You probably have a rough idea of how much it costs to run your air conditioner, based upon how much your power bill rises during the summer months. But do you actually know how much energy your AC uses?
When you purchased your AC, it likely came with a yellow EnergyGuide sticker featuring an estimate of its yearly operating cost. However, this likely doesn’t factor in the electricity used by circulation fans. Secondly, as your air conditioner ages, it will become less efficient and require more electricity to produce the same level of comfort.
Thankfully, you can determine exactly how much it costs to run your AC by simply checking your electric meter and doing a little math.
You can determine your AC’s electricity consumption by comparing your energy usage when it’s on versus when it’s off.
Our goal here is to figure out how much electricity your air conditioner uses. We’re going to accomplish this by measuring how much electricity your home uses when the AC is running, and then see how much less you use when the AC is off. The difference between these two figures will indicate your AC’s electricity consumption.
First, you need to establish a baseline by shutting off your air conditioner, and seeing how many kilowatt-hours (kWh) of electricity your home uses. Once your AC is off, go find your electric meter.
Electric meters provide an ongoing measurement of your home’s electricity consumption. Much like the odometer of your car, it doesn’t reset. So in order to figure out how much electricity you use in a given length of time, you need to take two readings and find the difference.
You’ll need to know how to take a reading from your electric meter.
If you live in Sacramento, you likely have a smart meter installed by SMUD that looks something like this:
The display will alternate through four or so readouts. The readout you want is the one that shows “020” to the left as shown above. The larger five digit number is your home’s current total electricity consumption, as measured in kWh.
If PG&E is your energy provider, you will likely have a smart meter manufactured by Landis+Gyr or GE. Visit PG&E’s “Read a SmartMeter” page for information on how to read it. If you still have an old-style analog meter, read PG&E’s guide on reading analog electricity meters.
Regardless of what type or model of meter you have, they all work more or less the same. Once you understand how to read your meter, you can begin.
All you need to do is to write down your current energy usage. Then, wait exactly one hour, and check your meter again and write down the new energy reading.
Take your new reading, and subtract your old one from it. If your first reading was 05352, and your second was 05371, then 5371 – 5352 = 19. This means your household uses 19 kWh of electricity per hour with the AC off.
Now it’s time to figure out how much electricity your air conditioner uses.
You don’t want to do this experiment when it’s cool enough for your AC to not run. Wait until the hottest part of the day, when your air conditioner is running consistently. You may want to turn down the target temperature a bit to ensure that it stays on.
Once your AC is running, take a new meter reading. Then wait one hour, and take a second reading. Subtract the first reading from the second, as before, to see how much electricity your home uses with the AC on.
Now you should have two figures: the amount of energy your home used with the AC off, and the amount of energy used with the AC running. As an example, let’s say that we used 19 kWh when the AC was off, and 22 kWh when it was on. If we subtract ‘AC off’ figure from the ‘AC on’ figure, we find that our hypothetical air conditioner uses about 3 kWh of electricity per hour.
If you wish to obtain a more accurate measurement of your AC’s energy usage, use longer intervals for your readings. For instance, take a 3 hour baseline reading, and a 3 hour ‘AC on’ reading, subtract the former from the latter, and then divide by 3 to get the hourly AC electricity usage. This is especially useful if you have a smaller AC unit that doesn’t have a very large energy draw.
Once we know how much electricity the air conditioner uses, then we can determine how much it costs to run it.
Now, you need to identify your current electricity rate. If you have SMUD, this is pretty easy, as they’ve eliminated tiered pricing. Between June 1 and September 30—when you use your AC the most—SMUD currently charges $0.1291 (about 13 cents) per kWh. Outside of this period, SMUD charges $0.1128 per kWh.
If you have PG&E, this is trickier, as you’ll need to identify whether you’re on a tiered rate plan or time-of-use plan. You may need to refer to your electricity bill to determine this. Under a tiered plan, your rate can vary according to how much electricity you use, while time-of-use plans adjust the rate according to the time of day.
As of June 2017, PG&E charges residential tiered plan customers $0.19979 per kWh for use under your daily baseline quantity, and $0.27612 for every kWh over the threshold (up to 400% of the baseline). For time-of-use rates, refer to your PG&E statement.
Once you know how much you’re charged per kWh, take that amount and multiply it by how many kWH your AC used in one hour.
If our hypothetical AC that used 3 kWh is owned by a SMUD customer, then one hour of AC usage costs about 39 cents (3 kWh x $0.1291 = $0.3873). Keep in mind, this is how much it costs to run your AC continuously for one hour. If you set your thermostat’s target temperature higher (72 or 74 degrees, rather than 68), then your AC won’t run as much. Also, ACs cycle on and off as the temperature in your home changes, and on cooler days your AC will not run as often or as long as on hot days.
But with a little creative math, you can get a rough idea of how much your AC typically costs to run. If you leave your air conditioner on for 16 hours out of the day, and observation tells you that it runs for about half that time (50% of 16 hours), then you can take your hourly consumption cost, and multiply it by the number of hours the thermostat is on and the percentage of the time the AC runs to estimate the daily cost:
$0.3873 x 16 hours x 50% (0.5) = roughly $3.10 per day, or $92.95 per 30-day month
If you live in a particularly hot area, or you keep your home at a cooler temperature, then adjust the percentage on-time accordingly. If you think it runs about 70% of the time, then:
$0.3873 x 16 hours x 70% (0.7) = roughly $4.34 per day, or $130.13 per 30-day month
If you find that your aging air conditioner is costing you more than you realized, then it might be time to upgrade to a new energy efficient air conditioner. To find out how Gilmore can help you get your cooling costs under control, give us a call at 888-868-2316, or request a phone call with our website’s convenient appointment scheduler.
