If your home is like mine, your doorbell is electric. Why electric? Who knows. But from what I’ve been able to find with Google, electric doorbells started to become popular in the early 1900s. Back then, we probably didn’t think much about the electricity cost or environmental impact of a doorbell. Not any more.
How does an electric doorbell work? It’s pretty simple. When a visitor presses the doorbell button, the button closes a circuit sending electricity from your circuit panel to some sort of noise making device – a buzzer, a solenoid-struck chime, or perhaps an electronically generated tone or tune.
Nowadays, most doorbells run on 24 volt AC Current. This was likely done for safety reasons and it makes sense. Doorbell buttons are outside and often get wet. Should you ever have a “short” in the doorbell button, your guest won’t get electrocuted (they may be shocked if you come to the door naked however – insert rim shot here 🙂
Unfortunately, US homes are wired for 120/240 volt AC current. So to get the voltage down to 24V, when the electrician installed your doorbell, he or she also installed a transformer in your circuit panel like the one in the photo.
In the photo, you see the transformer (large silver/gray thing) and wires. On the right side of the transformer are red and white wires. Those run to my doorbell in the front hallway. From there wires run to my doorbell buttons (oddly, I have a doorbell button at my back door as well)
On the left side of the transformer are white and black wires. They are connected into my circuit panel.
If you’ve followed my writing, you know that transformers are “phantom loads” and use power all the time, whether the device they power is on or off. Furthermore, many doorbell buttons have lights behind them. Naturally lights use power too. I wanted to figure out how much power my doorbell was using. So I got out my trusty Kill-A-Watt.
In order to measure power usage with the Kill-A-Watt however, I had to disconnect the doorbell from the circuit panel and put a plug on it. Then I plugged the doorbell into the Kill-A-Watt and plugged the Kill-A-Watt into the wall.
The Kill-A-Watt did its thing and in a few seconds, I was shocked (not electrically 🙂 to learn that my doorbell transformer and button lights draw a total of three watts of power. That’s 3 watts 24 hours a day, 365 days a year.
One year is 8,760 hours. 3 watts x 8,760 hours / 1000 = 26.28 kilowatt-hours to run my doorbell. At my electricity rates that’s about $3.15. Not much right? Let me make it more interesting…
There are about 5,000 homes in Hudson, MA. Lets assume that 80% of the homes have working doorbells. 80% x 5,000 = 4,000. Let’s also assume that all the doorbells draw 3 watts (I bet the older ones draw more). 4,000 x 8,760 x 3 / 1,000 = 105,200 kilowatt hours per year – enough electricity to power 10.5 average homes for a year. Ouch.
Want scarier? As of the year 2007, the US Census estimates that Massachusetts has approximately 2,700,000 households. Again, assuming 80% have working doorbells like mine, that’s 2,160,000 doorbells using 3 watts of power. 56,764,800 kilowatt-hours or 56.7 megawatt-hours of electricity to run Massachusetts’ Doorbells. Enough to power 5,676 average homes for a year (all of Hudson’s homes in fact).
How about the nation? The US Census estimates 127,901,934 homes. Using the same 80% assumption, that’s 2,689,010,261 kilowatt hours. Enough power to run about 268,900 average homes for a year. (95% of the homes in Alaska or 100% of the homes in Wyoming).
Nationwide, each kilowatt-hour of generated electricity is responsible for about 1.34 lbs of carbon dioxide. 2,689,010,261 kilowatt-hours leads to 1,801,640 tons of carbon dioxide in our atmosphere… for doorbells, sigh.
When you next visit my home, please use your fist, shout, or use the knocker; It’s a bronze acorn in the middle of my front door. Don’t go to the backdoor, that doorbell no longer works.
And, in case you forget, there’s a sign above the doorbell button out front: