Battery back up for tankless...

[Frank DuVal]

It is a flow switch. If water flows the units turns on.

So this would work IF the flow switch is wired to control power to the water heating appliance. A flow switch internal to the unit would still rely on the unit being ON and waiting for the flow switch to close, turning on the burner solenoid. All other electronics is on all the time.

 

[hillbilly1]

So this would work IF the flow switch is wired to control power to the water heating appliance. A flow switch internal to the unit would still rely on the unit being ON and waiting for the flow switch to close, turning on the burner solenoid. All other electronics is on all the time.

It’s probably an external water flow switch that turns on the inverter, which in turn powers the water heater. There would probably be a delay in getting hot water, but would save the batteries, at least that’s the way I would design it.

 

[SureFire]

A licensed plumber installed a HUGO battery backup with flow sensor at my residence. The flow sensor has two options. A brass version and a plastic one. We opted for the brass. The flow sensor is installed in-line with the cold water supply to the water heater.

Here are the obstacles the plumber faced.

The flow sensor had male ‘garden hose’ threads. The plumber did not expect this since it is not a typical thread size for in-line plumbing installs. He used two inexpensive adapters.

The HUGO only has one simplex receptacle. However, my gas tankless water heater uses a condensate pump. The water heater instructions say the condensate pump must be able to run when the water heater is running. HUGO’s manufacturer, Safeguard Power Solutions, provided instructions on how to hardwire a duplex receptacle to the battery backup. This allowed the battery backup to operate both the tankless water heater and the condensate pump. The max wattage of the water heater is 52 and the max wattage of the condensate pump is 85. The total is well within the 350W rating of the HUGO.

This is what the homeowner/customer needs to be aware of.

When on battery backup, when you turn the hot water on, the water will flow, then it will disappear for a short period of time. Leave the hot water spigot on. The water will come back.

Per the manufacturer, the battery needs to be fully depleted every six months.