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LEED BD+C: Multifamily Midrise | v4 - LEED v4

Efficient hot water distribution system

Possible 5 points

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Behind the Intent

Heating water uses up to one-third of residential energy, much of which is lost as the water travels through pipes. Additional energy is required to operate pumps and reheat water in continuous hot water circulation loops. And when the source of hot water is far from plumbing fixtures, significant amounts of water are wasted while the user waits for hot water to arrive.

Efficient hot water distribution systems save both energy and water by delivering hot water quickly and with minimal wasted water. This is best accomplished by locating fixtures as close as possible to water heaters. Where this is not possible or practical, demand-controlled circulation loops and, in exceptional situations, electric heat traced pipes are alternative strategies.

In all cases, all hot water pipes should be insulated for maximum efficiency. Insulated trunk lines often maintain the temperature long enough to provide consistent hot water in the system through multiple uses, such as morning showers. The 2009 IECC and other codes are now beginning to require that all hot water piping and circulation loops be insulated.

Step-by-Step Guidance

Option 1. Efficient Hot Water Distribution for Single-Family Projects

Step 1. Locate fixtures and water heater early in design process
  • Group fixtures near one another. Locate bathrooms next to or above each other and near kitchen and laundry rooms (see Further Explanation, Single-Family Options, Compact Design).
  • Locate the water heater as close to bathrooms, kitchen, and laundry as possible. The water heater can be in a basement or crawl space below stacked bathrooms or in an adjacent mechanical closet. In mixed and cold climates, the water heater should be in a conditioned or semiconditioned space.
Step 2. Select hot water distribution system
  • Compact system
    • When all hot water fixtures can be located close enough to the water heater to comply with the maximum pipe lengths in Table 1, Column A, install a compact design, with either a trunk-and-branch (Figure 1) or a manifold pipe system (Figure 2).
    • Confirm that the pipe diameters and distance from the water heater to the farthest fixture meet the rating system requirements (see Further Explanation, Example Calculation for Determining Pipe Lengths).
    • In large homes, installing multiple water heaters close to fixtures, such that all hot water lines meet the requirements of Table 1, Column A or Table 2, complies with this credit.
  • Figure 1. Compact trunk and branch system. From Kruger/Seville. Green Building, 1E. © 2013 Delmar Learning, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions

    Figure 2. Compact manifold system. From Kruger/Seville. Green Building, 1E. © 2013 Delmar Learning, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions

  • Demand circulation loop
    • When hot water fixtures cannot be located close enough to the water heater to comply with the maximum pipe lengths in Table 1, Column A, install one or more demand circulation loops (Figure 3) (see Further Explanation, Single-Family Options, Noncompact Design).
    • Figure 3. Multiple demand circulation pumps. Illustration by Terrel Broiles.

    • Demand circulation loops run from the water heater past all hot water fixtures and have a pump, operated by a switch or other controller, that draws water through the line.
    • Continuous, timer-, temperature-, and convection-operated loops are not eligible for this credit.
  • Heat trace system
    • Single-family homes may use an electric heat traced trunk line in lieu of a demand circulation loop to earn half the points available in this credit.
    • Heat trace systems can be efficient in situations where a demand circulation pump would run for more than 6 hours per day or when using condensing boilers to provide hot water.
Step 3. Design system
  • Determine pipe diameters
    • Select the smallest-diameter pipes that meet the flow requirements for all fixtures and fittings.
  • Compact system design
    • Locate the water heater as close to the fixtures as possible.
    • Multiple heaters, each located near fixture groups, may be used to reduce pipe lengths.
    • Use Table 1, Column A, to determine the maximum allowable distance between the water heater and the farthest fixture, or use Table 2 to determine the maximum allowable pipe to limit the total volume of water to 64 ounces (1.89 liter) between the water heater and the farthest fixture (see Further Explanation, Calculating Pipe Lengths).
    • Confirm that the actual installed total pipe length will meet requirements of Table 1, Column A, or that the maximum volume will meet the requirements of Table 2, regardless of the direct-line distance shown on plans.
    • Include all pipe sections from the top of the water heater to the connection at the fixture in length calculations.
    • If using a manifold system, include the pipe from the heater to the manifold, the manifold, and the individual branch line.
  • Where it is difficult or costly to locate one or two fixtures close enough to the water heater or a circulation loop to qualify for this credit, a secondary small electric tankless heater may be installed.
    • For a hot water line served by the primary water heater, select a heater that is thermostatically controlled to turn off when hot water arrives through main hot water line. The secondary heater provides supplemental heating only as required (Figure 4).
    • Alternatively, the heater can be connected to a cold water line and provide all the hot water at the fixture, eliminating the need for a dedicated hot water line. This may be a suitable solution for a distant sink or rarely used bathroom. Confirm that the selected heater will provide adequate flow and temperature rise to meet fixture requirements.
  • Figure 4. Layout with multiple water heaters. Illustration by Terrel Broiles.

