, and ensure the reversing valve operates correctly, preventing defrost failures when cold winter temperatures arrive in New Orleans. We also check refrigerant levels, tighten electrical connections, test the thermostat, and lubricate moving parts.

Maintenance prevents minor operational issues from escalating into major problems that require expensive repairs. 

You can help protect your heat pump by keeping the area around the outdoor unit clear of snow drifts, fallen leaves, and debris. Restricted airflow prevents the unit from heating properly during the defrost cycle.

Clear the base pan drain holes of debris so water from the defrost cycle can escape without refreezing around the base.

Prepare Your Heat Pump for Winter

Don’t let a cloud of steam—or the lack of this defrost byproduct—stress you out this winter. Let us at Precise Comfort & Climate Specialists Inc. be your go-to for all things heat pump in New Orleans, LA. We can prevent problems by preparing your heat pump for cold temperatures. If you have questions about your system’s operation, suspect a defrost failure, or want to schedule maintenance, call us at 504-273-0522 or request service online.