The manufacturer has expanded its tankless hot water heaters with new gas and propane models that use highly efficient condensing technology. Offering continuous flow rates of up to 8 gallons per minute, the indoor/outdoor units operate with a .91 Energy Factor and offer 180,000 BTUs. Cost: $2,130 (indoor) and $2,080 (outdoor). A. O. Smith Water Products. 866-362-9898.