Quick answer
A hot water recirculation pump is a small pump that moves water from the hot water pipes back to the water heater, so hot water is already near the tap when you open it instead of after the cooled water in the pipe has run down the drain.
It returns water through a dedicated return pipe or, in demand systems, through the cold water line. Energy codes now require controls that run it only when hot water is wanted.
Quick facts
The key facts about Hot Water Recirculation Pump, with sources:
- Job
- Keeps hot water close to fixtures so less cold water runs to drain while you wait 3
- Control rule
- Start on a demand for hot water; stop when the loop is hot and nobody is drawing water 12
- Pipe insulation
- R-3 minimum on service hot water pipe (Washington residential energy code) 2
- Measured savings
- 15% less water-heating fuel with demand plus temperature controls vs. nonstop pumping, in a two-building DOE study 4
- Example pump size
- Under 60 W and 1.32 gpm at 15.4 ft of head for one residential model (Navien NAP-10SS) 5
Key takeaways
- A recirculation pump cuts the wait for hot water by moving cooled water out of the hot pipe before you need it.
- Homes use either a dedicated return pipe or a demand system that sends water back through the cold line.
- A pump that runs all day wastes heat; current energy codes require it to run on demand and stop when the loop is hot.
- Controls matter more than the pump: in a DOE-funded study, smarter controls cut water-heating fuel by up to 15%.
- Hot water in every pipe raises scald risk, so a safe heater setting or point-of-use mixing valves still apply.
What a recirculation pump does
When a hot tap sits unused, the water in the hot pipe cools to room temperature. Opening the tap pushes that cool water out first, and it usually goes down the drain.
The Smart Energy Design Assistance Center (SEDAC) at the University of Illinois cites a U.S. Department of Energy estimate that more than 400 billion gallons of water are wasted each year in the U.S. by people waiting for hot water 3.
A recirculation pump fixes the wait by keeping water moving. It pulls the cooled water out of the hot pipe and sends it back to the tank water heater to be reheated, while fresh hot water moves toward the fixtures.
The result is hot water at the far bathroom in seconds rather than after a long run.
The catch is that warm pipes lose heat. SEDAC warns that many systems run all day, every day, wasting both pumping and heating energy 3. That is why the energy code now cares about how the pump is switched on and off, not only whether it exists.
A pump is not the same as a tankless unit
A recirculation pump does not heat water. It moves water that the heater already warmed. A tankless water heater heats on demand but still leaves cool water in the pipe, so the two are often paired rather than swapped.
How a recirculation loop works, step by step
- A signal starts the pump. In a demand system that might be a push button, a motion sensor or a flow sensor; the 2015 IECC lists all three as allowed triggers 1.
- Cool water leaves the hot pipe. The pump pulls the standing water out of the hot line toward the water heater.
- It returns to the heater. It travels back through a dedicated return pipe or, in a demand system, through the cold water line 3.
- A sensor ends the cycle. A temperature sensor near the end of the loop tells the pump the hot line is up to temperature 3.
- The pump stops. The 2015 IECC text says controls must turn the pump off when the loop is at the desired temperature and there is no demand 1.
- TriggerButton, presence sensor or flow sensor
- Pump runsCooled water leaves the hot pipe
- Return pathDedicated return or cold line back to the heater
- Loop warmsSensor at the far end reads the temperature
- Pump stopsLoop is hot and no one is drawing water
- Back to step 1
Codes in the 2015 and 2018 IECC describe this start-on-demand, stop-when-hot logic. Source: [1] [3]
Types of recirculation systems
| System | How water returns | How it is switched | Where it fits |
|---|---|---|---|
| Dedicated-return loop | A separate return pipe from the farthest fixture back to the heater 3 | Flow sensor at the heater inlet and a temperature sensor at the loop end, per SEDAC 3 | New construction and larger homes |
| Demand system (cold line return) | Through the existing cold water pipe 3 | User button, presence sensor or fixture flow; return water capped at 104°F 1 | Retrofits; pump often under the farthest sink 3 |
| Timer-and-thermostat pump | Either path | Runs during set hours and switches on and off by temperature; one maker’s smallest time block is 30 minutes 6 | Homes with steady daily routines |
| Always-on pump | Either path | Runs continuously; offered as a mode on some units 5 | Not allowed as the sole control under current IECC text 1 |
| Heat trace (no pump) | No return; an electric cable keeps the pipe warm | Must meet IEEE 515.1 or UL 515 1 | An alternative where a return pipe is impractical |
Example: what controls did in a real test
This example uses results from a U.S. Department of Energy Building America study by the ARIES team (Dentz et al., 2016).
