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October 5, 2009 / Jim Fenton

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.

Mattress pad power supply

Mattress pad power supply

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.

6 Comments

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  1. Barry Leiba / Oct 5 2009 10:17 pm

    Wow!
    Imagine: If you’d turned it off for a little more than half of the year, you could have saved enough money to buy you and K each one cappuccino at Starbucks.

    [No, no, I’m sorry, I don’t mean to make fun of it; I agree with you, and I’d want to turn it off too. I just can’t help, well, putting it into perspective.]

    • Jim Fenton / Oct 5 2009 10:56 pm

      There’s nothing wrong with your math or perspective, Barry. Actually, it didn’t cost us anything the past couple of years because our photovoltaic system ran at a surplus, so no cappuccinos for us!

      I’d be happy to spend a bit more for the mattress pad if the power supply had a relay to zero the standby power. But making it the cheapest possible way is probably what maximizes their sales.

  2. Jeremy E / Oct 5 2009 11:23 pm

    Could you could get one of those cheap plug-in switches and throw it in between the wall outlet and the power supply, so that you could actually switch it off when not in use? I do that for a couple of electronics I have that use a lot of standby power.

    • Jim Fenton / Oct 6 2009 8:31 am

      Sure; if I’m unable to find a new mattress pad that has negligible standby power usage, I’ll plug it into an Insteon-controlled outlet and program my controller to turn it on at the right times of the day/year.

      My real concern is about the aggregate power usage of products like this. I have no idea how many of these mattress pads there are out there, so I can’t calculate how much power is being wasted. Making people aware of the problem, so that they choose (and drive manufacturers to design) less wasteful products is what it takes to solve the macro problem. Workarounds like external switches are helpful too.

  3. steph / Oct 6 2009 8:23 am

    The power supply for my mattress pad looks exactly like that and, yes, it’s warm even when turned off. Worse that that, the thing is not that reliable the cute little mini-jacks keep trying to disconnect and not keep the pad on. Sometimes, for no reason, it will suddenly power off. But worse, a couple of times, for no reason, it TURNED ON (i.e., heated the pad) without the ON indicator light being on. Spooky.

    Mine is also dual control, but only one half is plugged in, so some savings there. As to Jeremy’s suggestion, I like it, but I would modify it to use a switchable power strip. Many of them have a lighted switch that could be found in a dark cubby between bed and nightstand.

    THANKS for the post! I look forward to a follow-up post with a new mattress pad recommendation.

  4. Ellen / Oct 6 2009 10:56 am

    Interesting. My mattress pad has a plug that just goes straight to the wall. Of course, it’s probably 15 years old, I’m thinkin’. Basically my understanding is that ANY power supply sucks power all the time whether the unit is operating or not. And there are the mystery things. Like, my HP laptop. I power it down every night. Why is there a little blue light that stays lit even so? (Connected to a power supply.) Wasteful wasteful wasteful. As you say, it’s the cumulative drain over all the houses in the country that hurts.

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