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Demand (tankless or instantaneous) water heaters heat water directly without use of a storage tank. A gas burner or electric element heats water only when there is a demand. Note: There has been some concern expressed about using these units in areas with “hard” water (calcium-carbonate rich). Be sure to check with the manufacturer if this is a potential problem.

Source: UF/IFAS Energy Efficient Homes: Water Heaters; Wendell A. Porter, Hyun-Jeong Lee, and Kathleen C. Ruppert, 2008.

Additional Resources
UF IFAS Energy Efficient Homes: Water Heaters

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