12-03-2009, 01:22 AM
Gas water heaters have a 1 hour recovery rating of between about 40 and 150 gallons, meaning they can raise the temperature of that amount of water by 90 degrees fahrenheit in 1 hour. Water heaters typically contain around 50 gallons of water, so it would generally take much less than an hour to heat cold water to operating temperature. On vacation mode they wouldn't need to go the full 90 degrees since the water stays warm, so it probably takes even less time. So, yes it would definitely save energy and money without much inconvenience (unless you jump in the shower having forgotten to turn it back up again).