## 5.4 Prescriptive Requirements for Water Heating

### 5.4.1 Single Dwelling Units

§150.1(c)8

There are five options to comply with the prescriptive water heating requirements for newly constructed single dwelling units. For all five options, the water heater must comply with the mandatory requirements for water heaters. (See Section 5.3.) If a recirculation distribution system is installed, only demand recirculation systems with manual control pumps are allowed. The five options are described below.

Option 1: Install one or more natural gas or propane instantaneous water heater with an input rating of 200,000 BTU per hour or less and no storage tank.

Option 2: Install a single natural gas or propane storage water heater with a rated storage volume 55 gallons or less and an input rating of 75,000 BTU per hour or less. In addition, the dwelling unit shall have installed fenestration products with a weighted average U- factor no greater than 0.24, as well as one of the following requirements

1. Use a compact hot water distribution design, which requires a HERS Rater to verify that the system has been designed and installed in accordance with the Energy Standards (See Reference Appendix RA4.4.16.)

2. Use a drain water heat recovery system, which requires a HERS Rater to verify that the system has been designed and installed in accordance with the Energy Standards (See Reference Appendix RA4.4.21.)

Option 3: Install a single natural gas or propane storage water heater with a rated storage volume greater than 55 gallons and an input rating of 75,000 BTU per hour or less.

Option 4: Install a single heat pump water heater. The storage tank shall be located in the garage or conditioned space. In addition, the building must comply with one of the following:

1. A compact hot water distribution design earning the Basic Compact Design –credit and a HERS-verified drain water heat recovery system.

2. For Climate Zones 2 through 15, a photovoltaic system capacity of 0.3 kW direct current (dc) larger than the requirement specified in Section150.1(c)14.

3. For Climate Zones 1 and 16, a photovoltaic system capacity of 1.1 kWdc larger than the requirement specified in Section150.1(c)14.

Option 5: Install a single heat pump water heater that meets the requirements of NEEA Advanced Water Heater Specification Tier 3 or higher. The storage tank shall be located in the garage or conditioned space. In addition, for Climate Zones 1 and 16, a photovoltaic system capacity of 0.3 kWdc larger than the requirement specified in §150.1(c)14 or a compact hot water distribution system earning the Basic Compact Design credit.

If Option 2, 4, or 5 is pursued, then one or more additional building features must be installed as shown above. These features require consideration at the start of the design process, and must be coordinated with several players including the designer, general contractor, sub-contractor, and HERS Rater.

The list of qualified product list of NEEA HPWH can be found here:

https://neea.org/img/documents/qualified-products-list.pdf

For more information on HERS-verified compact hot water distribution design, see Section 5.6.2.4. HERS-verified compact hot water distribution designs are included in Options 2 described above.

For more information on HERS-verified drain water heat recovery system requirements, see Example 5-9 below and Section 5.6.2.5 of this chapter. The Reference Appendix contains the requirements for the proper installation of the system (see RA4.4.21). A HERS-verified drain water heat recovery system is included in Options 2 and 4 described above.

Any other water heating system that differs from the five options described in this section does not meet the prescriptive requirements. Other systems can be installed if using the performance approach as described in Section 5.5.

For additions, the prescriptive requirements described above apply only if a water heater is being installed as part of the addition. The prescriptive requirements apply only to the space that is added, not the entire building.

For alterations where an existing water heater is being replaced, the water heater must meet the mandatory equipment efficiency requirements. Pipe insulation requirements do not apply to alteration for the portion of the pipes that are inaccessible. See Chapter 9 for a more detailed explanation for the water heating alteration requirements.

Example 5-4 − Single-Family Home With Multiple Water Heaters

Question:

A newly built 6,000-ft² single-family home has three gas storage water heaters (40-gallon, 30–gallon, and a 100-gallon unit with 80,000 BTU/h input). Does it comply?
Answer:
In most cases, multiple storage water heaters will result in greater energy consumption than the standard design case (one water heater for a new single-family home). As such, a performance calculation is required since the system does not meet the standard requirements and must be shown to meet the water heating energy budget. However, multiple instantaneous gas water heaters are allowed under Option 1 of the prescriptive method and this house can meet compliance by going that route.

Example 5-5 – Alterations

Question:
If my house has an electric-resistance water heater and I plan to upgrade my water heater, do I need to install a gas instantaneous or gas storage water heater?

Answer

No, if natural gas is not already connected to the existing water heater location, then a consumer electric water heater that meets the requirements of California’s Appliance Efficiency Regulations can replace the existing water heater. If installing new piping to the water heater, then you will need to comply with the mandatory pipe insulation requirements. See Section 5.3.5.1 for more information on pipe insulation requirement and Chapter 9 for more information on alterations.

