Rheem Water Heating has expanded its line with the HP-40 hybrid heat pump water heater, a new 40-gallon model designed for smaller households with a lower hot-water demand. It meets ENERGY STAR requirements; certification is pending. The unit will be available in early June. The HP-40 hybrid is 10 pounds lighter and 10 inches shorter than its 50-gallon counterpart introduced last year. The new water heater qualifies for a federal tax credit as well as many state and utility rebates and incentives.