Solutions To Cold Water Sandwich Effect

What is the cold water sandwich effect?

A cold water sandwich effect refers to the phenomenon where the water from a heater is warm for first few minutes, then there is a burst of cold water, and then the water quickly returns to being warm again. This is a common phenomenon with tankless water heaters. There is some water which remains stored in warm condition at the mouth of the faucet or other outlets, which means when someone runs the tap or the shower, he will receive some hot water instantly. However, a tankless heater takes some time to heat up the exchanger and during that time, some cold water may get through the exchanger and reach the user. This is what results in the cold water sandwich effect. This should not be too great an inconvenience if you are turning on the heater for minor use, but you may not like it too much if you are under a shower!

The phenomenon is more common to electric water heaters than it is with gas powered heaters. The reason for this is that gas reaches the operating temperature almost immediately, whereas electric heaters may take a minute or two to reach the required temperature for heating.

However, there are solutions to this situation. Installing a recirc loop which will return the cold water back to the heater through the help of flow check valves is a common solution. But on the downside, this system results in overwork of the heater. This does not only mean greater energy consumption, but the longevity of the system suffers, too. An alternative is to plug in a small 110V 5-6 gallon tank heater to the outlet and add the recirc loop from the tank to the tankless heater. This way, the heater is spared any overwork and energy consumption remains to the minimum. For a better understanding of how this system works, interested customers can download a diagram of the process from the Rinnai website, the manufacture of the second kind of heater described above.

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