Gradually over the years a lot of things have changed, and a lot have not. For instance, gone are the days when opening your faucet wide open produced flows of 10 gallons per minute. Over time water has become much more valuable, and measures have been put in place to conserve water. These days all fixtures have flow restrictors and you just can’t get a 10 gallon per minute flow rate. The shower has pretty much been reduced to 2 gallons per minute and the bathroom sink to about ¾ gallon per minute.
Years ago it was HVAC Contractor & Technician common in expensive homes to find hot water circulating systems that provided the home owner with instant hot water at any fixture in the house. The plumber would run the hot water piping in a loop from the water heater outlet to a fixture and from that fixture to the next and so on until he reached the last fixture. From the last fixture he would run a pipe back to the inlet of the water heater where a pump and check valve were located.
The pipe from the last fixture back to the water heater is known as a dedicated return line. A check valve located between the return line and the water heater inlet kept water from being drawn backwards through the return line when a fixture was in use. There would be a pump located either at the water heater outlet or at the return line at the water heater inlet, that would circulate the hot water through the hot piping, keeping hot water in the piping all of the time. That way when ever a hot water tap was turned on there would be instant hot water.
Instant water is wonderful, but it is expensive. By keeping the hot water piping full of hot water all the time a great deal of heat energy is being lost from the piping, even when fully insulated since there is so much darned surface area on a piping system. With the full time circulating system you not only pay for the heat energy being lost from the plumbing, but also you pay for the energy to run the pump all the time, and your water heater doesn’t last as long. You can put the pump on a clock timer and shut the system off during times of little use, but that can be quite an inconvenience and the system will still waste huge amounts of energy.
A nice side benefit of instant hot water is the conservation of water. You don’t run thousands of gallons per year of water down the drain waiting for hot water to arrive.
One of the problems with hot water circulating systems is that they do not work with tankless water heaters which are becoming very popular. The problem is that tankless water heaters are turned on when water flows through them. Since the circulating system continuously circulates the hot water, the water heater would be on all of the time. That just wouldn’t work out very well. It’s unfortunate since tankless water heaters take a little longer than storage heaters to deliver your hot water.
However, considering the cost of both energy and water these days there should be a way of saving both. The good news is that there are systems that can do both. These systems are known as “demand” hot water systems since the user must demand hot water to get it. The way the user typically demands hot water is by pressing a button near the fixture.
Most demand systems are marketed toward existing homes that do not have a dedicated return line. A return line can be very expensive to install, but there are some systems now that do not require a return line. These systems use the cold water piping as the return line.
The pump is located at the fixture furthest from the water heater and is connected to the hot and cold water lines. When the pump is activated it pumps water from the water heater through the piping and then into the cold water line and on back to the water heater. When the pump detects a rapid increase in temperature it shuts off, and hot water is now just a couple of seconds away once the tap is turned on.
Since the pump only runs for a few seconds, and only when hot water is needed, it uses very little energy. Typically a demand system uses about $1. 00 or $2. 00 per year in electricity. The water heater does not use any more energy than a normal system uses, and a typical family of four can save up to about 15, 000 gallons of water per year. Typically these pumps can pump the water to the fixture about twice as fast as by running the tap at full blast.
Another nice feature of demand hot water systems is that they will work fine with tankless water heaters since they don’t circulate the water, just deliver it. Some demand systems models manufactured by Metlund and Taco do not have enough power to turn on the tankless heaters, so check before you purchase if you have a tankless heater. The Chilipepper appliance, a demand system manufactured by Chilipepper Sales is powerful enough to run any tankless water heater, and is less expensive than the Metlund D’Mand Systems and the Taco systems.