Hot Water Recirculation Pumps: Instant Hot Water Options Compared

The short answer

A recirculation pump keeps hot water moving so it reaches the tap in seconds instead of running cold water down the drain. Homes with a dedicated return line mount the pump at the water heater. Homes without one use an under-sink crossover kit that sends cooled water back through the cold line from the farthest fixture. Run it on a timer or on demand rather than continuously: continuous recirculation can waste more energy in heat loss from the pipes than it saves in water.

The two system types

Return line vs crossover systems
	Dedicated return line	Under-sink crossover
Plumbing needed	A separate hot-water return pipe to the heater	None; uses the existing cold line
Pump location	At the water heater	At the heater, with a crossover valve under the farthest sink
Side effect	None	The cold tap at that sink runs lukewarm briefly
Best for	New builds, homes already plumbed with a return	Retrofits in existing homes

Timer, thermostat or on demand

Continuous: instant hot water always, but pipes lose heat all day; the least efficient option.
Timer: runs during morning and evening peaks only; a good balance.
Thermostatic (aquastat): runs until the return water reaches a set temperature, then stops; saves energy versus continuous.
On demand: a button, motion sensor or app starts the pump for a minute before you use the tap; the most efficient.

Pumpendium mathWater saved: if a bathroom takes 45 seconds to run hot at 2 gpm, each use wastes 1.5 gallons. Four people, three uses a day each, is about 18 gallons a day, roughly 6,500 gallons a year that recirculation can save.

Running costs

Most residential recirculation pumps draw roughly 10 to 50 W, so the pump's own electricity is small. The bigger cost is heat lost through pipe walls while the loop stays hot. Insulating the hot and return lines reduces that loss substantially and is worth doing alongside any recirculation install.

Tankless heatersTankless water heaters: many require a minimum flow to fire and some limit recirculation. Use a pump the heater maker approves, or a tankless model with a built-in recirculation pump.

Installation notes

Use a pump rated for potable water: bronze or stainless, not cast iron.
Put the crossover valve under the sink farthest from the heater.
Fit check valves as the instructions specify so water does not flow backwards when the pump is off.
Insulate exposed hot and return lines.

Products mentioned

Hot water recirculation · Grundfos

Grundfos Comfort System 595916 Recirculation Pump

Timer, 0-9 GPM.

Grundfos

Hot water recirculation · Laing

Laing AutoCirc LHB08100092 Recirculation Pump

14 W, 24-hour timer.

Laing

Hot water recirculation · A. O. Smith

A. O. Smith APCOM UT1 Recirculation Pump

Thermostat plus timer.

A. O. Smith

Questions readers ask

Are hot water recirculation pumps worth it?

They save water and waiting time, especially in long or spread-out homes. Run them on a timer or on demand, and insulate the pipes, so energy losses do not cancel out the savings.

Do I need a return line for a recirculation pump?

No. Under-sink crossover kits use the existing cold line as the return, at the cost of briefly lukewarm cold water at that sink.

How much electricity does a recirculation pump use?

Typically 10 to 50 W while running. Heat lost from the hot pipes is the larger cost of continuous operation.

Can I use a recirculation pump with a tankless water heater?

Often, but check the heater maker's requirements; some tankless units need approved pumps or have recirculation built in.