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Demand Plumbing

Scope

To minimize water waste at hot water faucets:

  • Design a compact plumbing distribution system. 
  • Use a recirculation line (or hot water priming loop) and short “branches” to each hot water fixture.

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

To reduce water use and energy losses associated with hot water, homes should be designed with plumbing layouts and hot water distribution systems that reduce the amount of time it takes for hot water to get from the water heater to each plumbing fixture.  Traditional hot water distribution systems consist of a trunk and branch distribution with a relatively long and large diameter main line feeding smaller branches that flowed directly to plumbing fixtures or split to serve multiple fixtures. Even in relatively small homes of 1200 square feet, the volume to the furthest fixture can exceed 1.5 gallons and the time-to-tap can be more than 90 seconds.

One water and time saving alternative is to install a circulation loop that brings the supply portion of the loop close to each plumbing fixture or appliance. The most energy efficient way to operate the pump is to use demand – initiated controls. As shown in Figure 1, a circulating pump draws hot water through the supply portion of the loop and returns to the water heater any ambient-temperature water residing within the loop. Ideally the circulation loop should be located where it can be kept as short as possible and within 10 feet of every fixture (Acker and Klein 2006).

Demand plumbing layout example

Figure 1. A demand plumbing layout uses a recirculation pump to speed delivery of hot water to plumbing fixtures. (Image courtesy of D’MAND Kontrols® systems brought to you by ACT, Inc.)

Demand-initiated recirculation systems have been found to be more energy-efficient than other timer-or temperature-based recirculation systems, because hot water is only drawn into the recirculation loop when hot water is needed. When the user activates the pump by pushing a button or via a motion sensor located near the hot-water fixture, a sensor measures the starting (ambient) temperature of the water in the pipe. The controls allow the pump to operate until a small rise in temperature has been measured (typically 5F). The Zero Energy Ready Home (ZERH) specification also allows recirculation systems that operate based on “adaptive” scheduling, meaning that they “learn” the hot water demand profile in the home and adapt their operation to meet the occupant’s schedule.

Demand-initiated circulation systems offer builders more flexibility than other techniques for reducing hot water delays because they can be installed to accommodate the layouts in a wide variety of floor plans. Some floor plans may benefit from the installation of more than one circulation loop, each with its own pump and controls.

How to Design a Demand Plumbing Distribution System:

  1. Designate a proposed location for all hot water plumbing fixtures and appliances. Best practice design specifies that hot water fixtures be as close to the water heater as possible to minimize heat loss in pipes.
  2. Design plumbing trunks and branches to store as little water as possible by running the smallest diameter pipe allowed by code between the hot water source and each fixture.
  3. To meet EPA WaterSense criteria, calculate the stored volume between each water source and water use point and ensure that not more than 0.5 gallons of water is stored between the water source and the use point.  If the volume between each water source and water use point is more than 0.5 gallons, redesign the floor plan and plumbing layout until it is less than 0.5 gallons.  See the Compliance tab for information regarding pipe volume per length for various pipe diameters.   
  4. Record all plumbing design features on plumbing diagram (Figure 2).
  5. Install the circulation loop and branches to according to the codes outlined in the Compliance tab (including correct pipe diameter and insulation).  The minimum diameter on the supply and return portions of the loop shall not be less than ¾ inch nominal. For more information on pipe insulation, see the guide Pipes in Exterior Walls.
  6. Install all pumps, controls and sensors according to the plumbing diagram and manufacturers instructions.  Controls should shut off the pump when the correct change in temperature is measured.  Controls should also have a feature to prevent operation if the water is above 105°F. 
  7. Commission the system.  See Inspection and Verification Guidance for WaterSense Labeled New Homes for more information.

Another efficient plumbing layout method to consider is Core Plumbing.

All components of the plumbing system should be included in the plumbing layout

Figure 2. All components of the recirculation system should be included in the plumbing layout. (Image courtesy of Gary Klein and D’MAND Kontrols® systems brought to you by ACT, Inc.)

Ensuring Success

Ensure all hot water pipes are adequately insulated throughout the home.  Insulation can help save energy on water heating costs, especially in households with multiple hot water draws in a row (example: many morning showers). The 2015 IECC states that all piping ¾ inch nominal and larger shall be insulated. In addition there are certain cases where insulation is also required on smaller diameter piping.  For more information see the guide Pipes in Exterior Walls.

Wherever possible, locate both hot and cold water pipes on interior walls as an extra precaution against freezing conditions.  When water pipes must be located on the exterior wall of the home, ensure they are located toward the inside of the wall, yet still surrounded by at least 1 inch of insulation. Be aware of interior freezing conditions during long vacation periods. 

EPA WaterSense Inspection Protocol

For builders seeking certification through the U.S. Environmental Protection Agency's WaterSense program, an inspector will test all hot water delivery systems to ensure compliance with the WaterSense new home specification’s requirements using the testing protocol described in the Compliance tab.

Climate

No climate-specific information applies.

