DEPARTMENT OF THE ARMY
U.S. Army Corps of Engineers
Washington, D.C. 20314-1000
3 April 1998
Engineering and Design
DOMESTIC WATER HEATERS FOR BARRACKS
1. Purpose. This letter provides basic design guidance for the sizing of domestic water
heaters for barracks buildings.
2. Applicability. This letter applies to all HQUSACE elements and USACE Commands
having military construction and design responsibility.
3. Reference. None
4. Distribution. Approved for public release; distribution is unlimited.
5. Background. There have been questions regarding the sizing for domestic water
heaters for barracks. Designers have often used ASHRAE design criteria for motels or
dormitories with some over sizing. However the peak demand for domestic hot water in
barracks is significantly larger than motels or dormitories due to the concentrated shower
pattern of the occupants. This ETL provides a uniform approach to determine domestic
water heating requirements for barracks.
(1) As with any domestic water heating system, storage tank temperature should be
maintained at a minimum of 60C (140F) to reduce the potential for Legionella
Pneumophila (Legionnaire's Disease). Note that higher storage temperatures will result in
a lower recovery rate to satisfy the peak demand. Include a cross connection with a
mixing valve between the domestic water supply and hot water supply lines (leaving the
storage tank) to limit the temperature of water distributed to plumbing fixtures to
43C (110F). Require a strainer upstream of the thermostatic mixing valve on both the
hot and cold water connections to protect the small orifice in the mixing valve from debris
that may be in either line.
(2) If a backflow preventer is installed in the domestic water main entering a building
or in the line supplying the domestic hot water system, include provisions to accommodate
thermal expansion. In barracks this can be critical as occupants often shower at the same
time and after this peak usage event, the hot water loop will be at a relatively low