It tested controls on recirculation loops in two multifamily buildings against a pump that ran nonstop 4.
The chart shows the cut in water-heating fuel; the table shows the cost side and what each control means for a house.
| Control added | Estimated annual cost savings* | What it means for a house |
|---|---|---|
| Demand control only | 8% 4 | The same idea as home demand systems: a button, presence sensor or fixture flow starts the pump 1 |
| Temperature modulation only | 1% 4 | The smallest gain on its own in the test 4 |
| Both combined | 14% 4 | With controls, the pump ran 14 minutes or less a day 4 |
*Cost savings include knock-on effects on space heating and cooling, as the study reported them. These are apartment buildings with central water heaters, not single houses, so treat the size of the savings as a direction rather than a promise for your home.
Where the pump sits in a house
In a dedicated-return system the pump is usually at or near the water heater, on the return line, with a check valve to keep water moving one way. The Navien ComfortCirc, for example, has a built-in check valve, flow sensor and temperature sensor in one housing 5.
In a demand system that uses the cold line, the pump or its valve is commonly under the sink farthest from the water heater, according to SEDAC’s summary of the 2018 IECC 3. Navien’s manual describes the same idea as a crossover valve at the far fixture 5.
If you are planning a new heater, our water heater sizing tool helps match capacity to the house. A loop adds a small, steady heat loss, which is one more load the heater has to cover.
What a recirculation pump does well, and what it costs you
What it does well
- Hot water reaches far fixtures quickly, so less cold water goes down the drain 3.
- Demand controls let the pump run only minutes a day; the DOE study saw 14 minutes or less 4.
- Small pumps draw little power; one residential model lists under 60 W 5.
- Some units add freeze protection by running in very cold conditions, per Navien’s manual 5.
What it costs you
- Every warm pipe loses heat, which the water heater has to replace 3.
- Poor controls erase the savings; SEDAC notes many systems run around the clock 3.
- Hot water sits at every fixture, which raises scald risk at high heater settings 5.
- Demand systems can send warm water into the cold line, which code caps at 104°F 1.
Limitations to know before you buy
- Uninsulated pipe wastes the gain. Washington’s residential energy code requires R-3 insulation on service hot water pipe 2; bare pipe in a cold crawlspace loses heat fast.
- Compatibility is model-specific. Navien says its ComfortCirc works only with certain Navien water heaters and is intended for a dedicated return line 5.
- Lukewarm cold taps. A cold-line return can leave the first draw from the cold tap slightly warm, which is why the code limits that water to 104°F 1.
- Electric dependence. Timer settings can be lost after a long outage; Grundfos notes the clock may need resetting if power is off more than 15 minutes 6.
- It does not fix low flow. A slow tap is a water pressure or pipe-size issue, not a recirculation one.
What drives the cost of adding recirculation
We do not print prices because fair numbers need dated local quotes. What moves a quote is predictable, though.
The biggest driver is whether a return path exists. A house plumbed with a return pipe needs only a pump and controls. A house without one either needs a new return line, which may mean opening walls, or a demand system that uses the cold line.
Other drivers are the controls you choose (timer, thermostat, push buttons, app control), whether an outlet sits near the heater, how much hot pipe needs insulation, and whether your water heater brand requires its own matching pump.
Running cost depends on how many hours the pump moves water and how much heat the loop loses. Controls are the lever there, as the DOE study shows 4. Our plumbing cost guide explains how plumbers build quotes, and the water usage calculator helps estimate how much water your household uses now.
How a plumber installs one
Installation is plumbing and electrical work. Many areas require a permit for new piping, so ask about it up front.
- Check the layout: Find the farthest fixture and whether a return pipe already exists.
- Pick the system: Dedicated return, or a demand system using the cold line with a crossover valve 5.
- Mount the pump: Install it with isolation valves and a check valve so water flows one way 5.
- Wire the controls: Navien calls for a properly grounded, GFCI-protected outlet for its pump 5.
- Set the controls: Configure demand, schedule or temperature mode; avoid always-on as the only setting 51.
- Insulate and test: Insulate hot pipe to the local energy code (R-3 in Washington) and time how long hot water takes to arrive 2.
Scald and shock risks
With a loop, very hot water is waiting at every tap. CPSC says a 120°F heater setting reduces most tap water scald risk, and that water at 150°F can cause a serious burn in two seconds 7.
Navien recommends thermostatic mixing valves at each point of use if the heater runs hot 5. Plug pumps only into a grounded GFCI outlet, and keep water away from the wiring.
