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Posted by Frank Cusack on April 10, 2007, 12:42 pm
>
>> What happens though is that after getting hot water and then
>> shutting off the tap, there is now a 6 second cold water "void" in
>> the pipes. so hot water comes out for T1 seconds, then 6 seconds of
>> cold water, then hot again.
>
> Yes, this is commonly called the "cold water sandwich".
>
>> Any ideas on how to fix this? I'd thought of having a recirc pump
>> and/or a small storage tank, but I'm not sure that either one will
>> address the problem adequately if at all.
>
> Well, I have recently put a 2.5 gallon electric tank water heater just
> after my tankless gas water heater. The effect is to spread out the
> temperature change, e.g. instead of getting cold water for 6 seconds,
> you get slightly less hot water for 30-60 seconds. Plus the heater in
> the tank helps a little, as it turns on for most of that period.
>
> A more complicated solution would be to use a house-wide tempering
> valve. E.g. set your water heaters at 140 F, and set your tempering
> valve at 130 F. Then when the output temperature of the system dips a
> little, the tempering valve should compensate.
Thanks, I think I'll try the first approach. Sounds easy to do.
-frank
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