Hot Water Recirculation – Instant Hot Water Systems Explained

Hot water recirculation systems are often referred to by a variety of names, all meaning pretty much the same thing. Recirc pumps, recirculation pumps, recirculating pumps, and circulation pumps are all the same.

In our context they all refer to the practice of circulating hot water through your plumbing so that you have quick hot water and don waste water running it down the drain while you are waiting. As with most good things there are trade-offs with hot water recirculation systems.

First, let’s examine a basic recirculation system and get familiar with how it works. The system consists of the water heater, a pump, and a loop of pipe coming from the outlet of the water heater, going from sink to sink in a looped fashion, and returning from the last sink back to the pump which has its outlet connected to either the inlet to the water heater or to the drain valve.

Recirc pumps
Often called recirc pumps, as well as recirculation pumps etc. the hot water circulating pumps are designed to slowly circulate the hot water through the piping at a low velocity. There is no need for high flow since a nice low flow still keeps the water piping hot through the entire system. High flow rates run continuously can also lead to pipe erosion and eventually require replacement of the pipes.

Instant Hot Water

As you can see, such a system will provide you with nearly instant hot water. This can save tremendous amounts of water that would have been run down the drain while you waited for the hot water to arrive at the fixture. The penalty you pay is in the cost of the energy consumed keeping your giant radiator system hot.

The water heater has to fire up more often and for longer to keep the temperature from falling as the heat energy is let loose on the environment.

You can minimize your energy costs by putting the pump on a timer so that it only runs when there are people around that may want to use hot water. Leave it off late at night and during the day if no one is home during the day. It still wastes a lot of energy but you can easily cut your losses in half in most cases.

The downside is of course, if you want hot water when the pump is not running you will have a lengthy wait. If you don’t have a length wait you probably didn’t need a hot water recirculation system to begin with.

Another way to control the traditional hot water recirculation systems is with temperature control. Have the pump turn on when the temperature drops to some pre-set value, like 100 degrees, and when the temperature reaches 120 degrees turn the pump off. The temperature sensor is called an aquastat, and usually clamps onto the hot water pipe near the pump.

Since you still have piping full of hot water for long periods of time you are still wasting a lot of energy.

If you do have a hot water recirculation system you should insulate all of the hot water piping to minimize the heat loss.

Tankless Water Heaters

Tankless water heaters generally don’t work with hot water circulating systems since for one thing most hot water pumps don’t produce enough flow to turn on tankless water heaters. They usually require at least ½ gallon per minute to operate.

Hot water recirc systems also cause the water heater to cycle on and off frequently since there is no tank for storage. With many brands of tankless water heaters a hot water circ system will void the warranty.

Tankless water heaters take longer to deliver hot water than tank type water heaters and so it’s too bad hot water recirculation systems don’t work with them.

Well that’s about it for hot water recirculation systems, a water heater, a pump, some hot water piping and a few faucets. Don’t forget the pipe insulation.

Bill the Hot Water Guy