loop just after the tub's filter so that it receives filtered water. The hot inlet of the exchanger is piped to the top of the storage tank (using insulated copper pipes) and the cold outlet is piped to the bottom of the tank. The pump goes on the cold line, in the right direction (pumping water from the exchanger to the tank) and you can kill two birds with one stone by using the tub filter's power line to run both aquastats and the pump!

Next, you need to position and set the aquastats:

• The first aquastat sensor measures the water temperature. Set it to switch on when the temperature drops and with a value five degrees above the setting on the tub heater. Set the differential at three degrees.
• The second aquastat goes on the tank, about a third of the way down from the top. Set it to switch on when the temperature rises and with a value five degrees above the tub temperature. Again, set the differential at three degrees.

Since you've wired everything into the filter power loop, it all activates when the filter switches on. When that happens, the first aquastat checks whether the water's already hot enough and prevents overheating; the second checks if there's enough heat in the tank to pass to the tub. Between them, they manage the heat flow to provide a luxurious dip!