  • Demand circulation loop design
    • Lay out the main hot water trunk line from the water heater such that it goes no farther from each hot water fixture than the distances listed in Table 1, Column B. Use this table to determine the maximum allowable distance from the loop to the farthest fixture based on the pipe diameter, or use Table 2 to determine the maximum allowable pipe to limit the total volume of water to 24 ounces (0.71 liter) between the loop and the farthest fixture.
    • Confirm that the actual installed total pipe length will meet requirements of Table 1, Column B, or that the maximum volume will meet the requirements of Table 2, regardless of the direct-line distance shown on plans.
    • Provide an accessible location for cutoff valves, electrical power, and disconnect for demand pump at end of loop.
    • A demand pump can be installed below the sink or near the shower at the last fixture in the line, using cold water supply as the return line, or it can be connected to a dedicated return line at any point after the last fixture in the hot water supply line.
    • When using tankless water heaters, confirm that the designed return line will provide an adequate flow rate to activate the heater.
    • Provide controllers (e.g., switches, motion sensors) at each hot water fixture group that activates the pump when hot water is required.
    • Multiple demand loops, each with a separate pump, may be used if there are multiple fixture groups in distant locations.
  • Heat trace pipe design
    • Lay out the main hot water trunk line from water heater such that it goes no farther from each hot water fixture than the distances listed in Table 1, Column B. Use this table to determine the maximum allowable distance from the loop to the farthest fixture, based on the pipe diameter, or use Table 2 to determine the maximum allowable pipe to limit the total volume of water to 24 ounces (0.71 liter) between the loop and the farthest fixture.
    • Confirm that the actual installed total pipe length will meet requirements of Table 1, Column B, or that the maximum volume will meet the requirements of Table 2, regardless of the direct-line distance shown on plans.
    • Insulation on heat traced lines is required.
Step 4. Install pipes and insulation
  • Confirm that all pipe diameters and locations meet the requirements and do not exceed the lengths in Table 1 or the volumes in Table 2.
  • Install pipe insulation.
Step 5. Verify pipe lengths or volume
  • The Green Rater must inspect the installation and confirm that it meets the requirements during the predrywall inspection or perform the volume test once all fixtures are installed (see Further Explanation, Volume Performance Test).

