Hot Water Delivery System

As is well known, a fair amount of water is usually wasted while waiting for hot water to come through the tap. Hot water delivery systems (also known as a hot water re-circulation systems) are designed to re-circulate the cold water in the pipes back to the hot water heater until hot water is available rather than letting it just flow out of the tap. While it is much easier to include this type of system when a home is first built, some systems make water and money savings available to existing homes by retrofitting them with re-circulation technology.

There are three basic approaches to re-circulation systems:

1. On Demand/Self-Activated (a button is pushed to start the system)
2. Timer-controlled
3. Thermostat-controlled

Because Timer-based systems will begin circulating and reheating the water for the set period whether or not the hot water is being used, these systems are usually not recommended for energy conservation reasons. Thermostat-controlled re-circulation systems are also, in general, not recommended for the same reasons. On Demand/Self-Activated systems include a measure of delay with use, but conserve energy as well as save water.A variety of research reports have been published analyzing the water and energy wasted or saved when considering a hot water delivery system. One report estimated that 20% of hot water usage is wasted while waiting for the hot water to actually come out of the tap. For one newly constructed home, water wasted while waiting for the hot water equaled over 7 gallons in the nearer part of the house to over 10 gallons at the farther side of the house. For another property, water wasted equaled 2.3 to over 4 gallons wasted for each “cold start”. Because the current plumbing design has such an impact, a custom analysis of your current hot water use when compared to the estimated efficiency and cost of the proposed system will help you to determine what makes sense for your family.

Minimum Requirements

Hot water delivery options as defined by the Energy Star “Volumetric Hot Water Savings Guidelines:”

(a) Dedicated re-circulating Line – This method of re-circulating hot water requires specially designed plumbing where the hot water pipe from your water heater is plumbed to each fixture in a loop fashion, and then continues back to the water heater through a third line (return line). A small pump re-circulates the hot water in a continuing loop, only shutting off with a timer or thermostat.
(b) Whole house manifold systems – Whole house manifold systems, also called parallel pipe or home run systems, use small diameter, flexible pipes that run directly to each individual fixture from a central manifold located near the water heater. The manifold may be either plastic or metal, and the piping consists of flexible plastic piping such as PEX, which is a high- temperature, flexible polymer pipe. For example, bathroom sinks and showers would be on their own hot water line from the water heater.
(c) Demand initiated re-circulating systems – The user initiates demand-initiated re-circulating systems by pushing a button or via a motion sensor located near the hot-water fixture. Pumps are used to send cold water in the pipes back to the water heater through a dedicated return line or the cold water line and pull hot water from the water heater to where it is needed. When the pump is operating, a sensor measures a change of temperature and turns the pump off when the desired temperature change is met.
(d) Core plumbing systems – A core plumbing system is a system that has a central plumbing core, where the kitchen, the bathrooms, and the laundry room are in close proximity and the water heater is centrally located beneath the central plumbing core. The system is designed to minimize the total volume of pipe by limiting run lengths and designing the system in a tree-like structure with trunks, branches, and twigs, where longer pipe lengths have a much smaller pipe diameter.

Please see these EnergyStar Guidelines for more information.