#17 Rinnai. The Tankless Heating System combines a tankless water heater with a hydronic air handler to deliver on-demand heat using the same source for both domestic hot water and space heating. For optimum heat output in both applications, a priority system temporarily shuts down the air handler during periods of high hot-water demand, preventing the unit from blowing cold air. 800.621.9419. www.foreverhotwater.com.

#18 Stiebel Eltron. The Tempra Tankless on-demand Electric Water Heater eliminates the standby heat losses associated with tank systems and reduces water-heating bills by 15% to 20%, says the firm. The compact unit’s microprocessor control allows exact temperature setting from 86 degrees F to 125 degrees F through a knob and a digital display. The heater has all-copper piping and heating elements. 800.582.8423. www.stiebel-eltron-usa.com.

#20 Heat Transfer. The Phoenix solar water heater combines domestic hot-water storage with a 97-percent-efficient, gas-fired backup in one unit. In addition, the unit features side tappings in the jacket that permit auxiliary connections to a hydro-air system for space heating. Made from stainless steel, the product incorporates a dedicated solar heat exchanger. 800.323.9651. www.htproducts.com.

#21 WaterSaver Technologies. The Aqus reservoir uses water draining from bathroom sinks to flush toilets, saving about 10 to 20 gallons per day in a two-person household, says the maker. Simple to install or retrofit, the system creates no change in the normal operation of the lavatory sink and toilet, and it requires minimal annual maintenance, the firm adds. 502.550.1506. www.watersavertech.com.

#23 Southwest Windpower. With built-in controls and inverter, the Skystream 3.7 residential wind generator has a 1.8-kW capacity. It is designed for use on properties measuring at least 0.5 acre with unobstructed views and an average wind speed of 10 mph. It is 42 feet tall. 928.779.9463. www.windenergy.com.