DIYbanter - View Single Post - Demand (Tankless) Water Heater with Thermostatic Shower Control

Wayne Whitney

On 2007-03-17, wrote:

Has anyone tried thermostatic shower controls with a with tankless
(demand) water heaters to avoid temperature fluctuations? Any
comnents/ thoughts?

I haven't tried it but I have a couple thoughts. Temperature
fluctuations from a tankless heater are of two kinds: the "cold water
sandwich" from stopping and restarting the flow, and the smaller
temperature fluctuations when demand changes and the burner has to
equilibrate with the new flow rate.

A thermostatic valve isn't going to do anything for the cold water
sandwich, since there is no hot water available. As for the demand
change temperature fluctuations, they last only a seconds or two. So
the question is what is the response time of a thermostatic valve? If
the response time is smaller than a couple seconds, it should shorten
the fluctuation.

I've decided to try putting a small (2.5 gallon) electric tank in
series with my tankless heater, to see if it will average out both
kinds of temperature fluctuations. I just installed in yesterday
though, so it's too soon to tell.

Cheers, Wayne