Option 1. Efficient Hot Water Distribution for Multifamily Midrise Projects

Step 1. Select system
  • Select individual in-unit water heaters, a single central water-heating system for the entire building, or water heaters supplying individual floors or small groups of units.
  • Every hot water fixture (except tubs without showerheads) in each individual unit must meet the rating system requirements.
  • For individual in-unit water heaters and those supplying individual floors or small groups of units, follow steps for Option 1 Single Family, above.
  • Central water-heating systems in multifamily buildings may not use continuous circulation loops to provide rapid hot water to the entire building. If the main hot water line in a multifamily building has a heat trace, use the heat traced line in place of a demand circulation loop and calculate pipe lengths and water volumes according to Table 1, Column B, or Table 2 of the rating system requirements.
  • To qualify for this credit, central water-heating systems without heat traces must use demand pumps to provide hot water to fixtures and meet the requirement for pipe distances (Table 1, Column A or B) or water volumes (Table 2) (see Further Explanation, Multifamily Midrise Options).
  • A demand pump can be installed in each unit, floor, or section, or the entire building may be served with a single large pump. Each unit must be able to control the demand pump that provides hot water when needed.
Step 2. Design system
  • Determine pipe diameters. Select the smallest-diameter pipes that meet the flow requirements of all fixtures and fittings.
  • Demand circulation loop design
    • Lay out the main hot water trunk line from water heater such that it goes no farther from each hot water fixture than the distances listed in Table 1, Column B. Use this table to determine the maximum allowable distance from the loop to the farthest fixture, based on the pipe diameter, or use Table 2 to determine the maximum allowable pipe to limit the total volume of water to 24 ounces (0.71 liter) between the loop and the farthest fixture.
    • Confirm that the actual installed total pipe length will meet requirements of Table 1, Column B, or that the maximum volume will meet the requirements of Table 2, regardless of the direct-line distance shown on plans.
    • Provide an accessible location for cutoff valves, electrical power, and disconnect for demand pump at end of loop.
    • Provide controllers (e.g., switches, motion sensors) at each fixture to activate the pump when hot water is required.
    • Multifamily buildings can use multiple demand loops each with a separate pump on each loop if there are multiple fixture groups in distant locations.
    • The circulation loop should be insulated to retain heat in pipe as long as possible. Install insulation that is as thick as the diameter of the pipe, to a maximum of 2 inches (50 mm). For example, a 3/4-inch pipe should have 3/4 inch of insulation (see Option 3).
  • Heat trace trunk design
    • If a condensing boiler is installed, or if a circulation loop would operate more than 3 hours per day, install an electric heat trace to preheat the water at the end of the hot water trunk line to maintain a maximum water temperature of 125ºF (52ºC).
    • Lay out the main hot water trunk line from water heater such that it goes no farther from each hot water fixture than the distances listed in Table 1, Column B. Use this table to determine the maximum allowable distance from the loop to the farthest fixture, based on the pipe diameter, or use Table 2 to determine the maximum allowable pipe to limit the total volume of water to 24 ounces (0.71 liter) between the loop and the farthest fixture.
    • Confirm that the actual installed total pipe length will meet requirements of Table 1, Column B, or that the maximum volume will meet the requirements of table 2, regardless of the direct-line distance shown on plans.
    • The hot water trunk line should be insulated to retain heat in pipe as long as possible. Install insulation that is as thick as the diameter of the pipe, up to a maximum of 2 inches (50 mm). For example, a 3/4-inch pipe should have 3/4 inch of insulation (see Option 3).
Step 3. Install pipes and pipe insulation
  • Confirm that all pipe diameters and locations meet the requirements and do not exceed the lengths in Table 1 or the volumes in Table 2.
Step 4. Verify pipe lengths
  • The Green Rater must inspect the installation and confirm that it meets the requirements during the predrywall inspection.
Step 5. Verify final installation
  • The Green Rater must inspect the installation at final inspection and confirm that the circulation pump meets the requirements and uses appropriate controls.

