Is a hot water recirculation pump worth it?

A recirculation pump keeps hot water circulating through your home's supply loop so it arrives fast at the fixture. Without one, the hot water sitting in your pipes cools off between uses. Open the tap and that cooled water has to clear out before fresh hot water travels from the heater. You wait, and the cold water goes down the drain unused.

The pump closes that gap. It pushes hot water in a continuous or triggered loop from the water heater toward the far fixtures and back. When you open the tap, hot water is already close, so the delay drops from many seconds to almost none. That cuts two things at once: the time you stand waiting, and the clean water you waste while waiting.

The waste is not small. The Department of Energy's Building Science Education Solution Center reports that US households waste 400 billion to 1.3 trillion gallons of water per year waiting for hot water to reach the tap. Treating and pumping all that wasted water takes energy too. The same source puts it at 800 to 1,600 kilowatt-hours per year used to treat and pump water to households that will eventually be wasted. A recirculation system attacks that waste directly.

One design rule matters more than any other. DOE advises placing the circulation loop where it can be kept as short as possible and within 10 feet of every fixture. The closer the loop runs to where you actually draw water, the shorter the final run of pipe and the faster hot water arrives. A loop that stops far from the bathroom still leaves a cold stretch to clear, and that leftover stretch is exactly the water you wait on and waste. Plan the loop around your busiest fixtures, usually the kitchen sink and the main shower, and the system pays back the most comfort per dollar.

There are two common ways to plumb a recirculation system, and the right one depends on whether you are building new or retrofitting an existing home.

The first is a dedicated return line. This is a separate pipe that carries water from the end of the hot run back to the water heater, forming a true loop. It is the better-performing design and the easiest to install during new construction or a major remodel, when the walls are open and a plumber can route the extra pipe cleanly. Because the return is its own line, it does not disturb your cold water.

The second is a comfort valve, also called a crossover valve. This is the retrofit answer. Instead of a new return pipe, it uses your existing cold water line as the return path. A valve mounted under the farthest fixture lets cooled water cross from the hot side into the cold side and travel back to the heater. It is far cheaper and less invasive because no new pipe runs through the walls. The trade-off is that the cold line warms up slightly, so the first draw of "cold" water can feel tepid for a moment.

For most existing Phoenix homes, the crossover valve is the practical choice. There is no easy way to fish a brand-new return pipe through finished slab-on-grade walls and ceilings without opening them up, so the valve that borrows the cold line wins on cost and disruption. For a new build or a gut remodel, a dedicated return line is worth the extra pipe, since the framing is already exposed and the loop can be routed once and forgotten. Either way, this is about getting hot water faster, not about heater capacity. The pump does not make your water hotter or your heater bigger. If you are still deciding on the heater itself, see our pages on tank vs tankless water heaters and water heater sizing.

Because a crossover valve uses the cold line as the return, your cold line can run warm while the pump works. We cover that on whether a recirculating pump heats your cold water lines. If hot water only shows up while the pump is running, see why there's no hot water unless the recirc pump is running.

This is where a recirculation pump earns or loses its keep. The control type decides whether the system saves money or quietly adds to your bill. Get this wrong and a pump can use more energy than it saves.

A pump wired to run continuously keeps hot water moving around the clock, even at 3 a.m. when no one is awake. That means the water heater is constantly reheating water that cools in the loop. A timer-based pump is better, since it only runs during set hours, but it still circulates during stretches when no one draws water. Both can spend more on heating losses than they ever return in convenience.

For a documented Rinnai RSC installation, Smart-Circ versus fixed scheduling explains the manufacturer's learned mode and supported scheduling accessories. Those product details do not establish a saving for every home.

The version that actually saves is demand-initiated, also called on-demand. You press a button or trip a sensor, the pump runs just long enough to bring hot water to the fixture, then it shuts off. DOE says the best way to operate the pump is with demand-initiated controls, and the pump only works when you need it.

ENERGY STAR backs this up. It says demand hot water recirculating systems can save water and energy in some situations, while systems that operate continuously have the potential to use more energy than they save. If you install a recirculation pump, pair it with a demand control. That single choice is the difference between a smart upgrade and a meter that spins faster.

Recirculation tends to pay off more in Phoenix than in many other markets, and the reason is how local homes are built. A large single-story home on a slab foundation spreads its plumbing across a wide footprint. The water heater often sits in the garage at one end, and the master bath can be 50 or 60 feet of pipe away at the other.

Long pipe runs mean a long wait. The farther the water has to travel, the more cooled water sits in the line, and the longer you stand at the tap. In a compact two-story home the runs are short and the wait is minor. In a sprawling ranch-style slab house, the wait can stretch past a minute, and the wasted gallons add up fast on a water bill in a region where supply is tight.

Water heating is also a large slice of the household budget. DOE's Building America Strategy Guideline cites water heating at about 13.1 percent of the energy delivered to residential buildings (2010 Building Energy Data Book). Anything that trims wasted hot water has a direct effect on the bill. In Phoenix, the combination of long runs, expensive water, and high energy use makes the hot water delay more than a comfort gripe. It is a measurable cost.

There is one local note. Phoenix groundwater inlet is warm, so your heater works less hard to reach setpoint than it would in a cold climate. That does not change the recirculation math much, but it does mean the energy lost to a continuously running pump is reheating losses you can avoid by choosing a demand control.

If your main goal is fast hot water at every fixture, our page on how to get instant hot water at every faucet compares return lines, crossover valves and controls.

If you already own a Grundfos Comfort System, our pages on how to install a Grundfos Comfort System pump, how to set its timer and how long its warranty lasts cover the details. The pumps that use a dedicated return line are covered in Grundfos COMFORT pump control modes.

A hot water recirculation pump is worth it if you have a real wait at the tap, you want to stop wasting water and the energy behind it, and you install a demand-initiated control. That combination delivers fast hot water with very little added cost.

It is worth it if you live in a large single-story slab home with long pipe runs, the exact layout common across metro Phoenix, where the delay is longest and the wasted gallons pile up. It is worth it during new construction or a remodel, when a dedicated return line is cheap to add and gives the best result. And it is worth it as a retrofit through a comfort valve, as long as you accept a brief warm spell on the cold side.

It is not worth it if you wire a pump to run continuously or on a wide timer, because the heating losses can outweigh the savings. It is also a weaker case in a small or two-story home where the runs are short and the wait is already brief.

The decision comes down to two questions. Is your wait long enough to bother you and your water bill? And will you control the pump on demand rather than around the clock? If both answers point the right way, a recirculation pump is one of the better comfort upgrades a Phoenix home can make. If you want help matching a system to your home's layout, HQ Plumbing & Air can size and route it so you get fast hot water without a surprise on the next utility statement.

A recirculation pump won't cool a warm cold line. If that's your problem, read why cold water isn't cold after an Arizona repipe.

In Maricopa County food businesses a loop can be required; see the 45 second hot water rule and 60 foot pipe limit.

If your Rinnai tankless heater is part of a recirculation loop and shows a flow code, our page on Rinnai error code 63 covers the checks. In apartment buildings, a weak recirculation loop is a common reason the upper floors go without; see why upper floors lose hot water.

It helps to first understand why the wait for hot water happens.