Tankless + Electric-under-counter-heater requires expansion tank?

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Dhoerl

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I just moved into a new house where the master bath is far away from the tankless Rinnai heater. It takes 1 min to get water to the shower and 2+ to the sinks (assuming shower off). I recently discovered that Bosch and others make small 2-4 gallon water heaters that inside the cabinet (under the sink), and only need 12 amps of power to heat their contents. I would install one of these myself is I'm quite capable of doing it.

However, I find all the new houses in my neighborhood with storage water heaters have expansion tanks installed. If I add one or more of thees small electric heaters, am I required (or would prudence dictate) adding an expansion tank near the water heater (which in NC is in the garage)?

Thanks for any pointers!

David
 

John Gayewski

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If you have a closed system then you need an expansion tank. Do you have a pressure reducing valve, backflow device, or check valve that closes your system off from the main water supply?
 

WorthFlorida

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Heating 2-4 gallons would barely expand to be of concern. I installed 50 gallon WH and it only required a 2.1 gallon expansion tank.

However, I would recommend a small tankless at the sink. A company named Chromomite. They do make 120 volt models and they are thermostatic, meaning when the output temperature is reached at it set point, usually around 104º for a lav sink, the unit shuts off. Install it on the hot side of the faucet. It will heat the cool water standing in the pipe and when the hot water from your heater reaches the unit, it will shut off. It only is powered up when water is flowing as low a .2 gallons per minute.

I installed the Bosch unit at my church since I didn't have the power needed to meet the hot water demand at a sink. If full hot water is draw it runs out quite fast.

Model CM-12L/120 should suit your needs. Installation will show it connected the cold water side. You might want to call them if the warranty is voided connecting it to the hot side.

 
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