Is my ECU hooked up right?

[tpaairman]

I have an ECU from the heat pump for the hot water heater. It was installed when the house was built, but tonight, as I was working on the water heater, I noticed something odd. Of the two lines from the ECU, the one marked hot goes to the bottom of the water heater where the drain valve is. That part makes since. However the line marked cold is connected to the hot water output of the water heater. Shouldn't that be connected to the cold water supply?

[firecontrol]

Have you asked the contractor that installed it?

[motoguy128]

I thought a heat pumps based hot water heater needs to circulate the water in and out of the tank. So the cold water is used for make-up. So no, it would not be connected to the cold water because it lask to BTU's to heat cold water up to temp on 1 pass. It can probably only raise the temp of the water on each pass maybe 20-30F (I'm taking a guess). It might have to turnover the tank 3 or 4 times to get to temp. That's why a storage tank is nessesary. Only tankless units can heat water directly. That's why many of them are 100k BTU or more. While a comparable HW heater is almost half that.

I however don't know much about heat pump based hot water heaters so I could be compeltely wrong.... but since noone else replied I though it was worth taking a guess.

[karsthuntr]

Yes it is hooked up correctly. You need to make sure the WH temp is set below ecu temp.

[beenthere]

If it was connected to the cold water pipe.
It would short cycle the water.
The cold water dip tube isn't too far above the drain valve.

[tpaairman]

Why would it short cycle the water? If it were connected to the cold side, it would not be sucking water from the tank, it would come from the supply pressure.

[beenthere]

If no water is being tapped. It has to draw water from the tank.

It can't pull water from the cold pipe, and put it in the tank, if no water is being tapped.

It circulates the water in the tank, until the water is up to temp, or the heat pump shuts off, or hot water is tapped. But, once hot water is no longer being tapped, it recirculates the water tank water to heat it up.