How much does it cost to run an electric heater?

Hint: It's a lot more than you think!

Dear Mike (aka J.A.M.),

We had our RV sitting in the driveway over the winter and ran a space heater during the really cold months so we didn’t have to totally winterize it. But I just looked at our home electric bill for those months, and YIKES it went up a lot. So just how much does is cost to run a portable electric space heater and how does the power company calculate it? – Wanda K. 

Dear Wanda,

Great question, so it’s time to bust out a little arithmetic. Now don’t worry as it’s really simple, just multiplication.

First, every appliance is rated for the amount of wattage it draws from the power line. So a 100-watt light bulb draws 100 watts, a 1,200-watt space heater draws 1,200 watts, and a 1,800-watt hair dryer draws 1,800 watts. Seems obvious, doesn’t it? For one of my expanded articles on the typical wattage draw of appliances, click HERE.

Now, the power company doesn’t charge you by watts, they charge you by something called kilowatts, which is simply thousands of watts (or kW for short). So a 100-watt bulb uses 0.1 kW of power, a 1,200-watt heater uses 1.2 kW of power, and an 1,800-watt hair dryer uses 1.8 kW of power. With me so far?

Watts times hours equals energy!

That power usage is what we see as a spinning dial in an old-school electric meter. So it should be obvious that if you run an appliance 10 times longer than you did last month, the dial is going to spin 10 times as many revolutions, and the power company is going to charge you 10 times as much.

And indeed they do. The Power Company not only charges yoy by kW (kilowatts) of power (how fast the dial spins), but also by how many hours you use it (the total number of revolutions). What they’re actually metering is something called kilowatt hours (commonly abbreviated as kWh) of energy. You should find a notification on your monthly electric bill for a kWh rate, which let’s assume is 10 cents, or 0.10 dollars per kWh. So more hours you run a space heater, the more energy the power company is going to charge you.

Here comes the arithmetic….

Now we’ll put it all together and see what a space heater could cost to run. Let’s assume it’s a 1,200-watt heater, so that’s 1.2 kW of power. And let’s assume it runs 50% of the time to keep your RV up to the desired temperature (that’s what we call a 50% duty cycle). Since there’s 24 hours in the day, that’s 12 hours of actual running time per day. And if you multiply 12 hours (of running time) times 1.2 kW (1,200 watts) you come up with 14.4 kilowatt hours (kWh)of energy per day.

If we then multiply 14.4 kWh per day times 30 days in a month, that works out to 432 kWh of electrical energy usage per month. Now all we have to do is multiply 432 kWh times the 0.10 dollars per kWh the power company is charging you. That’s 14.4 kWh x 30 days x 0.10 dollars per kWh equals $43.20. So running a single 1,200-watt space heater that’s on 50% of the time could add around $43 per month to your electric bill. And two space heaters could be $86 per month. Yikes!

Here’s the math in a simple string. Multiple the kW of the appliance times the percentage of time it’s on per day, times the hours in a day, times the days in the month, times the kWh rate charge. Of course, since there’s 720 hours in a 30-day month (24 x 30 = 720), you can simplify this as 1.2 (kilowatts of power usage) x .50 (50% duty cycle) x 720 (hours in the month) x 0.10 (dollars per kWh), which is 1.2 x .50 x 720 x 0.10 = $43.20

So a single 1,200-watt electric space heater in your RV or basement can easily add $43 (each) to your monthly electric bill. And that adds up quickly.

Math is your friend (not your foe)….

While this appears to be a lot of arithmatic, mathematics is really a wonderful tool to help us figure out our daily lives, not just some abstract science to determine how fast the universe is expanding (although it’s really great for that kind of thing as well). And I admit to hating math in grade school until I started taking high school physics and collage engineering classes. Then I began to see everything around me as a bunch of equations to be solved.

Pencils down, as that’s enough math for today. But I hope this has helped you determine when it’s cost effective to run a space heater, or even a bunch of light bulbs. And doing basic arithmetic is great for your brain, much as doing crossword puzzles or playing Wordle is good for you. Math is indeed power.

Okay, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play (and calculate) safe out there… Mike