Training

Right and Wrong Images

None Available

Presentations

  1. Efficient Hot Water Distribution Part 1: What’s at Stake
    Author(s): Klein
    Organization(s): DOE
  2. Efficient Hot Water Distribution Part 2: How to Get it Right
    Author(s): Klein
    Organization(s): DOE
  3. Zero Energy Ready Home Training
    Author(s): Rashkin
    Organization(s): DOE

Videos

None Available

CAD Images

None Available

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

DOE Zero Energy Ready Home (ZERH) Program

The U.S. Department of Energy (DOE) Zero Energy Ready Home National Program Requirements includes in Exhibit 1, Mandatory Requirements, Item 4, Water Efficiency, that all homes must meet the efficient design requirements found in Section 3.3 of the EPA WaterSense® Single-Family New Home Specification. 

The EPA WaterSense Single-Family New Home Specification requires builders to minimize water wasted while waiting for hot water. More specifically:

“To minimize water wasted while waiting for hot water, the hot water distribution system shall store no more than 0.5 gallons (1.9 liters) of water in any piping/manifold between the hot water source and any hot water fixture. In the case of occupant-controlled or occupancy sensor-based recirculation systems, the 0.5 gallon (1.9 liter) storage limit shall be measured from the point where the branch feeding the fixture branches off the recirculation loop, to the fixture itself. To verify that the system stores no more than 0.5 gallons (1.9 liters), verifiers shall calculate the stored volume using the piping or tubing inside diameter and the length of the piping/tubing.

Table 1 shows the maximum pipe length allowed between the water source and the use point for various pipe sizes.

Table 1. Maximum Pipe Length for Various Pipe Sizes to meet the Allowable Volume of 0.5 Gallons between Source and Use from Any Source, for the EPA WaterSense Program:

Table courtesy of Gary Klein

The EPA document Inspection and Verification Guidance for WaterSense Labeled New Homes, and the ZERH program, requires a test to ensure that hot water waste is minimized in these certified homes. 

“To account for the additional water that must be removed from the system before hot water can be delivered, no more than 0.6 gallons (2.3 liters) of water shall be collected from the hot water fixture before hot water is delivered.”  Recirculation systems must be based on an occupant-controlled switch or an occupancy sensor. Recirculation systems that are activated based solely on a timer and/or temperature sensor do not meet this requirement. Recirculation systems which operate based on “adaptive” scheduling, meaning that they “learn” the hot water demand profile in the home and adapt their operation to meet this profile, are permitted at this time. To verify that the system meets the 0.6 gallon (2.3 liter) limit, verifiers shall first initiate operation of occupant-controlled or occupancy sensor-based recirculation systems, if present, and let such systems run for at least 40 seconds. Next, a bucket or flow measuring bag (pre-marked for 0.6 gallons) shall be placed under the hot water fixture. The hot water shall be turned on completely, a digital thermometer placed in the stream of water just where it meets the water being collected, and the starting temperature recorded. Once the water reaches the pre-marked line (approximately 24 seconds for a lavatory faucet), the water shall be turned off and the ending temperature reading at the same location recorded. The temperature must increase by 10 °F. Only the fixture with the greatest stored volume between the fixture and the hot water source (or recirculation loop) needs to be tested. 

Environmental Protection Agency (EPA) WaterSense New Home Specification

The EPA WaterSense New Home Specification states that:

To minimize water wasted while waiting for hot water, the hot water delivery system shall store no more than 0.5 gallons (1.9 liters) of water in any piping/manifold between the hot water source and any hot water fixture. To account for the additional water that must be removed from the system before hot water can be delivered, no more than 0.6 gallons (2.3 liters) of water shall be collected from the hot water fixture before hot water is delivered. Recirculation systems must be demand-initiated. Systems that are activated based solely on a timer and/or temperature sensor do not meet this requirement. 

2009 IECC

Section R 403.3.1 Mechanical system piping capable of carrying fluids above 105 °F (41 °C) or below 55 °F (13 °C) shall be insulated to a minimum of R-3. 

2012 IECC

Section R 403.3.1 Mechanical system piping capable of carrying fluids above 105 °F (41 °C) or below 55 °F (13 °C) shall be insulated to a minimum of R-3. 

2009 IRC

Follow the requirements for plumbing distribution found throughout the 2009 IRC, especially including Chapter 29, Water Supply and Distribution. 

2012 IRC

Follow the requirements for plumbing distribution found throughout the 2012 IRC, especially including Chapter 29, Water Supply and Distribution. 

2012 Uniform Plumbing Code (UPC)

Follow the requirements for plumbing diameter found in Chapter 6, Water Supply and Distribution, of the 2012 Uniform Plumbing Code.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

None Available

References and Resources*

  1. Author(s): Acker, Klein
    Organization(s): Home Energy
    Publication Date: October, 2006
    Article describing how demand plumbing systems send cold water back to the water heater until hot water arrives at the sink, shower or other fixture where it is needed.
  2. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2017

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  3. Author(s): Alliance for Water Efficiency
    Organization(s): Alliance for Water Efficiency
    Publication Date: July, 2014
    Website with information and research about residential hot water distribution systems.
  4. Author(s): EPA
    Organization(s): EPA
    Publication Date: July, 2014

    Guide designed to help builders better understand and meet the hot water delivery system criteria as specified in EPA's WaterSense New Home Specification.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Last Updated: 06/08/2017