How to keep a recirculation loop efficient
- Check the schedule after power cuts; timer-based pumps may lose the clock 6.
- Keep the pump plugged in during winter trips if it has freeze protection, as Navien advises 5.
- Look for leaks at the pump flanges and valves when you check the water heater.
- Repair torn pipe insulation so the loop does not cool faster than it should.
- If hot water is slow again, have the check valve and sensors tested before replacing the pump.
Warning signs and when to call a plumber
- Hot water takes as long as it did before the pump was installed.
- The cold tap runs warm for longer than a moment.
- The pump hums but water at the far fixture stays cool.
- The pump runs all the time even though it is set to demand mode.
- Water drips from the pump body or its unions.
For leaks, close the valves on each side of the pump and see our plumbing emergencies guide. Our water heater repair and replacement service covers pump and control problems at the heater.
Energy code rules for recirculation
2015 IECC / IRC, R403.5.1.1 and N1103.5.1.1 (as reproduced by the DOE Building America Solution Center at PNNL): heated water circulation systems must have a circulation pump.
Gravity and thermosyphon loops are prohibited; the controls must start the pump on a demand for hot water and stop it when the loop is hot and there is no demand.
Controls, sensors and pumps must be accessible 1.
Demand recirculation, R403.5.2 (2015 IECC): a system that returns hot water through a cold water pipe must start the pump on a user action, a presence sensor or fixture flow, and must keep water entering the cold pipe at or below 104°F 1.
SEDAC lists the same rules under the 2018 IECC as adopted in Illinois 3.
Washington State Energy Code, Residential (WAC 51-11R-40340, effective March 15, 2024): the system return pipe must be a dedicated return pipe, gravity and thermosyphon loops are prohibited, and service hot water pipe needs R-3 insulation 2.
The earlier Washington text, in force until that date, also allowed a cold water supply pipe as the return 2.
Product listings: pumps in contact with drinking water are listed for lead content; Navien’s spec sheet lists NSF 372 and UL 778 for its unit 5. Check which energy code edition your state adopted before you plan a system.
Recirculation pump vs other ways to get hot water faster
| Option | How it helps | Main trade-off |
|---|---|---|
| Recirculation pump with demand control | Moves cooled water out before use 3 | Needs a return path and good controls |
| Always-on recirculation | Hot water at every tap all the time 5 | Constant heat loss; not compliant as the only control 1 |
| Heat trace cable | Keeps the hot pipe warm with electricity 1 | Electric use; must meet IEEE 515.1 or UL 515 1 |
| Heat pump water heater moved closer | Shorter pipe to the main fixtures | Major work; does not help far rooms |
| Pipe insulation alone | Slows cooling in the hot pipe | Does not remove water that has already cooled |
Recirculation myths that waste energy
- Myth A recirculation pump always saves energy.
- Reality It saves water, but a pump that runs nonstop wastes pumping and heating energy, as SEDAC notes 3.
- Myth Any recirculation setup meets code.
- Reality Current IECC text bans gravity loops and requires demand-based controls 1.
- Myth Demand systems heat the cold water.
- Reality Some warm water returns through the cold pipe, but code caps it at 104°F 1.
- Myth The pump heats the water.
- Reality It only moves water; the water heater does the heating 5.
- Myth Washington still allows cold-line returns.
- Reality Its 2024 residential energy code requires a dedicated return pipe for circulation systems 2.
How your state’s energy code changes the choice
The rules depend on which energy code your state adopted. Washington’s residential code, effective March 15, 2024, requires a dedicated return pipe for circulation systems, while the version before it allowed a cold water return 2.
Illinois, under the 2018 IECC as SEDAC summarizes it, still describes both dedicated-return and cold-line demand systems 3. In freezing climates, pipe in crawlspaces and garages loses heat fastest, so insulation and freeze protection matter more. Ask your building department which edition applies before you choose.
Is a recirculation pump worth it for you?
It makes most sense when the far bathroom is a long pipe run from the heater and you wait a minute or more for hot water. It makes less sense in a compact house where fixtures sit close to the heater.
The control choice decides whether you save energy or just water, and the guide below matches the common house layouts to the fix that suits each. Ask for demand control, check what return path your house has, and confirm the local code edition. Our fixture installation service can quote the work.
