Ray, the system you refer to as a "set" system is known industry wide as a "tankless" water heating system, because it DOES NOT store heated water ? no tank. They say that the tankless system is the most energy efficient because hot water is not being continuously reheated in a storage tank. The only time the tankless type uses energy is when the hot water faucet is open. These systems are in wide use around the world, but Americans have shied away from them because they do not produce high volumes of water. For example: with a tankless system you may find it difficult to maintain warm water when the clothes washer is in operation at the same time as both bathrooms are being used by you and your family. We think tankless systems are a good thing. However, we don't think that they are for everyone.