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Hot Water EfficiencyWater

How do on-demand re-circulating hot water pumps work?

These systems are designed to move hot water from your water heater to your most remote fixture within seconds. At the push of a button the cool water you normally let run down the drain is circulated back to the water heater through the cold water line so it isn’t wasted. Systems can easily be installed under the sink farthest from your water heater.

Learn more about these systems here.

What are the two types of systems that work with existing hot water storage tanks?

  1. Hot Water Demand System (electrical pump system)
    The Hot Water Demand system (HWDS) is an electric water pumping system that quickly (typically within 30 seconds) brings hot water to the fixture by drawing water from the hot water tank and returning cooler water to the hot water tank where it is reheated. The HWDS is usually installed under the sink farthest from the water heater. At the push of a button, it circulates the water normally discarded down the drain back to the water heater through the cold water line. Simultaneously, the HWDS pumps hot water from the hot water heater to the fixture. When a predetermined temperature (usually 5°F above room temperature) at the fixture is reached, the pump stops automatically and hot water is available at the faucet. The pump may be operated by a switch placed next to the fixture or by a remote control.
  2. Hot Water Valve (non-electrical)
    This is a mechanical control valve installed at the point of use. When the water in your hot water pipe and the control valve cools below about 85 degrees F (user adjustable), the thermal materials within the control valve contract, and silently open the valve. Thermal convection naturally circulates the cooled water through your existing cold water pipes and back to the hot water tank for reheating. Your existing hot water tank now uses less energy reheating 85 degree F water instead of cold ground temperature water. When hot water reaches the control valve, the valve automatically closes. This maintains hot water at the control valve without wasting water or energy. When you mount the hot water control valve in the fixture furthest from your hot water tank all other fixtures in your house also benefit. No electricity is necessary. Note: Circulation of water by thermal convection must not be restricted (no check-valves) between the hot water tank and the control valve.

How do you activate hot water systems?

Systems can be activated by an on/off button, motion sensor, thermostat or timer. Thermostats or timers automatically turn on the pump whenever water temperature drops below a set-point, or when the timer reaches a setting. Although these systems ensure that hot water is always available at the faucet without any waiting, they may use more energy than an on/off button due to more frequent recirculation cycles.

For more information, see H2OUSE.org and CUWCC Hot Water Articles

How do instant “tankless” hot water systems work, and are they helpful in conserving water?

While limiting wait time these may or may not help with water conservation. These can be installed with gas/propane or electrical connections. They do not require a tank for storing and maintaining hot water. Water is heated instantly and on demand only, eliminating the need to store and constantly heat water. Tankless water heaters can provide an endless supply of hot water which means the capacity of your water tank does not limit the use of hot water.

What factors should I consider when purchasing a tankless water heater?

  1. Simultaneous Water Usage Needs
    Do you need to run 2 showers at the same time or maybe a shower and a couple sinks? Use a 2.5 gpm flow rate for a shower and 1.0 gpm for a lavatory sink as a reference point to determine your total simultaneous water needs. For example, if you are running 2 showers at the same time, you will be requesting 5 gallons per minute from the tankless water heater.  If you were running a shower and the washing machine at the same time, you would be requesting 5 ½ gallons per minute from the water heater.  In either of these situations, you would need something that produces at least 5-5 ½ gallons per minute.
  2. Gas vs. Electric
    Sometimes you have a choice between gas and electric. The gas units are typically more powerful than the electric units and are more energy efficient.  The most important considerations for a gas installation are the venting, proper gas line sizing, combustion air requirements and venting of combustion gases.  The electric tankless water heaters are hard wired and typically have high amperage requirements; however, there is no combustion air or venting requirement with an electric unit. This means an electric unit can be cheaper to install, but remember that electricity is a more expensive form of energy than gas.

For more information, see Energy Star Tankless Water Heaters.

Last Updated: May 20, 2013