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Note: This article concerns new construction only. If you are looking for information about installing a hot water reciculation system to an existing home, click here.

The ultimate in convenience is having hot water instantly available at sinks, appliances and bathroom faucets ... not to mention significant water (and sewer) disposal savings, retaining the 12,000 - 38,000 gallons of water a typical U.S. home wastes annually waiting for hot water. Some fast-growing counties are making the installation of hot water recirculation pumps mandatory for all new construction projects.

In the normal plumbing configuration, the hot water pipe ends at farthest faucet or fixture from the hot water heater, but when a recirculating system is installed , the hot water pipe continues until it returns to the hot water tank. There are no faucets or fixtures attached to this return line.

In addition, a circulator pump, check valve and control system are installed at the water heater. When the system calls for the water to be heated, the circulator pump turns on and moves the water through the water heater, to each faucet, shower, water appliance, etc. and back through the return water pipe. This system becomes one continuous pipe loop with available hot water when you want it.

The recirculation pump can be installed by a certified contractor in about two hours. For the average home, adding a hot water recirculation system generally adds less than $1,000 to the cost of construction.

Pump size (and price) is dermined by the length of the supply pipe, supply line volume (gallons) and pump options - see Grundfos recirculation pump sizing chart.) .

If you have a recirculation pump installed , be sure all hot water pipes are insulated and leave at least a 2-inch clearance between the hot and cold water lines.. Branches off of the main hot water supply should be kept as short as possible. Local codes may require the installation of a hot water expansion tank for secondary pressure relief on cold water supply lines with check valves. It is very important to be certain that there is no trapped air in the pipe; which can damage the pump.

With the Grundfos recirculating pump, air removal can be accomplished by removing the back plug from the pump when the system is charged with water and the pump is turned off.

The pump's slotted shaft is then rotated until the air no longer escapes. Then replace the back plug. When water is shut off and faucets are opened anywhere in the house, air can be introduced into the system. To prevent air from collecting in the return line, slope all the pipes so air will flow to the high point in the line and then put a valve there so you can release the air periodically. .

For even more savings you can also incorporate a timer and/or thermostat.

Pump and Timer Only
The timer only allows the pump to turn on at certain times. Then the pump would only recirculate the hot water during that time. If you only need hot water in the morning, for example, you could set the timer for 6am to 8am.

Pump and Thermostatic Control Only
The thermostat turns off the pump when the water in the pipes reaches a certain temperature. So once the water in the pipe is hot, the pump turns off.

The thermostatic control automatically turns the circulator off when the temperature exceeds approximately 120-125°F and back on when the temperature drops below approximately 90-100°F. The thermostat is not adjustable.

The thermostat in this system is NOT an anti-scald device.
It is used to control the valve opening only, and not the temperature of the water coming out of the faucet.

Separate thermostatic valves should be used on all faucets and shower heads.

Most three-prong wall timers should work, but Grundfos makes an excellent timer for their most popular model (#UP15-18SU). It can be set in 15-minute increments and mounts right onto the pump.

Pump, Timer and Thermostatic Control
When the timer and thermostatic controls are installed together, in series, the circulator operates ONLY at the preset clock times specified by the user AND ONLY when the temperature conditions of the thermostat are met. That is, if either the timer control or the thermostatic control switch is open (off), the circulator will not operate.

When the timer and/or thermostatic control is OFF, hot water will flow normally from the hot water heater to the opened faucet, as if a recirculation pump had not been installed.

A properly installed hot water recirculation system is extremely efficient, providing hot water on demand to the entire house.

To install the pump, you'll need the pump & flanges/unions, a swing check valve, and pipe and fittings to run the return line back to the pump. The threads on the pumps are designed to attach only to flanges or unions since there are many different sizes and types of pipe. Using flanges/unions means the same pump will fit any sized pipe. An identical replacement Grundfos pump should fit existing fittings. The ISO (isolation) flanges have a screwdriver shut-off built into them so the pump can be removed from the system without turning off the water supply.

Recirculation Pumps:
About Whole House Hot Water Systems
Installation - New Construction
Adding to an Existing Home

See Also:

Centrifugal Pumps
Recirculation Pumps
Sewage Ejector Pumps
Sump Pumps
Well Pumps

Links to Related Websites:
Water Facts
Hot Water Recirculation - FAQs
Hot Water Recirculation News and Information


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