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Domestic Hot Water Return Piping

Domestic Hot Water Return Piping

Domestic hot water return piping is used in applications where the occupants need or desire to have hot water available right at the tap all the time at a moment's notice. Hot water return piping is closely regulated and strict adherence to the current building code is an absolute must when designing and ultimately building your project.

Not adhering to the current governing code could result in permit rejections, your building project being shut down, delays, and loss of your investment. It is especially important for hot water Return Piping applications to be code compliant due to the potential for injury if the installation or design of the system is flawed.

Historically, there have been instances where sub-par materials were utilized and that ultimately caused problems. In general, the piping system will need to be made of non-ferrous bronze or stainless steel plumbing parts with ideally copper piping. Be sure to check with your local governing body to ensure you are referencing the correct codes.

Building Code

The 2015 International Plumbing Code section 607.2 has the following language:

"607.2 Hot or tempered water supply to fixtures. The developed length of hot or tempered water piping, from the source of hot water to the fixtures that require hot or tempered water, shall not exceed 50 feet (15 240 mm). Recirculating system piping and heat-traced piping shall be considered to be sources of hot or tempered water.

607.2.1 Circulation systems and heat trace systems for maintaining heated water temperature in distribution systems. For Group R2, R3 and R4 occupancies that are three stories or less in height above grade plane, the installation of heated water circulation and temperature maintenance systems shall be in accordance with Section R403.5.1 of the International Energy Conservation Code.

For other than Group R2, R3 and R4 occupancies that are three stories or less in height above grade plane, the installation of heated water circulation and heat trace systems shall be in accordance with Section C404.6 of the International Energy Conservation Code.


607.2.1.1 Pump controls for hot water storage systems.
The controls on pumps that circulate water between a water heater and a storage tank for heated water shall limit operation of the pump from heating cycle start-up to no greater than five minutes after the end of the cycle.

607.2.1.2 Demand recirculation controls for distribution systems. A water distribution system having one or more recirculation pumps that pump water from a heated water supply pipe back to the heated water source through a cold water supply pipe shall be a demand recirculation water system. Pumps shall have controls that comply with both of the following:

The control shall start the pump upon receiving a signal from the action of a user of a fixture or appliance, sensing the presence of a user of a fixture, or sensing the flow of hot or tempered water to a fixture fitting or appliance.

The control shall limit the temperature of the water entering the cold water piping to 104 F (40C).
607.2.2 Piping for recirculation systems having master thermostatic valves. Where a thermostatic mixing valve is used in a system with a hot water recirculating pump, the hot water or tempered water return line shall be routed to the cold water inlet pipe of the water heater and the cold water inlet pipe or the hot water return connection of the thermostatic mixing valve.”

This is included as an example to show how complicated the codes are and can be in regards to construction. The codes themselves are such to prevent people from being harmed and to ensure the buildings that are built are safe and habitable for years to come. Consult with your MEP engineer to ensure your design or existing structure is up to code.

Project Planning

Designing and planning a domestic hot water return piping system is not an easy task. You will want to find and engage the services of a qualified MEP engineer to aid you in completing a functioning design. There are a few factors that will need to be taken into consideration before you even make the decision that your project will need a domestic hot water return piping system. You will need to ascertain & consider

  • The immediate volume demand for hot water
  • The need for the hot water to be hot right at the point of extraction
  • The ultimate building use
  • Future occupancy possibilities
  • Future volume demand for hot water
  • Building code regulations and restrictions

Other considerations when designing a domestic hot water return piping system are

  • Where the water will be routed prior to the extraction point - this impacts the length of time it takes for the water to reach the extraction point
  • Creating a balanced system that will result in equal flow in all branches
  • Mitigating and minimizing the potential flow velocity - this will prevent erosion in the copper piping of the system

Addressing these points and facets will help you design a well thought out and effective domestic hot water return piping system. Designing it well from the start will alleviate the need for retrofitting or major changes later in the lifetime of the system.

Choosing the engineer early process means you have an expert on your side who will help you navigate the building codes, governing bodies, and design process for your project. They will be your best advocate and a way to ensure your project has the best chance of success.

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