The EnergyStar site has a page on heat pump hot water heaters. These are a standard tank water heater but they heat the water using a heat pump. Heat pumps pull heat out of the surrounding air which is much more efficient than creating heat from electricity. The result is that heat pump water heaters are much more efficient than a standard water heater.
The annual energy costs of a heat pump hot water heater is around $220 or less. By comparison a standard hot water heater could cost you $500 or more. A heat pump water heater could save you close to $300 a year. The exact costs of either style water heater will depend on your utility rate and usage levels.
Availability later this year.
Unfortunately it looks like the Energy Star rated heat pump water heaters aren't for sale just yet. GE talks about their model they call the Hybrid Electric Heat Pump on their website and they say it will come out in November 2009.
Since the models from the EnergyStar site aren't available at retail yet I don't see any prices on them. However, found an article discussing a GE heat pump hot water heater that cites the cost will be in the $1,200 to $1,500 range. Standard 50 gallon electric hot water heaters sell for $400 to $450 range at places like Lowe's or Home Depot if you want a model with a decent warranty. So the heat pump hot water heater will run you around $750 to $1100 more than a standard model. However you could be eligible for a 30% tax credit to offset some of that cost. If you get the full credit then that will save you $360 to $500 off the cost. That would make the total difference something in the $250 to $740.
The payback period will be in the 1 to 4 year range depending on the exact annual savings, amount you pay and tax impact.
Should you get one?
At the time that I'm writing this the heat pump water heaters aren't quite out on the market, but they will be soon. When they are available, I wouldn't rush out and buy a heat pump hot water heater unless you currently need to replace your water heater. But if, or when, your water heater breaks down then upgrading to a heat pump hot water heater will be a good investment and save you a lot of money in the long run.
Image from Energystar.gov