Water Heater Installation & Safety
Water heater sizing, T&P relief valves, anti-scald devices, expansion tanks, maximum temperatures, and discharge requirements.
- Size water heaters using the first-hour rating method
- Describe T&P relief valve requirements and discharge pipe rules
- Identify anti-scald device types and maximum temperature limits
- Explain when expansion tanks are required in closed systems
Lesson 1
Water Heater Sizing & First-Hour Rating
Sizing Methods
Water heater capacity for residential use is determined based on first-hour rating and fixture demand - not by a fixed gallon requirement. The first-hour rating (FHR) represents the total volume of hot water the heater can deliver during the first hour of use, starting from a fully heated tank.
The FHR accounts for:
- Tank storage capacity
- Recovery rate (how fast the heater can reheat water)
- Peak demand patterns for the household
Temperature Settings
Standard residential water heater thermostat setting is 120 degrees F. However, the stored water temperature and the delivered temperature at fixtures are regulated separately by code.
Water heater capacity is sized by first-hour rating and fixture demand - not a fixed gallon minimum. The FHR combines storage capacity with recovery rate to match peak hour demand.