Hot-Water Circulation

Reduce the Waiting Time for Hot Water

Bird's eye view

Eliminate wait, eliminate waste

People spend a lot of time waiting for hot water. It can take minutes for hot water to make its way from the basement or mechanical room to a distant bathroom, and all that water and energy goes down the drain.

Hot water circulation systems are a way of getting hot water to the point of use with virtually no wait, saving thousands of gallons of water each year and sometimes lowering energy bills.

See below for:

Key Materials

Check valve and pump for circulating water

Depending on the manufacturer of the equipment being used, a hot water circulation system pump is installed near the water heater or under the sink of the most distant bathroom. Systems that use the cold water supply as the return leg of the loop must include a normally closed check valve under the sink between the hot and cold water supply pipes. When the pump is activated, the check valve opens, allowing water from the hot supply pipes to cross over into the cold pipe.

Design Notes

Water and energy savings depends on design and behavior

All hot water circulation systems conserve water, but to also be energy efficient, they have to be designed and used efficiently. A timed system that automatically runs on a programmed schedule can save energy only if the home's occupants have predictable water use habits. An on-demand system is not as instantaneous, but it allows for more random behavior. If the water heater is below all of the hot water taps, a continuous, gravity fed loop can eliminate the need for an electric pump, but such systems are notorious energy wasters. Keeping the points of use as close to the water heater as possible will save energy for any of these systems.

Hot water pipes should always be insulated, but this is more important in certain situations. If not wrapped with foam or fiberglass, hot water pipes will introduce some extra heat to living spaces. This may not be a problem in a heating dominated climate, but it is still an unintended use of energy. In a gravity fed recirculation system, the pipes are essentially an extension of the hot water storage tank so they should be as resistant to heat loss as the tank itself.

Builder Tips

Insulate hot water lines

All hot water supply pipes from the water heater to the farthest fixture should be insulated.


R-2 minimum insulation

The International Residential Code covers circulating hot water systems in Section N1103.4. Among the requirements: hot water piping should be insulated to at least R-2, and all circulating hot water systems with a pump shall have a readily accessible switch to turn off the pump.


Sending several gallons of water down the drain while waiting for hot water to arrive may not seem like a big deal. But over the course of a year, that can add up to more than 1,000 gallons of water for a daily shower, to say nothing of the energy that was used to get it hot.

Potable water is an increasingly scarce resource that is already in dangerously low supply in some parts of the U.S. Throwing it away doesn't make any sense.


LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. EA7 (Energy & Atmosphere) offers 2 points for on-demand hot waterSystem to quickly deliver hot water to a bathroom or kitchen when needed, without wasting the water that has been sitting in the hot-water pipes, which circulates back to the water heater. distribution systems.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. /ICC-700 Under Ch. 8--Water Efficiency: up to 6 pts. for recirc system resulting if no more than 4 cups waste (801.1).


Distant water heaters lead to waste

Hot water circulation systems use a pump to circulate hot water from the water heater to the tap, reducing the waiting time for hot water to nearly nothing.

All hot water circulation systems save water. But not all systems save energy; some systems actually result in higher energy bills.

Choose an on-demand system. There are three types of hot water circulation systems: thermosyphon systems, time and temperature systems, and on-demand systems.

On-demand systems make the most sense in a green home because hot water is pumped to the point of use only when it is needed, minimizing standby losses. They're activated manually or by a wireless remote or motion detector.

Such a system is inexpensive to add when plumbing is being roughed in, and can be affordably retrofitted to an existing plumbing system. Installed as a retrofit, on-demand systems use existing cold water lines as the return with the help of a special valve.

Time and temperature systems. Hot water is circulated automatically to anticipate demand with the help of a timer and thermostat. An override allows homeowners to activate the pump at non-scheduled times.

While time and temperature systems cut waiting time, they increase standby heat losses. Hot water lines are essentially turned into extensions of the hot water storage tank. They save water but increase net energy use.

Thermosyphon systems. These work only in a home with a tank-type water heater located below the hot water taps — for example, in a basement. A continuous piping loop is installed between the water heater and the fixtures, with a return line coming back to the heater after the farthest fixture is served.

Because the returning water is cooler than the water in the top of the water heater, a thermosyphon is established, and water circulates through the loop, 24 hours a day, without the need of a pump.

Such systems waste large amounts of energy; according to one calculation, more energy is lost in the loop than the energy required to heat the water in the first place.


Fine Homebuilding: “Hot-water Circulation Loops”

See Hot-Water Distribution Systems, Part III by Gary Klein .

Manufacturers of pumps and valves for on-demand systems include:
D'Mand Hot Water Systems, Costa Mesa, CA.
Temtrtol Delta T, Oceanside, CA .

Image Credits:

  1. Don Mannes/Fine Homebuilding
  2. Krysta Doerfler / Fine Homebuilding
Feb 7, 2011 6:42 AM ET

Edited Feb 7, 2011 6:49 AM ET.

Optimizing Hot Water Circulation
by Richard Nielsen

Can an existing hot water circulation system be optimized to minimize energy costs / resources? Yes. Most systems install a pump at the water heater and consist of a pump, thermostat and timer. Enhancing controllability offers opportunities for owners to reduce energy waste and the impact of the environment. Examples might include; allowing homeowners to choose their comfort temperature, ability to operate their system in on-demand mode vs less efficient scheduled mode and relocating thermostatic sensors nearest to last hot water load on a circulation loop.
Optimizing a pre-existing hot water circulator through greater control has obvious benefits. Anyone interested in optimizing an existring system consider incorporating a Thermal Logic Controller TLC-X1 hot water circulation optimizer recently released by TDT Inc.

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