- If Long wait at one far bathroom
- Then A demand system with a button or motion sensor at that fixture
- If A return pipe is already in the walls
- Then A pump with demand and temperature control on the existing loop
- If No return pipe and walls you do not want to open
- Then An under-sink system that sends cooled water back through the cold line, accepting briefly warm cold water
- If Fixtures sit close to the heater
- Then Insulate the hot pipe and skip the pump
- If A pump already runs around the clock
- Then Add demand control: in DOE field tests it cut fuel more than temperature control alone 4
Source: [4]
Questions about Hot Water Recirculation Pump
Can I install a hot water recirculation pump myself?
Some under-sink kits are sold for owner installation, but the job still means cutting into hot and cold supply lines, mounting a pump at the water heater or a sink, and giving it power, and some areas require a plumbing permit for that work.
A dedicated return loop means opening walls and is plumber work. Read the pump maker’s instructions and check with your building department before you start; if your heater is gas, leave its connections alone.
Do recirculation pumps waste energy?
They can if they run all day. Warm pipes lose heat, and the water heater has to replace it. SEDAC notes that many systems run around the clock.
In a DOE-funded test, adding demand and temperature controls cut water-heating fuel by 15% compared with nonstop pumping, and pump run time fell to 14 minutes or less per day.
Can I add a recirculation pump without a return line?
Yes, with a demand system that sends water back through the cold water pipe, usually with a valve or pump under the farthest sink.
The 2015 and 2018 IECC allow this if the pump starts on a user signal and water entering the cold pipe stays at or below 104°F. Some states, such as Washington since 2024, require a dedicated return instead.
Why is my cold water warm with a recirculation pump?
In a demand system, hot water returns to the heater through the cold pipe, so the first draw from a cold tap can be slightly warm.
Energy codes limit that water to 104°F. If the cold tap stays warm for long, the crossover valve or sensor may not be working, and a plumber should check it.
Should a recirculation pump run all the time?
No. Current IECC text says the controls must start the pump on a demand for hot water and stop it when the loop is hot and nobody is using water. Some units offer an always-on mode, but schedules, temperature control and push-button or sensor demand are the efficient choices.
Does a recirculation pump work with a tankless water heater?
Often, yes, but check the maker. Some tankless and heat pump water heaters work only with their own matching pump; Navien says its ComfortCirc is compatible only with specific Navien products. The pump moves water; the heater still has to fire to reheat what comes back, so controls matter even more.
Is a recirculation pump a scald risk?
It can raise the risk, because hot water waits at every tap. CPSC says a 120°F water heater setting reduces the risk of most tap water scalds, and that 150°F water can burn badly in two seconds. Navien recommends thermostatic mixing valves at each point of use when the heater runs hot.
Does a recirculation pump need pipe insulation?
It should have it. Uninsulated hot pipe loses heat all along the loop. Washington’s residential energy code requires R-3 insulation on service hot water pipe, and the 2015 IECC requires R-3 on mechanical piping above 105°F. Check the edition your state adopted.
How long does it take a recirculation pump to bring hot water?
It depends on pipe length, pipe size and the pump’s flow. One residential model lists 1.32 gallons per minute at 15.4 feet of head. Demand systems are started a short time before use, so expect to press a button or trigger a sensor and wait briefly rather than get instant hot water at every moment.
Sources
- U.S. DOE Building America Solution Center (PNNL), Mechanical System Piping Insulation and Service Hot Water Systems Code Compliance (2015 IECC/IRC text), retrieved .
- Washington State Legislature, WAC 51-11R-40340, Section R403.5 Service hot water systems (Washington State Energy Code, Residential; versions effective until and from March 15, 2024), retrieved .
- Smart Energy Design Assistance Center, University of Illinois, Energy Code Smart Tip: Domestic Hot Water Recirculation (2018 IECC), retrieved .
- Dentz, Ansanelli, Henderson and Varshney (ARIES), Control Strategies to Reduce the Energy Consumption of Central Domestic Hot Water Systems, U.S. DOE Building America report DOE/GO-102016-4703 (June 2016), retrieved .
- Grundfos, COMFORT recirculation pumps product description (single manufacturer), retrieved .
- U.S. Consumer Product Safety Commission, Avoiding Tap Water Scalds (Document 5098), retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Code rules are quoted from the 2015 IECC/IRC text reproduced by the DOE Building America Solution Center, Washington’s adopted residential energy code (both the pre- and post-March 2024 versions) and SEDAC’s summary of the 2018 IECC.
Savings figures are from one DOE Building America field study in two multifamily buildings and are presented as such. Pump specifications, modes and safety advice come from single-manufacturer documents (Navien, Grundfos), labeled as such. Scald figures are from CPSC.
The model ICC code site was not readable at source, so model-code text is quoted only through these reproductions. No prices are given.
Suggest a correction. We fix errors and say what changed.