In this article, I’ll provide a few examples that explain the relationship between AC ratings (in BTU) and their power usage. I’ll also show you how to measure the power usage and energy consumption of your own AC.
But before that, I’ll try to shed some light on the difference between electrical power and energy.
Understanding electricity consumption: Power vs Energy
Measurement units are very confusing at times, but these units are conventional after all, so there’s no way around them. And this is the case for electrical units too.
There are 2 main units that really matter when trying to measure electricity consumption.
- kWh: This stands for kilo-Watt-hours and is equal to 1000 Wh (Watt-hours), this is the unit for measuring electrical energy. For example, we can say that a refrigerator consumed 3 kWh (or 3000 Wh) in 2 days, or a solar panel produced 1 kWh (1000 Wh) in 5 hours.
- kW: This stands for kilo-Watts and is equal to 1000 W (Watts), this is the unit for measuring electrical power. Power is the rate at which energy is being transferred. For example, we can say that a TV uses 30 Watts when it’s on, or, a solar panel produces 100 Watts under direct sunlight.
The following formula expresses the relationship between energy and power:
Energy (in Wh or kWh) = Power (in W or kW) x Time (in hours)
For example, if a TV uses 30 Watts and is left on for 10 hours, it could be said that the TV consumed 300 Wh of energy. If the same TV is only left on for 30 minutes (0.5 hours), it could be said that it consumed 15 Wh.
If you know the wattage of a particular appliance, and you know how long it runs for, you can calculate its energy consumption over a certain period. But, what if you don’t know its wattage?
There are another 2 units that are related to power and which are also important. These units are Amps (A) and Volts (V). The following formula expresses the relationship between Wattage, Voltage, and Amperage (current):
Power (in Watts) = Amperage (in Amps) x Voltage (in Volts)
For example, consider a refrigerator, that operates at 120 Volts, 2 Amps, and has an average duty cycle of 0.33 (meaning that it runs for 8 hours every 24 hours). How much power does this refrigerator use? and how much energy does it consume per day?
The power that this refrigerator uses when its ON can be calculated as such:
Power (W) = Amperage (A) x Voltage (V)
Power (W) = 2 A x 120 V
Power (W) = 240 Watts
As mentioned above, like any refrigerator, it has a duty cycle. Given that this one runs for 8 hours every 24 hours (20 mins every hour), its energy consumption over 24 hours can be calculated as such:
Energy (Wh) = Power (W) x Time (in hours)
Energy (Wh) = Power (W) x 24 hours x Duty cycle (%)
Energy (Wh) = 240 W x 24 hours x 33%
Energy (Wh) = 240 W x 8 hours
Energy (Wh) = 1920 Wh (1.92 kWh)
Click here to read more about the energy consumption of refrigerators and how much solar power is needed to run them.
Now that we’ve established the difference between power and energy, let’s dive into the electricity requirements for RV air conditioners.
How much power does an RV air conditioner use?
The amount of power that an AC uses depends on its capacity, which is measured in BTUs (British Thermal Units). The higher the BTU rating of the AC, the more power is required to run it.
The typical BTU rating for an RV air conditioner is 13500 or 15000. Air conditioners of this capacity will typically have a running wattage of around 1300-1500 Watts, and a starting (surge) wattage of about 6000-7000 Watts.
However, Class A RVs are bigger and therefore require a higher cooling capacity. In Class A RVs, air conditioners are typically rated at 27000 BTUs and can use up to 3000 watts when running.
The following table shows some of the most common RV AC sizes and their power requirements:
|BTU Rating||Avg. Running Wattage||Starting wattage||Avg. Amperage at 115-130 V(AC)|
|7000||700 Watts||2500 – 3500 W||6 Amps|
|10000||1000 Watts||4000 – 5000 W||9 Amps|
|13500||1400 Watts||5500 – 6500 W||12 Amps|
|15000||1500 Watts||6000 – 7000 W||13 Amps|
|27000||2700 Watts||11000 – 13000 W||24 Amps|
Please note that the “starting wattage” represents the amount of power that the AC needs to start. This is a surge in power that lasts for less than a second but should be taken into consideration when sizing equipment.
How much power does your RV AC use?
If you have no idea about the amount of power that your AC uses, you can easily determine it through one of these methods:
1- Look for the specifications label:
The spec sheet of your AC contains all the information you need. Once you find it, if it doesn’t include the running wattage, look for the specified amperage and voltage.