Example 5-6− Additions

Question:

I am building an addition to my home that will be a self-contained apartment. Do I need to comply with the prescriptive requirements?

Answer:

If the addition will include a water heater, or if it will be connected to the existing hot water distribution system to supply hot water to the apartment, then you must comply with the standards either through the prescriptive or performance path. If taking the performance approach, you can install any type of water heater as long as it 1) meets the requirements of California’s Appliance Efficiency Regulations and 2) does not exceed the water heating energy budget for the self-contained building. If you were adding only an additional room with hot water and not a self-contained dwelling, then the water heating budget would be based on the existing building plus addition. (See Section 5.5.)

Example 5-7 – Heat Pump Water Heaters

Question:

For a new home, can I install an electric water heater? Do I have to perform calculations to show compliance?

Answer:

Yes, electric heat pump water heater (HPWH) can be used for both prescriptive and performance compliance. Calculation is not necessary using the prescriptive compliance path. There are 2 prescriptive options (Option 4 and 5 in Section 5.4.1 above) for HPWH. Option 5 is the simplest option, which requires the installation of a NEEA Tier 3 or higher HPWH in the garage or conditioned space. For climate zones 2 through 15, no additional requirement is needed for compliance. For climate zones 1 and 16, an additional 0.3 kWdc is required in addition to the prescriptive photovoltaic requirement. For more details, see Section 5.4.1 above.

For performance compliance, the characteristic of the HPWH must be modeled, such as rated UEF or make and model of the HPWH if it is NEEA rated.

Example 5-8 – Drain Water Heat Recovery

Question:

I’m in the schematic design phase for a single-family home. I intend to include drain water heat recovery in my design and to follow the prescriptive path. What are the primary design issues I should consider?

Answer:

If you follow the prescriptive path, drain water heat recovery aids compliance only if you are specifying a gas or propane storage water heater with a rated storage volume of 55 gallons or less; or a heat pump water heater that does not meet or exceed NEEA Advanced Water Heater Specification Tier 3. For all water heater type, you could follow the performance path and obtain compliance credit within an energy model calculation. In any case, the initial design issues are related to the selection of an appropriate drain water heat recovery model (i.e. horizontal or vertical type, minimum rated effectiveness, and diameter and length), and designing the layout of the system. If your residence is single story, then a horizontally rated unit is required. If your residence has multiple stories, then the unit can be horizontally or vertically rated. In any case, the required minimum rated effectiveness is 42 percent. The diameter of the unit should match the diameter of the drain pipe. Added length improves effectiveness but requires more space. In terms of the system layout, the unit must recover heat from at least the master bathroom shower and must at least transfer that heat either back to all the respective showers or the water heater. If you desire to maximize savings, you should place the unit in a drain line that serves all the showers and you should pipe the preheated water to the cold side of all the shower mixing valves and the make-up water inlet of the water heater. This is known as an equal flow configuration, since the preheated water flow rate will match the drain water flow rate.

### 5.4.2 Multiple Dwelling Units: Multifamily, Motel/Hotels, and High-Rise Residential

§150.1(c)8

There are two options for using the prescriptive approach to compliance for multifamily buildings:

1. A water heater must be installed in each unit that meets the requirements for a single-family building.

2. A central gas or propane-fired water heater or boiler.

The water heater must have an efficiency that meets the requirements in §110.1 and §110.3 (as listed in Table 5-5). In addition, if a central recirculation system is installed, it shall be installed with demand recirculation controls and a distribution layout with at least two recirculation loops. These prescriptive rules were developed based on studies that found that recirculation pipe heat loss is a major component of energy loss within a central hot water system. Pipe heat loss is affected by the pipe surface area, pipe insulation level, and the temperature difference between the hot water and ambient air. The motivation behind having two loops is to reduce recirculation pipe sizes, thus pipe surface area. This measure reduces energy use and piping materials associated with recirculation systems. Central water heating systems with eight or fewer dwelling units are exempted from needing two recirculation loops.

5.4.2.1 Dual-Loop Recirculation System Design

§150.1(c)8Cii

A dual-loop design is illustrated in Figure 5-7. In a dual loop design, each loop serves half of the dwelling units. According to plumbing code requirements, the pipe diameters can be downsized compared to a loop serving all dwelling units. The total pipe surface area is effectively reduced, even though total pipe length is about the same as or somewhat greater than that of a single-loop design. For appropriate pipe sizing guidelines, please refer to the Universal Plumbing Code.

