Have you ever experienced the problem of turning on a faucet for hot water and getting only cold water for quite a long while until, finally, hot water arrives? In many homes, this is a substantial problem…especially in houses with two or more floor levels. This can result in delays lasting for several minutes. Usually, the water heater is not to blame. The cause of this annoying delay is the simple fact that there is a long “pipe run” from the hot water system in the basement to the faucet upstairs.
If nobody has drawn hot water from that faucet for a while, then all the hot water in the piping has cooled-down to room temperature. That means you have to run that faucet long enough to exhaust all the cold water until hot water finally arrives. This not only wastes your time and inconveniences you but it also loses all that water down the drain. In some towns the cost of supplying potable water is considerable and, over a year, this can add up.
So, what is the solution? Hot water recirculation. It’s straightforward and works like this: The plumber installs a “T” fitting into the hot water pipe in the wall behind (or below the floor under) the faucet using hot water that is the farthest away from the water heater. The branch of this “T” is connected to a water pipe (half-inch size is good), and this pipe is extended down through the building and over to the water heater. Finally, this pipe is connected to the cold water inlet of the water heater with a “swing check valve.” This valve is installed so that it will allow the water to flow only into the ever in the opposite direction.
The net result of all this is that a CONVECTION CURRENT will begin moving the hot water from the water heater in the basement through the traditional hot water piping to the faucet upstairs and will return to the heater by way of the recirculation piping. The water will move (slowly but continuously) in a circle from the heater to the faucet to the heater to the faucet, etc., and will be delivering hot water to the faucet “24/7”. Moreover, the benefits of this recirculation piping are not limited to just that faucet. Any plumbing fixtures or faucets using hot water between the water heater and the faucet upstairs will also experience a faster response.
What makes the water move? Simple…CONVECTION CURRENT. This is a simple principle of physics. When there is a temperature difference of as little as seven (7) degrees Fahrenheit in the entire system (water heater, water piping, recirculation piping), then the water will move. Water that is hotter is also lighter and wants to rise the pipe.
Conversely, water that is cooler is also denser and wants to sink the pipe. This is what causes the water movement. Since there is a one-way flow device (the “swing check valve”) installed in the piping, the water has to flow in the right direction which is most beneficial to delivering hot water to the farthest fixture or faucet. Many people falsely believe that a pump must be installed to move the water mechanically. This is not only untrue but will naturally increase the cost to fix the recirculation piping.
In some more substantial houses, it is advantageous to install more than one recirculation pipe. When joining two such tubes in the basement (to a “common pipe”) that continues back to the water heater, the standard pipe should be one pipe size larger. As an example, two half-inch recirculation pipes should be connected to a 3/4 inch size standard pipe. Three half-inch recirculation pipes joined together in the basement should be connected to a one-inch size standard pipe. The swing check valve should be the same size as the standard pipe. In some houses that have cold, drafty basements (typical of many old houses), the hot water and recirculation piping should be insulated throughout the, or the convection current may not work during the cold months.