An Unexpected Waste of Energy
We recently moved the furniture in our bedroom, enabling me to use my trusty Kill-A-Watt to measure the energy consumption of some things that were hard to reach previously. By now we’re quite aware of what the consumption of TVs, radios, and satellite receivers is.
We got quite a surprise, however, when we measured the consumption of our electric mattress pad when turned off. Like many contemporary mattress pads, ours (labeled “Safe & Warm”) uses low voltage in response to concerns that many people have about adverse health effects of electric fields. There is a power supply that sits on the floor and provides low voltage to the heating element, and also connects to the user control (on/off switch and temperature dial). As a dual-control mattress pad, there were two controls and power supplies.
My first hint came when picking up the power supply. It had not been used for several months, yet was warm. The Kill-A-Watt told the story: 4 watts of standby power consumed while turned “off” for each side of the bed. That works out to 70 kWh per year, or a cost of $10.50 per year at 15 cents per kilowatt-hour. I’m really kicking myself for not unplugging the pad during the summer months, at least, during the 5 years or so that we had it.
Unlike the satellite receiver (which downloads program information from the satellite while on standby) and the TV (which is waiting for commands from its IR remote control when on standby), I can’t think of any justification at all for the mattress pad to be consuming 8 watts continuously.
A good clue was a small label on the power supplies: “When operating properly, this power supply remains warm.” But I expected that meant when it was operating, not when it was “off”. It’s ironic that one of the selling points of mattress pads such as this is that they allow one to save energy by turning down your home’s thermostat in the winter.
We’ll be shopping for a new mattress pad soon, and from what I have been able to tell nearly all of them seem to use about the same general design. Hopefully the design has been improved in the past few years. I’ll probably be taking the Kill-A-Watt with me to stores as we decide on a new one. I’ll add a comment below if I find one that seems particularly good.