Understanding Surge Wattage in HVAC Systems – MRCOOL

🔌 What Is Surge Wattage?

Surge wattage (also called starting wattage) is the extra burst of power that an electrical device needs for a few seconds when it first turns on.

Running (Rated) Wattage = the steady amount of power a unit uses during normal operation.
Surge (Starting) Wattage = the temporary spike in power required when a unit first starts up.

Think of it like this:

When you start your car, it needs a little extra "oomph" to get the engine going.
Same with appliances—especially ones with motors or compressors (like mini splits).

When and Why Surge Happens

Motors and compressors (like in mini splits) need a quick boost of power to overcome inertia.
The colder the outside temp, the harder the unit works—and the higher the surge might be.

Real-World Applications

Generator Use: Make sure the generator can handle both surge and running wattage.
Home Electrical Planning: Avoid overloading circuits by accounting for surge demands.

🌀 Example with the MRCOOL DIY 18k BTU Mini Split:

The system might normally run at 1,360 watts in heating mode.
But when it first kicks on, it could briefly need 2,000+ watts to start up the compressor and fan.
Once it's running, it settles back down to the lower, steady wattage.

Most MRCOOL DIY systems are designed to be energy-efficient and soft-starting, but surge wattage still exists and should be planned for—especially on 18k and higher models.

The surge wattage is typically 1.5 to 1.7 times the rated wattage when the compressor and fan motor kick on—especially in colder temps when the unit works harder.

How Long Does a Surge Last?

Typically only a few seconds, just long enough for the compressor or motor to stabilize.

🛠 Why It Matters:

If you're using a generator, inverter, or power backup, it needs to handle that surge—or the unit might trip a breaker or fail to start.
It's also good to know for wiring and circuit load planning.

Troubleshooting Tip

If a system trips a breaker or won’t start on a generator, surge wattage is a likely culprit.
Make sure the power source isn't just sized for running watts—it needs extra headroom.

⚡ Tip for Usage with Generators or Power Planning:

If someone is using a generator or managing circuits, they should account for at least 2,200 watts of surge capacity for safe operation in heating mode.