Hot Water Recirculation Pumps

How a recirculation pump works

Without recirculation, the water in your hot line cools off between uses. Open the tap and that cold water has to come out before the hot arrives. Rheem describes exactly this: the cold water sitting in the pipes runs down the drain while you wait.

A recirculation pump closes the loop. It moves hot water from the heater out through the pipes and back again, so hot water is already at the fixture when someone opens it. Rheem claims a household can save up to 12,000 gallons of water a year this way. That's the manufacturer's figure, and your number depends on your pipe runs and habits.

Picture the diagram as a circle. Hot water leaves the top of the heater, runs to the farthest fixture, and comes back to the heater's cold inlet or drain connection. The pump sits somewhere on that circle, and a check valve keeps water from flowing backward. Grundfos's install guide calls for a non-return (check) valve and a shutoff valve with the pump.

The two types

Dedicated return line

This is the classic system. A separate pipe runs from the end of the hot line back to the heater. It's common in newer custom homes and houses where the plumber planned for it. The pump mounts on that return pipe. It works well and doesn't touch your cold line, but retrofitting a return pipe means opening walls.

No return line (crossover or "comfort" systems)

Most existing homes don't have a return pipe, so these systems use the cold line as the return. A pump goes at the water heater, and a valve goes under the farthest sink, connecting hot to cold. When the water in the hot line cools, the valve lets it flow back to the heater through the cold pipe. Navien sells a valve for this called NaviCirc, built for recirculating hot water where there's no dedicated return line. Grundfos's Comfort System uses the same idea.

The trade-off: the first few seconds from the cold tap at that sink can come out warm. Most people don't mind. Some do, especially for drinking water.

Pump control: always on, timer or on demand

How the pump decides when to run matters more than which brand you buy.

We'd skip the always-on setting. A pump running around the clock keeps the whole hot line warm, and that heat leaks out of the pipes the entire time. A schedule built around mornings and evenings, or a push button by the sink, gets most of the comfort for a fraction of the energy.

Many pumps also have a temperature sensor, sometimes called an aquastat, that shuts the pump off once the return water is hot. Grundfos's version attaches to the supply pipe, and for that version the company recommends setting the water heater above 120°F.

Tankless water heaters and recirculation

Tankless units can recirculate, but not all of them handle it well. A tankless heater only fires when it senses enough flow, and short bursts can cause the "cold water sandwich," a slug of cold water between two hot ones. A.O. Smith suggests a model with a built-in buffer tank as one fix.

Some tankless models build the pump in. Navien's NPE-A2 series pairs a buffer tank, a recirculation pump and controls inside the unit. Its pump can run through an external return line or through the existing supply lines using NaviCirc. Rheem's IKONIC SR-Series tankless heaters also have a built-in recirculation pump.

If you already have a tankless unit, check the manual before adding an external pump. Some brands require their own kit or settings, and a mismatched setup can trip error codes. Our guide to tankless water heater installation covers what a retrofit involves.

What it costs

HomeGuide's 2026 cost guide puts replacing a recirculating pump at $150 to $680. Adding a timer to an existing pump runs $100 to $350 installed, or $40 to $140 for the part alone. A crossover kit under a sink is often a one-afternoon job for a plumber. A new dedicated return line costs much more because of the wall work.

Running cost depends on the control mode. A pump on a tight schedule or a push button costs little. A pump left running around the clock costs more in electricity and, more importantly, in heat lost from the pipes.

What to skip

• Skip the always-on mode unless the pump also has a temperature shutoff.
• Skip a pump with no check valve in the system. Without one, water can flow backward through the heater.
• Skip a recirculation pump if your real problem is a heater that runs out of hot water. A pump moves heat around. It doesn't add capacity. See water heater runs out of hot water.
• Skip one for a single far-off sink if a point-of-use water heater would do the job with no plumbing changes.

Installation notes

Grundfos's installation rules are a good checklist for any brand:

• Follow the arrow on the pump housing for flow direction.
• Put the shutoff valve upstream of the pump and the check valve downstream.
• Mount the pump vertically, horizontally or head-down, never head-up, with the cable facing down.
• Bleed air out after install. Grundfos suggests opening and closing the farthest hot tap 5 to 6 times until the pump runs quietly.
• Insulate the pipes. Grundfos supplies insulation shells for the pump body to cut heat loss, and pipe insulation on the hot line helps every system.

A sediment-heavy tank can shorten pump life, so keep up with water heater maintenance.