188.8.131.52 Water Heaters
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This category includes residential or small commercial water heaters. Most water heaters rest on the floor although smaller units may be wall- or shelf-mounted. Tankless water heaters are often wall-mounted.
- Typical Causes of Damage
- Seismic Mitigation Considerations
Building Code Provisions
Seismic loads for water heaters are determined using Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10) Chapter 13. The principal objective is to prevent the water heater from sliding or overturning. They may be floor mounted, wall mounted, or suspended from the level above.
- ASCE/SEI 7-10 requires anchorage design for all equipment in Seismic Design Categories D, E, and F if the equipment weighs over 400 pounds.Lighter components may be exempt if the component Importance Factor Ip = 1.0.
- Items that are exempt from the anchorage design requirements must still be positively anchored to the structure. The anchorage need not be designed or detailed on the construction documents. Exempt items must also be provided with flexible connections between the equipment and associated pipes or conduits.
Retrofit Standard Provisions
Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06) contains specific requirements retrofit of water heaters. Compliance with the anchorage provisions of the standard is required when:
- The performance level is Immediate Occupancy.
- The performance level is Life Safety in High Seismicity areas and the water heater is more than 6 feet in height, or the unit is gas-fired.
Water heaters with a capacity less than 100 gallons may be retrofitted using prescriptive approaches. Larger water heaters must meet the force provisions of the standard.
Typical Causes of Damage
- Unanchored or poorly anchored tanks may slide or overturn.
- Even if the restraint is strong enough to prevent complete overturning, if it is not rigid enough, the connections to gas and water lines may be damaged by tank movement and lead to fire or to water leakage.
Figure 220.127.116.11-2 Water damage at the Talca Hospital in the 2010 magnitude-8.8 Chile Earthquake; water leaking from tank at right. This building was closed due to nonstructural damage, dominated by water damage (Photos courtesy of Bill Holmes, Rutherford & Chekene).
Figure 18.104.22.168-3 Damaged water heater in the 2010 magnitude-6.5 Eureka Earthquake. The water heater strap pulled out from the supporting concrete wall as a result of inadequate anchorage. The tank moved sufficiently to break interconnected water lines which were rigidly connected to the tank.
- Details shown are for tanks resting on the floor adjacent to a structural wall. Where the water heater is not located adjacent to a wall, it may be necessary to construct a frame around the tank or adjacent to the tank to provide anchorage.
- Flexible connections should be provided for the gas and water lines.
- Provide noncombustible spacers between the tank and wall for older units; newer units often have insulation inside the housing as part of the assembly and do not require the additional spacers.
- Larger tanks may be floor-mounted as shown for flat bottom tanks in Section 22.214.171.124 or as pictured in Figure 126.96.36.199-5.
- See also Guidelines for Earthquake Bracing of Residential Water Heaters for additional information.