Option 2. Performance Test

Step 1. Select, design and install System
  • Follow steps 1 through 3 of Option 1 to design and install a water efficient distribution system.
Step 2. Perform test

Option 3. Pipe Insulation

Step 1. Specify pipe insulation thickness and installation requirements
  • A minimum of R-4 insulation on all hot water pipe is required.
  • For best performance, specify that pipe insulation be as thick as the pipe diameter, up to a maximum of 2 inches (50 mm).
  • Identify any impediments to complete and continuous insulation, such as where pipes pass through fire-rated walls.
Step 2. Install insulation
  • Insulation must be continuous along the entire length of pipe from the point that it exits the heater to point that it reaches the fixture. It must sealed at all seams and joints with adhesive, solvent, or tape, per the manufacturer’s instructions.
  • Pay special attention to sealing at elbows, Ts, and all joints between lengths of insulation.
  • Drill sufficiently large holes through structural members so that insulation can be installed along the entire length of pipes.
Step 3. Verify installation
  • The Green Rater must inspect the insulation and confirm that it meets the requirements at the predrywall inspection.

Single-Family Option: Compact Design

All plumbing fixtures are close to each other and the water heater (Figure 5), such that all hot water pipes meet the length requirements of Table 1, Column B, or the volume requirements of Table 2. This approach minimizes the amount of pipe and insulation required, and there is no extra expense for a pump.

Figure 5. Compact plumbing design. From Kruger/Seville. Green Building, 1E. © 2013 Delmar Learning, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions

Single-Family Option: Noncompact Design

Plumbing fixtures are located far from each other and the water heater. For a house designed this way (Figure 6), there are several options to consider:

  • Single heater with one demand pump. Install a circulation loop with a demand pump at the farthest fixture from the water heater or a demand pump at the water heater (Figure 7). Locate all fixtures within the pipe length requirements of Table 1, Column B.
  • Single heater with multiple pumps. Locate the water heater in the middle of the house, close to the kitchen, and install two circulation loops, one to the shared bathroom and one to the master bathroom (Figure 8). Locate all fixtures within the pipe length requirements of Table 1, Column B.
  • Multiple heaters with no pumps. Locate one water heater near the shared bathroom and one between the master bathroom and the kitchen (Figure 9). Confirm that all pipe lengths meet the length requirements of Table 1, Column A, or the volume requirements of Table 2.

Figure 6. Noncompact plumbing design. From Kruger/Seville. Green Building, 1E. © 2013 Delmar Learning, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions

Figure 7. Demand pump at water heater with dedicated return line. From Kruger/Seville. Green Building, 1E. © 2013 Delmar Learning, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions

Figure 8. One water heater with two circulation pumps. Illustration by Terrel Broiles.

Figure 9. Two heaters with no demand loops. Illustration by Terrel Broiles.

Multifamily Midrise Options

  • Central hot water line with one demand pump. Install a central hot water trunk line with a demand pump near the heater and controllers at each use point to operate the pump when hot water is needed (Figure 10). Locate all fixtures within the pipe length requirements of Table 1, Column B.
  • Figure 10. Central water line with one demand pump. Illustration by Terrel Broiles.

  • Central hot water line with multiple demand pumps. Install a central hot water trunk line with demand pumps near groups of fixtures and controllers at each use point to operate the local pump when hot water is needed. Locate all fixtures within the pipe length requirements of Table 1, Column B.
  • Multiple hot water lines with demand pumps. Install hot water trunk lines with demand pumps at each group of fixtures and controllers at each use point to operate pumps when hot water is needed. Locate all fixtures within the pipe length requirements of Table 1, Column B.
  • Central hot water line with heat tracing. Install a central hot water trunk line with electric heat tracing to maintain a temperature of 125 degrees (52ºC). Locate all fixtures within the pipe length requirements of Table 1, Column B. In multifamily buildings where a demand pump will operate more than six hours per day, heat traced piping can be an energy-efficient alternative, especially if insulated.

