A.Joseph Stoddard responds: In the situation
you describe, you can get acceptable results without a pump.
The hot water "passive recirculation" loop is a technique I
learned from an old plumber years ago. I’ve successfully
used this technique a number of times when the bathroom is
located above the hot-water heater. By providing a return
piping run to the hot-water tank, a natural circulation (called
a thermosiphon) is created. The cooler water in the upstairs
bath sinks back towards the hot-water heater, and the hot water
from the heater rises and replaces it.
I’ve had acceptable results using 1/2-inch-diameter
copper return lines, but would caution against using a
smaller-diameter return: It might not allow enough water to
circulate through the loop.
To install a passive recirculating system:
1. Turn the power off to an electric water heater,
and close the gas supply valve to a gas water heater. Shut off
the water supply to the hot-water heater.
2. Drain the heater and the related hot-water lines,
and remove the drain cock at the bottom of the hot-water
3. Install a threaded tee stud between the tank and
the drain cock (see illustration, left). To prevent bi-metal
corrosion, the tee stud should be made from the same piping
material used to connect the drain cock to the tank. Replace
the drain cock in the end of the tee stud assembly.
4. Install a tee connection in the sink’s
hot-water supply line. This tee should be installed in the
supply line as high as possible.
5. Run the return pipe from the tee at the high point
back to the tee at the hot-water tank, and test for leaks.
Insulate as much of the supply side piping as possible, but
leave the return loop uninsulated. This will reduce standby
heat loss and also help maintain the temperature differential
that "fuels" this passive recirculation loop.
Former builder Joseph Stoddard sizes and sells heating
systems for the Bailey Co. in Elmira, N.Y.
Simple Standby Hot Water