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Until recently, hot water recirculation systems were only available for new construction. Grundfos was the first company to make a hot water recirculating system for existing homes. The estimated savings for a typical installation is 16,000 gallons of water per year.

Unlike new construction, where the hot water line forms an uninterrupted loop back to the hot water heater, the Grundfos Comfort Series recirculation system for existing homes, uses the cold water pipe as the return line.

The Grundfos Comfort Series uses a bypass valve and a pump with a built-in thermostatic control and timer to control water flow and eliminate the cold water runoff at the faucet.

The pump is installed at the hot water heater, providing the proper amount of pressure and recirculating power needed to circulate the water.

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.

There is a temperature-sensitive plug in the valve ,that the water from the hot side flows around, when it travels through the valve.

When the water sitting at the faucet has cooled down to less than 98°F (lukewarm), the plug shrinks just enough to open the valve allowing water from the hot water pipe into the cold water line.

Because the water entering the cold water line is lukewarm, and the flow rate is so low, the temperature of the cold water line does not change very much.

As the water goes through the valve ( about a tenth of a gallon per minute ) and into the cold water line, it mixes with and pushes the water in the cold water supply line towards the hot water heater.

As water is released into the cold water line, hot water is pumped through the hot water line to the valve. Once the water temperature in the hot water line reaches 98°F, the valve plug swells enough to close it, preventing water from entering the cold water lines.

Proper sizing of the pump is critical for maximum performance. Select a model based on the supply pipe length, size and pump options. ( see Grundfos recirculation pump sizing chart.)

The pump includes a built-in timer. The timer allows the pump to turn on and off at user defined times during the day. The pump will only recirculate hot water during that time. For instance, if hot water is needed most in the morning, the could be set for 6am to 8am.

The recirculation pump operates ONLY at the preset clock times specified by the user AND ONLY when the temperature conditions of the thermostat are met.

If either the timer control or the thermostatic control switch is open (off), the circulator will not operate, and the water will flow as if there were no recirculation pump installed.

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.

The recirculation pump can be installed by a certified contractor in two hours. For the average home, hot water recirculation systems generally cost less than $1,000, including parts and installation.

Performance Considerations
In new construction installations, the water is always hot in the pipe. Retrofitted systems will always experience a few seconds of cool water coming out at first, as the standing water between the valve and the faucet is cleared out.

Considerations to note involve the size of the home and the plumbing layout.

If the plumbing lines run through a concrete slab, or there is considerable distance from the pump to the valve, it may be necessary to run the faucet for several moments before the temperature at the tap is hot, even with the system installed, .

In addition, if there are several bathrooms or high-use appliances (such as dishwasher or clothes washer) competing for hot water, the limited flow of the valve may not be enough to bring enough hot water where it is needed.

The solution is to install a valve at two or more faucets or fixtures in the house. With more valves, the total flow rate increases, and the temperature in the hot line stays closer to the desired temperature.

Grundfos recommends giving the pump about an hour to do its job (set the timer to turn the pump on an hour before hot water demand is the highest. The pump consumes about 25 Watts - as much energy as a low-power light bulb.

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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