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Measurements5min read

A Guide to HVAC Amperage, Voltage, and Watts

Warmer weather is just around the corner, and with it comes cooling season. Learn some of the basics behind amperage, watts, and volts, and how they relate to your air conditioning system and home comfort.

March 18, 2024

Amperage, voltage, and watts! Oh My! Understanding what some of these electrical terms mean can help you better understand how your air conditioner works, and how to ensure you get the right air conditioner for your home. Our focus will be on central air conditioning units and ductless mini-split HVAC systems, although the same concepts apply to window units as well.

What is Amperage, Voltage, and Watts in HVAC?

You may have heard of amps, watts, and volts when shopping for electronics or kitchen appliances, but you may not know how these terms relate to your HVAC system. Specifically, how they relate to your central air conditioning system or mini-split system.

First, let’s define amps, volts, and watts.


Amperage is the strength of electrical flow or rate of flow of a current of electricity measured in amperes, or amps (A). Amps 


Voltage is the pressure in an electrical circuit that pushes the electric current through the circuit. It is measured in volts (V). Voltage is the electrical potential of electricity passing through a circuit. The higher the number of volts, the more powerful the pressure. 

You have probably seen Caution: High Voltage signs near power lines or an electric transformer box in your yard or a neighbor’s. Those transformer boxes step down high-voltage power to low-voltage power that can be safely used in your home. 


Watts (W) and kilowatts (kW) are measures of energy consumption/power consumption. A kilowatt is 1,000 watts. Multiply volts x amps and you get watts, or wattage. Your electric company charges you for your usage of electricity based on kilowatt-hours (kWh). 

Every electrical appliance, from a floor lamp to a coffee maker to your air conditioning unit, has a power rating, telling you how much power it needs to operate. This is measured in W or kW.

How Many Watts Does an Air Conditioning System Use?

How many watts a system uses depends on the type of air conditioner.

Central Air Conditioner

In general, central air conditioners use between 15 and 45 amps based on how many tons they are, and about 240 volts. A central AC unit typically uses between 3,000 and 4,000 W, A central AC unit must be hard wired and have a dedicated circuit. 

Your central air conditioning unit has a much lower running wattage than the stated wattage on an Energy Guide. That’s because they cycle on and off throughout the day, based on the temperature and the unit. 

Heat Pump

Heat pumps provide both heating and cooling. In general, air-source heat pumps require 240 volts and a dedicated circuit. The number of amps used and the wattage used will vary greatly depending on the size of the heat pump and how often the air conditioning runs. Heat pumps can range between 20 and 50 amps depending on the size.

Ductless Mini-Split System

Most ductless mini-split systems use 230-240 volts, but some smaller capacity units only require 110/120 volts. Depending on the BTU capacity, a ductless system will need 15-45 amps. The numbers will be larger with multi-zone ductless systems. All mini-split systems require a dedicated electric circuit. Indoor units should have a surge protector. 

Calculating Energy Cost

Still with us? If you want to calculate the average energy cost of an air conditioning system, you’ll need to do a little math. Keep in mind that the resulting figures won’t be exact. Your actual energy costs will vary based on several factors including:

  • The size and energy efficiency of your cooling system
  • Where you live 
  • The size of your house
  • Insulation and airflow
  • The temperature outside
  • Your usage habits including thermostat settings

Now, with that being said, here are the formulas for calculating the cost per hour, month, and year. You’ll need to know the unit’s wattage, the number of hours the unit runs each day, and the average price of electricity in your state

Per Hour

Cost per hour = (unit wattage x average cost per kWh) / 1,000

Per Month

Cost per month = (unit wattage x hours of use per day x days of use per month x cost per kWh) / 1,000

Per Year

Cost per year = (unit wattage x hours of use per day x days of use per year x cost per kWh) / 1,000

Regular AC Maintenance Is Essential for Electrical Health

By regularly changing or cleaning your air filter and scheduling an AC before the cooling season starts, you can help your system run most efficiently. For tips on when to replace or clean your filter, read our HVAC air filter maintenance guide.

You may also want to watch out for some signs that you have an electrical issue with your cooling system. Those can include:

  • Air conditioner shuts off unexpectedly
  • AC unit trips the circuit breaker
  • Voltage compatibility issues
  • Damaged wiring

If you’re having a problem with your central air conditioning, mini-split AC, or heat pump cooling, the best solution is to call a trusted HVAC company to schedule AC repair.

Work with a Trained HVAC Professional

If all of this has your head spinning, don’t worry. A trained HVAC professional will help ensure you select the right system for your needs and that your home’s electrical system is up to the task. Whether it’s a new air conditioning installation or regular AC tune-up, working with an experienced professional is crucial. 

Contact Your Local Trane Comfort Specialist

Are you shopping for a new air conditioner? Need to schedule air conditioning repair? Whatever you need, your local Trane Comfort Specialist can help. Work with a trusted HVAC professional for all of your cooling needs. 

When you choose Trane for your heating and cooling needs, you get energy-efficient, quality equipment backed by some of the best warranties in the industry.

Browse our air conditioners.

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