Volume Performance Test

For projects using Option 2, the Green Rater must perform a test according to the following procedure (adapted from WaterSense for Homes criteria):

  • Before testing, check faucets, showerheads, and all other hot water fixtures to make sure there is no hot water in the pipes. If there is hot water in the pipes, wait until all water has cooled to room temperature before performing the test.
  • Determine whether the hot water system is a compact traditional system, a circulation loop system, or a heat traced pipe. Verify that the water heater is on.
  • Select the fixture that is located farthest from the hot water source (water heater, circulation loop, or heat traced pipe).
  • If a circulation loop is installed, confirm that it operates on demand and is not a timer-, temperature-, or convection-based circulating system; turn on the switch (or operate the motion sensor or other controller for the hot water pump) and wait about 40 seconds, or until the pump turns off.
  • Place a bucket or a flow-measuring bag marked for 24 ounces (0.71 liter) underneath the selected hot water fixture.
  • Turn the hot water completely on and place a digital thermometer in the stream of water; record the starting temperature.
  • Once the water meets the marked line, turn off the water and record the ending temperature.
  • The temperature must increase by a minimum of 10ºF (5ºC).

Example Calculation for Determining Pipe Lengths

A project home has 14 feet of ¾-inch type L copper pipe in the trunk line and 8 feet of ½-inch type L copper pipe in the branch line to the farthest lavatory (Figure 4). Since the largest size pipe is used to calculate the distance, this layout does not meet the requirements of a maximum of 21 feet of pipe (Table 1). The volume of the 14 feet of type L ¾-inch copper pipe, at 3.22 ounces per linear foot, is 45.08 ounces, and that of the 8 feet of ½-inch type L copper pipe, at 1.55 ounces per linear foot, is 12.4 ounces. Thus the total volume of water in the lines from the water heater is 57.48 ounces, meeting the requirements for Path 2, maximum pipe volume (Table 2).

Example Calculation for Determining Volume in Pipes

A project home has 8 feet of 1-inch PEX CTS pipe between the water heater and the manifold, 1 foot of 1-inch pipe in the manifold between the hot water supply and the tap for the branch line to the farthest fixture, and 30 feet of 3/8-inch PEX CTS pipe to the fixture (Figure 5). There are 31.28 ounces of water in the 1-inch PEX, 3.91 ounces in the manifold, and 19.2 ounces in the 3/8-inch PEX. Thus the total volume of water between the water heater and the farthest fixture is 54.39, meeting the requirements of Path 2, maximum pipe volume (Table 2).

Changes from LEED for Homes 2008

An option has been added for performance testing using EPA WaterSense testing procedures.

Contract Language Recommendations

Plumbing contractor:

For a compact system design, locate the water heater or heaters close to all hot water fixtures so that the hot water pipe from the heater to the farthest fixture is no longer than 21 linear feet (6.4 meters).

For a demand circulation loop design, install the hot water circulation loop such that the branch line between the circulation loop and the farthest hot water fixture is no longer than 16 linear feet (4.9 meters). The pump must be operated by a controller that draws water into the circulation loop only when required and turns off as soon as water temperature at the pump or remote thermostatic sensor is increased by 10ºF (- 12ºC). Provide remote pump controls at each hot water fixture.

Install continuous insulation on all hot water pipes from the water heater to the fixture or finished wall. Where insulated pipes penetrate structural members and walls, insulation must be continuous unless otherwise required by code or the local building official. The insulation thickness must at least equal the pipe diameter, have a maximum thickness of 2 inches (50 mm), and have a minimum value of R-4. Seal all seams and joints in the insulation with tape or solvent according to the manufacturer’s instructions.

Technical Resources

Alliance for Water Efficiency: Residential Hot Water Distribution System Introduction
allianceforwaterefficiency.org/Residential_Hot_Water_Distribution_System_Introduction.aspx

Exemplary performance

Not available.

Verification and Submittals

Verification team:

Efficient Hot Water Distribution

  • Conduct on-site verification that installed hot water distribution system meets requirements for plumbing run lengths and pipe diameter.
  • Conduct on-site verification that installed recirculating system includes push-button controls and automatic pump shut-off controls.

Performance Test

  • Conduct test to determine volume of water in hot water plumbing runs.

Pipe Insulation

  • Conduct on-site verification that installed hot water distribution system meets requirements for pipe insulation.

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