Re: tandem water heaters

Posted by John Scates on February 15, 19101 at 10:52:43:
In response to Re: tandem water heaters - supply lines
Bill: First, you need to determine if the cold water is being heated by a) hot water backflowing into the cold lines, or b) conduction/heating of the cold water pipes themselves, which then indirectly heat the cold water. You probably have a little of both, but without a full schematic of you piping system, I cannot say for sure. Potential solutions: 1. A check valve (one-way) where the cold water branches off to the heater tanks would eliminate source a) above, as you suspect. However, realize that you may be getting backflow into the cold lines as a result of water expansion as it is heated. The water in each 40 gallon tank could expand by around 1.5 gallons, and it has to have somewhere to go. If you block the cold line with a check valve, you may start tripping the relief valves on your water heater tanks. An expansion tank capable of handling the total expansion, including the boiler capacity, would provide relief. 2. A simpler solution than the check valve may be to simply add some length of pipe between the cold supply and the tanks. Remember, it does not have to be a straight-line. Would there be a problem running a length of cold water pipe up and down beside the water heaters several times so that there is enough length to isolate the tanks? This could remedy both sources a) and b) listed above. Just a thought... Maybe someone else has some thoughts too. - John Scates

Posted by John Scates on February 15, 19101 at 10:52:43:

In response to Re: tandem water heaters - supply lines

Bill:
First, you need to determine if the cold water is being heated by a) hot water backflowing into the cold lines, or b) conduction/heating of the cold water pipes themselves, which then indirectly heat the cold water. You probably have a little of both, but without a full schematic of you piping system, I cannot say for sure.

Potential solutions:
1. A check valve (one-way) where the cold water branches off to the heater tanks would eliminate source a) above, as you suspect. However, realize that you may be getting backflow into the cold lines as a result of water expansion as it is heated. The water in each 40 gallon tank could expand by around 1.5 gallons, and it has to have somewhere to go. If you block the cold line with a check valve, you may start tripping the relief valves on your water heater tanks. An expansion tank capable of handling the total expansion, including the boiler capacity, would provide relief.

2. A simpler solution than the check valve may be to simply add some length of pipe between the cold supply and the tanks. Remember, it does not have to be a straight-line. Would there be a problem running a length of cold water pipe up and down beside the water heaters several times so that there is enough length to isolate the tanks? This could remedy both sources a) and b) listed above. Just a thought...

Maybe someone else has some thoughts too.

- John Scates

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