Waterbed Energy Use
The Economics of Making Your Bed
[Editor's Note: 2014 marks Home Energy magazine's 30th year in print. To celebrate, we are rerunning a selection of older articles with comments and updates of how the topic has changed—or stayed the same.]
The waterbed is one example of an appliance that uses a lot of electricity but is usually overlooked by energy auditors. Energy use of heated waterbeds can vary from 40 kWh to 250 kWh per month. This is comparable to a typical refrigerator’s 100-kWh/month use. In the case of waterbeds, however, there are several cost-effective conservation measures that can cut electricity use by at least 30%. Simple factors, such as how hot you heat your room and your bed, and how many blankets you keep on the bed, as well as the presence of insulation around the bed, can greatly affect its energy use.
The California Department of Consumer Affairs studied electricity use of waterbeds. They placed the bed in an environmental chamber and operated it under a range of conditions. Four factors determined electricity use: room temperature, bed size, bed coverings, and insulation. We summarize their findings below. (Note that these tests are for an unoccupied bed: results undoubtedly depend on the number of occupants normally present in the bed, and on their level of activity. Your mileage may vary.)
Factors Contributing to Energy Use
❶ Bed coverings
The bureau’s baseline test was a king-size bed with a quilted mattress pad, two sheets, and a fiber-filled comforter. Replacing the comforter with 2 blankets increased the energy use by 7%, and leaving the bed unmade (comforter and top sheet pulled back to expose half the bed) added 32% to the energy use. Pulling the comforter over the waterbed has a considerable impact on how much energy it uses. In New York City, for example, where electricity costs 16¢/kWh, making the bed can save $75 per year.
❷ Bed Size
Queen-size waterbeds use about 22% less energy than king-size waterbeds because they have less surface area through which heat can be lost. More energy can be saved with an even smaller volume mattress, such as the hybrid, soft-sided waterbed (this has an air- or foam-filled border which surrounds the proportionally smaller water sack). In the bureau’s study, a queen-size hybrid model used 51% less energy than a regular queen-size model.
❸ Room Temperature
Room temperature can greatly affect your heated waterbed’s energy use. The bureau’s study found that dropping the temperature of the bedroom 10° (from 70°F to 60°F) increased the electricity use 58%. This indicates that a waterbed uses significantly more energy in a cooler room. However, many people choose to heat their bed instead of their room. If the bedroom uses electric resistance heating (as does the waterbed), this works well, since the consumer is essentially relying on task heating: the location where most heat is desired—the bed—is what is being heated. If the room is heated with gas, however, each case should be studied individually. In most instances, gas heat is cheaper than electric.
Insulation reduces the heat lost through the surfaces. Bed coverings serve as insulation on the top, but other types are typically used for the sides and base (see Table 1). Tested energy savings ranged from 11% to 32%. Insulating the sides of the bed saves the most energy (per square foot of insulation), so this should be done first, but insulating the bottom saves a substantial amount, too. The bureau claims that corrugated cardboard appears to work as well or better than polystyrene or polyethylene, but it is possible that the cardboard will crush over a short lifetime and thus lose much of its insulating properties.
Comments in 2013:
Love the waterbed article! What is scary is that I remember it! I think it would be great to put it in the 30-year anniversary issue. Then, have someone write a new article about new waterbeds and/or other bed-related products that use energy, like heated mattress pads and so on. FUN!
When Home Energy (then known as Energy Auditor & Retrofitter) came out I was living on a mountain in Colorado. I lived with 18 other people in an old, leaky mansion for a year. Two of our work projects were to build a cabin in the woods and put up insulating curtains. Little did I know then that this kind of thing would become my life’s focus. Seems like yesterday.
What this retro article showed me was that we took ourselves a lot less seriously back in the ’80s. The comment about the number of occupants and their activity level was excellent—as was the idea of pets as insulation. Maybe we should try to recapture that feeling in the magazine. Can we get some corny gags in comic form, for example?
There are a surprisingly large number of measures you can use to reduce a waterbed’s energy use, and they all, predictably, work by lessening the heat flow away from the mattress.
- Keep the bed made and covered with a quilt or several blankets. The amount of energy used by an unmade (only half-covered) bed is about 30% more than a made-up bed. In the bureau’s test with king-size beds, the unmade bed used 39 kWh extra per month (about $3, at 8¢/kWh).
- Insulate the sides of the bed. This will save about 10–15% (approximately 15 kWh per month for the king-size bed in the baseline case).
- Insulate the bottom of the bed. This measure will save approximately 15% above just insulating the sides (about 18 kWh/month for the baseline case).
- Place a thermal reflector under your waterbed heater to reduce radiant heat loss through the bottom of the bed. The bureau’s savings were 12% (approximately 15 kWh/month).
- Keep the room warm. A ten-degree increase in room temperature can produce a remarkable drop in energy use of the bed. But remember that you’re using more energy to heat the room; each case should be examined individually.
- Buy a different waterbed. This is not a practical retrofit, but should be considered when purchasing waterbeds. For example, a queen-size mattress will use 22% less energy than a king-size one. This is because it has less surface area through which heat can be lost. Hybrid beds, with soft sides, provide more insulation and thus save about 40% over a standard model. Fiber-filled water mattresses (these have some wave-reduction properties) use slightly less energy than standard water mattresses (the bureau’s test case showed a 7% savings).
Damant. G.H., J. A. McCormack, and V. Baker, Energy Usage of Typical Waterbed Systems. California Department of Consumer Affairs, Bureau of Home Furnishings Laboratory. Report No. P-82-1. June, 1982.
- A final option is to not heat the bed at all. By placing a one-inch foam pad over the water mattress, one can avoid long nights of shivering from the cold water. However, many people feel that an unheated bed does not have the qualities that they desired a waterbed for in the first place.
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