Figure 5-7: Example of a Dual-Loop Recirculation System

Source: 2013 CASE Initiative: Multifamily Central DHW and Solar Water Heating

Figure 5-7 provides an example of how to implement dual loop design in a low-rise multifamily building with a simple layout. In this example, the water heating equipment is in the middle of the top floor with each recirculation loop serving exactly half of the building. The recirculation loops are located in the middle floor to minimize branch pipe length to each dwelling unit. The figure also illustrates how the solar water heating system and demand controls are integrated.

For buildings with complicated layouts, how to create and locate recirculation loops heavily depends on building geometry. In general, the system should be designed to have each loop serve an equal number of dwelling units to minimize pipe sizes. For systems serving buildings with distinct sections, for example, two wings in an L-shaped building, it is better to dedicate a separate recirculation loop to each of the sections. Very large buildings and buildings with more than two sections should consider using separate central water heating systems for each section. In all cases, simple routing of recirculation loops should be used to keep recirculation pipes and runouts as short as possible. Figure 5-8 provides dual-loop recirculation system designs in buildings with complicated shapes.

Figure 5-8: Examples of Dual-Loop Recirculation System Designs in Buildings of Complicated Shapes

Source: 2013 CASE Initiative: Multifamily Central DHW and Solar Water Heating

Location of water heating equipment in the building also needs to be carefully considered to properly implement the dual-loop design. The goal is to keep overall pipe length as short as possible. As an example, for buildings in regular shapes, locating the water heating equipment at the center of the building footprint rather than at one end of the building helps minimize the pipe length needed to connect the water heating equipment to the two loops. If a water heating system serves several building sections, the water heating equipment would preferably nest between these sections.

With the new prescriptive solar water heating requirement this cycle, it is especially important to consider the integration between the hot water recirculation system and the solar water heating system. Based on feedback from industry stakeholders, most solar water heating systems are configured only as a preheater of the primary gas water heating equipment. In other words, recirculation hot water returns are usually plumbed back to the gas water heating storage tanks, not directly into the solar tank. This means recirculation loop designs should be based mostly on the building layout and are relatively independent of the solar water heating system. On the other hand, gas water heating equipment and solar tanks should be located close to each other to avoid heat loss from pipes connecting the two systems. The preferred configuration is to place both the gas water heating equipment and solar tanks on the top floor near the solar collector so that the total system pipe length can be reduced. As noted before, minimizing pipe length helps reduce domestic hot water system energy use as well as system plumbing cost.

5.4.2.2 Demand Recirculation Control

The prescriptive requirement for domestic hot water systems serving multiple dwelling units requires the installation of a demand recirculation control to minimize pump operation and heat loss from pipes. They are different from the demand controls used in single dwelling units. Demand controls for central recirculation systems operate by sensing hot water demand and recirculation return temperatures. The temperature sensor should be installed at the farthest end of the recirculation loop close to the last branch pipe.

Any system not meeting these prescriptive requirements must instead meet the standard design building energy budget that is established by the energy efficiency performance of a gas instantaneous water heater that meets the requirements of California’s Title 20 Appliance Efficiency Regulations or must follow the performance compliance method for the building as a whole.

Example 5-9 - Multifamily With Individual Water Heater

Question:

We are building a 20-unit multifamily building with individual water heater in each dwelling. Can electric water heaters be used?

Answer:

When there is a water heater in each multifamily dwelling, the requirement is the same as a single-family home. In this situation electric heat pump water heaters (HPWH) can be used for both prescriptive and performance compliance. For more details, see Example 5-7 and Section 5.4.1 above.

Example 5-10 − Multifamily Recirculation System

Question:

We are building an eight-unit, 7,800 ft² multifamily building with a 200-gallon storage gas water heater and a time- and temperature-controlled recirculation system that has 1 inch of insulation on all the piping. The system serves all the units. Do I have to perform calculations to show compliance?

Answer:

Water-heating calculations are required since the standard design assumption uses demand recirculation for the control strategy for central recirculation. Furthermore, solar water heating is a prescriptive requirement for all multifamily buildings with central recirculation systems.

Example 5-11 − Multifamily Large Water Heater

Question:

We are building a 10-unit apartment building with a single large water heater. We do not plan to install a recirculation pump and loop. Does this meet the prescriptive requirements?

Answer:

No. Since it is unlikely that a nonrecirculating system will satisfactorily supply hot water to meet the tenants’ needs, either a recirculating system or individual water heaters must be installed to meet the prescriptive requirements. There is an exception for multifamily buildings of 8 units or fewer.