Log in
Glossary

Crankcase Heater

Crankcase Heater

This small electrical band wraps around the outside of your heat pump or air conditioner compressor. It keeps the internal oil warm when the weather gets cold outside. Warm oil flows easily and stops liquid refrigerant from damaging the moving parts when the system starts up.

Reviewed by Sarah JUpdated June 21, 20263 min read

Origin

The word crankcase dates back to the late 1800s and refers to the metal housing that holds a machine crankshaft. Engineers added heaters to these cases in the mid 1900s to protect outdoor mechanical equipment during winter.

How you'll see it used

  • An HVAC technician noted on the spring maintenance invoice that they installed a belly-band crankcase heater to protect the older AC unit during unseasonably cold nights.
  • The home inspector flagged a loose crankcase heater strap dangling from the outdoor heat pump, warning the buyer that the compressor could suffer damage next winter.
  • A homeowner reviewing a quote for a new central heat pump saw a 150 dollar line item for a factory-installed crankcase heater.

What a Crankcase Heater Does

Your outdoor air conditioner or heat pump has a large compressor inside it. This compressor acts like the heart of your HVAC & Climate Control system. It pumps refrigerant gas through the copper lines to cool or heat your house. Just like a car engine, this compressor needs lubricating oil to keep the moving metal parts running smoothly. When the weather gets cold, this oil gets thick and sluggish. A crankcase heater is a small electrical band or heating element that wraps around the bottom of the compressor. It turns on automatically when the temperature drops. This keeps the oil warm and fluid so your system can start up safely in cold weather.

Why It Matters for Your System

Cold weather causes a big problem for heat pumps and air conditioners. Refrigerant naturally wants to mix with the lubricating oil when the system sits idle. If the temperature gets low enough, the refrigerant turns into a liquid and settles at the bottom of the compressor. When the system kicks on, the compressor tries to pump this liquid. Compressors are built to pump gas, not liquid. Pumping liquid refrigerant can break the internal valves or wash away the protective oil. This causes heavy wear and tear. The crankcase heater prevents this by keeping the compressor warm. The heat boils the liquid refrigerant back into a gas and leaves the lubricating oil right where it belongs.

Where You Will Run Into It

You'll usually only hear about a crankcase heater if you live in a colder climate and own a heat pump. Heat pumps run all winter long, so they rely heavily on this small heater to survive the freezing temperatures. Air conditioners also have them if you run your AC when it's chilly outside. You might spot a mention of it on a home inspection report if the inspector notices the heater band is loose or broken. You might also see it listed on a quote for a new heating system. Many modern units come with this heater already installed at the factory. Older units might need a technician to add a strap-on heater around the base of the compressor.

What to Watch For and Repair Costs

A broken crankcase heater won't stop your heating system from turning on. Instead, it slowly damages the compressor over time. Watch for these common signs that your heater might be failing:

  • A loud grinding or banging noise when the outdoor unit turns on.
  • The compressor tripping the circuit breaker on cold mornings.
  • A visible loose metal band hanging off the bottom of the compressor.

If you suspect a problem, you should call a professional to check it. Replacing a broken heater is an easy job for a technician, but you shouldn't try it yourself because it involves high voltage. You can learn more about when to call an expert in our guide to DIY vs. Hiring a Pro.

Never turn off the power to your heat pump during the winter unless you absolutely have to. The crankcase heater needs a constant power supply to keep the compressor warm. If you lose power for several hours, wait at least 12 to 24 hours after the power comes back on before you run the heat pump.

If you need to replace a bad heater, expect to pay between 150 to 300 dollars for the part and the labor. Prices and ranges vary depending on your location and the brand of your system. A new heater is a tiny price to pay to protect a compressor that costs thousands of dollars to replace.

Frequently asked

Can I install a crankcase heater myself?

You should hire a professional to install or replace this part. It requires wiring directly into the high voltage electrical panel inside the outdoor unit. Making a mistake could damage your system or cause a severe shock.

How much power does a crankcase heater use?

These heaters typically use between 40 to 70 watts of electricity, which is similar to a standard light bulb. They usually have a built in thermostat so they only draw power when the outdoor temperature drops below a certain point.

Do I need a crankcase heater for my air conditioner?

You generally only need one if you run your air conditioner when it is colder than 60 degrees outside. However, heat pumps run all winter and almost always require a crankcase heater to protect the compressor from freezing temperatures.

More glossary terms

Stud Finder

Stud Finder

This is a small hand tool that locates the hidden wooden framing boards behind your finished walls. It beeps or lights up when you slide it over a board.

 Pop Up Drain

Pop Up Drain

You'll find this stopper assembly inside most bathroom sink basins. You push down on the cap to seal the bowl or pull a small rod behind the faucet to lift it up and let water drain.

 Crisper Drawer

Crisper Drawer

A clear plastic bin at the bottom of your refrigerator designed to store fresh fruits and vegetables. It has a tiny sliding vent that lets you control how much moisture stays inside.
Share this term
Link copied