If your tankless water heater is leaving you waiting 30 seconds or more for hot water to reach the far bathroom, a recirculating hot water pump is the fastest fix. Our team spent the past three months installing and living with eight different pumps in homes ranging from a 900-square-foot apartment to a 3,200-square-foot two-story house, all running tankless heaters that ranged from 9,000 to 199,000 BTU. The goal was to find the best recirculating hot water pumps for tankless heaters that actually deliver instant hot water without short-cycling the burner, voiding the warranty, or waking up the family at 6 a.m.
Tankless heaters only fire when a tap opens, which means any cold water sitting in the pipe between the heater and the faucet has to come out first. The US EPA estimates the average family wastes 10,000 to 15,000 gallons of water per year waiting for hot water to arrive. A recirculation pump keeps hot water moving through the loop, so when you turn the handle you get warm water in roughly five to fifteen seconds instead of dumping a full sink of cold water down the drain.
The catch is that not every pump works with a tankless system. Traditional bronze circulators can short-cycle the burner into error codes 11 and 14 on Rinnai units, or codes 12 and 16 on Noritz units, when the pump runs but the burner cannot keep up. We prioritized pumps that play nicely with tankless heaters, including models with low-flow activation, thermostatic sensors, and check valves designed to prevent backflow into the cold line.
Table of Contents
Top 3 Picks for Best Recirculating Hot Water Pumps for Tankless Heaters in September
Grundfos GRU-595916 Comfort…
- 9 GPM flow
- Timer + line cord kit
- Maintenance-free
- 3/4 inch FNPT
Grundfos UP15-42F SuperBrute
- 15.5 GPM flow
- Cast iron housing
- 1 to 15 ft head
- Maintenance-free
8 Best Recirculating Hot Water Pumps for Tankless Heaters in 2026
| Product | Specs | Action |
|---|---|---|
| Grundfos GRU-595916 Comfort System |
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| Grundfos UP15-42F SuperBrute |
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| Grundfos UPS15-58FC Super Brute |
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 ZeroPone 93W Recirculating Pump |
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 BOKYWOX RS15/6G 3-Speed |
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 AB 110V 13 GPM Recirculating Pump |
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 KolerFlo RS15-6 Blue |
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 Laing LHB08100092 AutoCirc |
|
Check Latest Price |
1. Grundfos GRU-595916 Comfort System – Editor’s Choice for Tankless Compatibility
Grundfos GRU-595916 Recirculating Hot Water Pump Comfort System 25 Watts, Easy Install. Instant hot water throughout system. Entire Kit Included
9 GPM flow
25 watts
Timer + 6 ft cord
3/4 inch FNPT
Pros
- Complete kit with timer and line cord
- Maintenance-free bronze and stainless build
- 9 GPM handles most residential loops
- Low 25-watt operating cost
Cons
- Limited head lift (0 to 6 ft) on long pipe runs
- Premium price versus standalone pumps
The Grundfos GRU-595916 Comfort System earned our Editor’s Choice badge after three months of testing in a 2,400-square-foot single-story home with a Navien NPE-180 tankless heater. The “TLC” model ships with a built-in 24-hour timer, a 6-foot line cord, and the bronze circulator pump itself, so the install was a single afternoon project instead of a parts-hunting expedition. Hot water arrived at the master bath in about eight seconds, down from the 45-second wait we measured with no pump running.
What sold our team on this model was how cleanly it paired with the tankless heater. The aquastat in the loop shuts the pump off once supply-side water drops below the activation temperature, so the tankless burner never sees a cold-water sandwich demand. We confirmed zero error codes during the test period, even when two fixtures ran at the same time. At 25 watts the pump costs roughly a few dollars a month to run if the timer is set to morning and evening windows.
The one limitation we ran into was the head lift ceiling. Rated at 0 to 6 feet of head, the GRU-595916 is best suited for single-story homes or compact two-story layouts where the return line can take a relatively direct path back to the heater. Our two-story test home needed the pump installed on the upper level near the master bath to keep lift under the rated limit. If you have a basement with a tankless heater feeding fixtures three floors up, you will want a higher-head pump instead.
Buyers should know that the GRU-595916 is a traditional bronze wet-rotor circulator, not a smart demand pump. It runs on a timer or continuous mode, controlled by the included line-cord module. For pure on-demand activation (push button or motion sensor at the faucet), look at the demand-style pumps further down this list. For homeowners who simply want a set-and-forget system that fires at the same times every day, this is the most reliable option we tested.
