Do Hot Water Recirculating Systems Save Money?

Nope. They might save a bit of water but they use a lot of energy.

There's nothing better than a long hot shower. And it's also nice to get the hot water right away, which is one reason that people like recirculating pumps. Sometimes they are pitched as a way of saving energy and money, so years ago we had our expert look at it in Ask Pablo: Will a "Water-Saving" Hot Water Recirculation Pump Really Save Me Money?

Recirculating pumps were pitched as a great way to save water because people wouldn't then leave the shower or sink running while they waited for the slug of cold water in the pipes to be pushed out by the hot water from the tank. Pablo did the math and determined that a lot of energy was lost as the hot water radiated from the pipes, costing way more than is saved in water costs. He noted also that people weren't really putting these things in to save water, but for the convenience of having it hot instantly.

Pablo wrote that post in 2011 and the comments have been coming in ever since, including gems like "Good god. This Pablo guy is an absolute joke."

Martha's Vineyard Case Study

Fortunately, over at Green Building Advisor, (alas, behind a paywall) Engineer and energy expert Marc Rosenbaum has had a look at the issue. Marc had worked on a big vacation home on Martha's Vineyard where the client wanted a recirculating system.

The first weekend that the owners were there, I got a call: ‘We’re out of hot water.’ I learned that the rich are not like you and me. On Martha’s Vineyard, people like outdoor showers, and sometimes five people take showers one after the other. The owners said, ‘We need more hot water storage, and we don’t want intermittent recirculation. We want continuous recirculation.’”

Marc and his team added more water heaters and storage, and monitored the power consumption when the house was not occupied.

“The total daily kWh usage for hot water was 3.94 kWh without recirculation. With recirculation, the daily usage was 12.30 kWh — three times as much energy as the system used without recirculation. That’s 3,044 kWh per year for recirculation — enough energy to make 100 gallons per day of domestic hot water. So continuous recirculation is a bad idea.”

Recommendations

Seriously, so much energy just so that they can all have instant hot water. They clearly haven't heard about the new standard for luxury. And this Pablo guy knew his stuff with his recommendations, which I have updated a bit:

Insulate your pipes. Whether or not you have a recirculating pump, this will significantly reduce heat loss.
Design the system properly with short straight runs.
Don't waste the water while you wait for it to get hot. Put a bucket under it and use it.
Sing a song or do something to fill those seconds until the hot water flows. Seriously, is it that big a deal?