BCAB #1524 - Hot Water Storage Tank, Protection from Contamination, Subsection 7.6.2

January 17, 2001

BCAB #1524

Re: Hot Water Storage Tank, Protection from Contamination, Subsection 7.6.2

Project Description

The device in question is a domestic hot water storage tank. This stainless steel storage tank contains a stainless steel single wall heat exchanger pipe that is connected to a heating boiler system. The heating boiler is low pressure and serves to supply heat to the building as well as heated water for the domestic hot water heat exchanger within tank. The normal operating pressure of the heating boiler is less than 30 psi, the water pressure in the building is normally in excess of 30 psi.

Reason for Appeal

Sentence indicates connections to a potable water system shall be designed and installed so that non-potable water or substances that may render the water non-potable cannot enter the system.

Appellant's Position

The appellant contends there is little risk of contamination of the domestic water supply. For the heat transfer medium to backflow into the potable water supply to render it non-potable the following would have to occur concurrently:

  1. The stainless steel heat exchanger would have to develop a leak,
  2. The city water pressure would have to be lower than the boiler pressure, and
  3. The boiler water treatment would have to be toxic.

Building Official's Position

The Building Official considers a double wall heat exchanger with a leak path is necessary to prevent potential contamination of the potable water in the domestic hot water storage tank.

Appeal Board Decision #1524

The Code does not prescribe specific protection requirements for this type of application. While the Code does not require double wall, nor prohibit single wall heat exchangers, all installations must comply with good engineering practices as required in Sentence

The Board feels good engineering practice should include analysis of the product certification and testing information to determine suitability for the intended use. Confirmation from a Professional Engineer that the design, fabrication and installation complies with good engineering practice in accordance with Sentence is an acceptable method of determining compliance.

George Humphrey, Chair