The standard voltage in the U.S. is 115 to 130 Volts. The exact amperage of your AC will depend on its size and model.
To find the amperage, look for terms such as Full Load Amps (FLA) or Compressor Rated Load in Amps. The amperage should be close to the values provided in the table above. (11-15 Amps for 13500/15000 BTU units)
Once you find the Voltage and Amperage, you can calculate the wattage through this formula:
Power (W) = Amperage (A) x Voltage (V)
2- Use the Energy Efficiency Ratio (EER):
In the U.S., appliances usually come with an EnergyGuide label (yellow label). In the case of air conditioners, these yellow labels contain the BTU rating and an Energy Efficiency Ratio.
For example, here’s an EnergyGuide label from a 10000 BTU AC:
Now, not all AC manufacturers provide an EER value, but in case yours did, the wattage of your AC can be calculated as such:
Running Wattage (W) = BTU rating (BTU) ÷ EER
Running Wattage (W) = 10000 BTUs ÷ 11
Running Wattage (W) = 910 Watts
Nowadays, most RV ACs have an EER of around 10. If you can’t find the label, divide your AC’s BTU rating by 10 and you’ll have a pretty close estimate of its power usage.
If you don’t want to leave anything to chance, you could always go for a more precise option.
3- Use an electricity usage monitor:
Measurement tools such as the Kill-A-Watt don’t cost much and provide precise data about both power usage and energy consumption.
The following video explains how to use it:
Aside from power usage, this device comes in pretty handy when trying to determine energy consumption. Which can be very complicated to estimate with appliances such as ACs and refrigerators.
This brings us to the next section.
How much energy does an RV air conditioner use?
As mentioned above, the energy that your AC consumes depends on the power it draws when it’s running, as well as the length of the period for which it runs.
In general, the average RV air conditioner consumes 1-1.5 kWh of energy per hour depending on the outdoor temperature. For example, on a summer day, and given that it’s turned on throughout the day, an RV AC should consume around 30kWh of energy per day.
Assuming that the thermostat is set at around 70°F, the amount of energy that it consumes every hour depends mainly on how hot it is. The amount of energy that it consumes per day depends on both the temperature and how long the AC is left on.
However, even when the AC is on, it doesn’t necessarily run 100% of the time. The AC’s compressor turns ON/OFF relative to the temperature.
When the air conditioner is turned on, the compressor runs constantly until the set temperature is reached. The compressor then turns on and off in a way that maintains the set temperature.
The percentage of time for which the compressor is ON is referred to as Duty Cycle. Typically, the duty cycle of an air conditioner is 70 to 90% at a temperature of 80 to 95°F.
For example, on a hot summer day, when the outdoor temperature is above 95°F, your AC will need to run almost constantly to maintain a comfortable indoor temperature.
At night when the temperature drops and your AC has achieved the set temperature, it would only need to run for about 50-70% of the time to maintain it.
So if you leave the AC on 24/7, as a rule of thumb, it should run for 80-90% of the time. This is equivalent to 19-22 hours of every 24 hours.
As a rule of thumb, we’ll assume that the AC is only really on for 21 hours per day in these conditions. So in the daily energy consumption of the RV AC can then be calculated as such:
Daily Energy Consumption (kWh) = Running Wattage (kW) x Run Time (hours)
Daily Energy Consumption (kWh) = 1.5 kW x 21 hours
Daily Energy Consumption (kWh) = 31.5 kWh
If you don’t leave it on all the time, you can estimate its energy consumption based on its run time. However, the actual run time of the air conditioner depends on its duty cycle, which itself depends on the temperature.
As a rule of thumb, we can assume that the duty cycle is around 80% at a temperature of 90°F.
For example, this is the average energy consumption of an RV AC that is left on for 5 hours a day at a temperature of 90°F:
Energy Consumption (kWh) = Running Wattage (kW) x Run Time (hours)
Energy Consumption (kWh) = Running Wattage (kW) x 5 hours x Duty Cycle (%)
Energy Consumption (kWh) = 1.5 kW x 5 hours x 80%
Energy Consumption (kWh) = 6 kWh
Please note that these are rough estimates, the exact energy consumption of your AC might be a little higher or lower.
As mentioned above, if you’re up for an experiment, you can use a Kill-A-Watt meter to monitor the air conditioner’s energy usage over a certain period.