Waterbeds 

Heating waterbeds can be expensive, so keep the setting at the lowest comfortable temperature. Place a blanket over the waterbed mattress (under the bottom sheet) to help keep in the warmth. Never use an electric blanket on a waterbed.

Electric Blankets

Electric blankets use very little electricity. Set it on 'high' about 15 minutes before you go to bed, then either turn it off or set it on 'low'. If you leave it on all night, remember to turn it off in the morning.