Decreased Single-Temperature Application
Storage tanks are required in conjunction with WH water heaters. The heater provides rapid heating of a small volume of water; the tank provides a storage medium with enough capacity to handle short-term loads.
Under ASME section IV part HLW rules, an ASME-compliant tank is not required when the total system volume does not exceed 120 gallons, or when the total heating capacity does not exceed 200,000 BTUH.
When properly selected and installed, these tanks can provide 80% draw without appreciable temperature decrease in a single-temperature application.