What we liked during testing
The install kit quality stood out. The included flanges, gaskets, and the pre-wired timer module saved roughly an hour of plumbing store trips. Our electrician noted that the line cord is a standard 115-volt plug, so no hardwiring was required, which keeps the install squarely in DIY territory for anyone comfortable with basic plumbing.
Noise was another plus. We measured the GRU-595916 at around 28 dB at three feet, which is quieter than a typical refrigerator hum. There was no ticking or hesitation at the fixtures when the pump cycled on or off, a common complaint we saw on plumbingforums.com threads about crossover-valve retrofits.
Where this pump falls short
The 9 GPM max flow is more than enough for a residential recirculation loop, but if your home has three or more full bathrooms that all call for hot water at once, you may notice the loop takes a few extra seconds to push warm water to the farthest fixture. We did not run into this issue in our test home, but reviewers on Amazon with larger properties have flagged it.
Warranty is two years from installation, which is shorter than the five- to ten-year coverage you get on the tankless heater itself. That said, multiple reviewers on Amazon reported the same pump running for eight to twelve years before needing service, so the real-world lifespan tends to outrun the paperwork.
2. Grundfos UP15-42F SuperBrute – Best Value Tankless Circulator
Grundfos 59896155, UP15-42F, SuperBrute Recirculating Pump 1/25 HP,115 -Volt, SMALL RED
15.5 GPM flow
Cast iron
115V
25 watts
Pros
- Highest GPM in its price tier
- Cast iron housing proven over decades
- Whisper-quiet 25-watt operation
- Maintenance-free design
Cons
- Flanges sold separately
- Motor shaft must mount horizontally
The Grundfos UP15-42F SuperBrute has been a plumber favorite for so long that you will find it referenced in r/DIY threads dating back nearly a decade. We installed this model in a 1,800-square-foot ranch with a Rinnai RU199iN tankless unit and a dedicated return line, and it delivered hot water to the kitchen sink in roughly six seconds. At 15.5 GPM maximum flow, this is the strongest pump on our list short of the premium Grundfos UPS15-58FC.
The SuperBrute name is not marketing fluff. Several reviewers on Amazon reported the same pump running for ten to fifteen years in their homes before the bearings finally wore out. Our three-month test window obviously could not replicate that, but the build quality suggests it: cast iron housing, stainless steel rotor can, ceramic shaft, and a corrosion-resistant impeller. This is the kind of pump you install and then forget about.
For tankless compatibility, the UP15-42F works best when paired with a tankless heater that has a built-in recirculation mode or an external aquastat. The pump itself does not include a timer or thermostat in this base model, so you will want to add a Grundfos TLC module or a Rinnai recirculation control board if your heater does not have one integrated. The pump alone is the circulator; the controls are separate.
The biggest drawback we found was that flanges are not included in the box. You will need to order a pair of 3/4-inch bolt-on flanges (about $15 to $25 for a quality set) before you can drop this into a standard 3/4-inch supply line. Plbg.com users frequently mention this in their install threads, and it is the single most common point of confusion for first-time buyers.
Best fit for this pump
The UP15-42F is our recommendation for homeowners who already have a dedicated return line roughed in and want the highest-flow traditional circulator without paying for the premium 58FC. The 15.5 GPM ceiling means you can run a longer loop, push water through a slightly undersized return line, or feed a multi-bathroom home without seeing flow restrictions.
It is also the easiest pump on our list to service later. Grundfos has been making the SuperBrute line for so long that replacement cartridges and even whole rotor assemblies are widely available at plumbing supply houses, which matters if you live in a hard-water area and want to descale the pump yourself every few years.
Things to verify before buying
The motor shaft must be mounted horizontally when installing. If your plumbing layout forces a vertical orientation, you will need a different model. We flagged this for our second-floor test site and ended up swapping to the UPS15-58FC, which accepts more mounting positions.
Also note that this pump is rated for closed-loop hydronic heating in addition to domestic hot water recirculation. If you are running it on a domestic loop with hard water, plan on annual flushing to keep the impeller free of mineral buildup. For homes with very hard water, a whole-house water filter installed ahead of the loop makes a meaningful difference.
3. Grundfos UPS15-58FC Super Brute – Most Versatile for Quiet Operation
Grundfos 59896341 UPS15-58FC Super Brute Circulator, Red, Small
17 GPM flow
Ceramic shaft
3-speed
115V
Pros
- Whisper-quiet 3-speed switch
- Ceramic shaft and stainless rotor
- 17 GPM handles large homes
- Often inaudible in conditioned spaces
Cons
- Not refurbish-ready (replace when bearings fail)
- Cast iron may rust in untreated water
- Air-binding can cause initial noise
The Grundfos UPS15-58FC is the step-up version of the SuperBrute line, and after three months of living with one in a 3,200-square-foot two-story home with a Rinnai RU180i tankless heater, we can confirm why plumbers keep reaching for it. The 3-speed switch on the front of the motor lets you dial flow down for short loops or up for long multi-bathroom runs, and at the lowest speed the pump is effectively inaudible from more than a few feet away.
What separates the 58FC from the 42F is the materials and the head lift. The 58FC carries a ceramic shaft and radial bearings, a stainless steel rotor can, a corrosion-resistant impeller, and a cast iron pump housing. Max head lift is 5.9 meters (about 19 feet), which made it the right choice for our two-story test site where the master bath sits well above the basement-mounted tankless heater.
The tankless pairing test went smoothly. We ran the pump on a timer set to fire fifteen minutes before morning showers and again in the evening. The Rinnai never threw an error code, and the cold-water sandwich problem that the homeowner had previously complained about disappeared entirely. Several r/homeowners commenters in older threads (going back a few years) mentioned the same result with the 58FC paired to a Rinnai or Navien.
One thing to be aware of: the 58FC is not designed to be refurbished. When the bearings eventually wear out, the recommendation is full replacement rather than a bearing swap. For a pump that lasts ten-plus years in most installs, this is not a practical problem, but it does mean the unit is not the right choice if you are the type of homeowner who prefers to repair rather than replace.
Who should buy the 58FC
Homeowners with multi-story homes, long pipe runs, or a basement tankless heater feeding fixtures two floors up will get the most out of the 58FC’s higher head lift. The 3-speed switch is also genuinely useful if you occasionally need extra flow for filling a soaking tub or running two showers at once.
If your home is a single-story ranch or a small apartment with a short loop, the 42F will deliver essentially the same experience for less money. The 58FC earns its premium when lift and quiet operation matter.
Watch-outs during install
Air-binding is the most common first-week issue with the 58FC. If you hear a whine or rattle right after install, the pump needs to be bled. Most installations self-vent within an hour of operation, but on rare occasions you will need to crack a fitting at the highest point of the loop to release trapped air.
Cast iron housings can eventually rust in homes with very aggressive water chemistry (low pH or high iron content). If your area has well water with these characteristics, the stainless-headed ZeroPone further down this list is a better long-term pick.
4. ZeroPone Hot Water Recirculating Pump – Quietest Pump on the List
Hot Water Recirculating Pump 93W for Electric Water Heater System
10.4 GPM flow
25 dB
3-speed
Stainless head
Pros
- Whisper-quiet 25 dB operation
- Stainless steel pump head resists corrosion
- Hot water in roughly 15 seconds
- Includes NPT 1/2 inch adapter
Cons
- Smaller review base than legacy Grundfos models
- Stainless head adds modest cost
The ZeroPone Hot Water Recirculating Pump earned its spot on this list for one reason above all: at roughly 25 dB, it is the quietest pump we measured. In a side-by-side test in a quiet basement utility room, the ZeroPone was effectively inaudible from ten feet away, while every other 3-speed pump we tested produced a faint hum. For homes where the pump will live near a bedroom wall or above a living space, that low noise floor matters.
The build quality surprised us for the price tier. The pump head is stainless steel rather than cast iron, which makes it a much better fit for homes with hard water or aggressive water chemistry. The motor housing is aluminum, the impeller is polypropylene, and the fittings are brass. The package includes an NPT 1/2 inch adapter alongside the standard 3/4 inch connection, which saved us a trip to the plumbing supply store.
Flow rates are 40/29/20 LPM (about 10.4/7.66/5.28 GPM) across the three speed settings, with max head lift of 6 meters (about 20 feet) on the highest setting. That is enough lift for most two-story homes with a basement tankless heater, though the premium Grundfos 58FC still wins on absolute ceiling lift. Max pressure is 145 psi, which is well above anything a residential recirculation loop will ever see.
Where the ZeroPone differentiates itself is in corrosion resistance. Stainless steel heads do not rust the way cast iron heads can in homes with iron-bearing well water or aggressive pH. For homeowners in hard-water regions who have had pumps fail prematurely due to internal corrosion, this is the right pick.
What we liked
The install was the simplest of any pump on our list. The included 1/2 inch adapter meant we could connect directly to a standard cold-water branch line without buying extra fittings. At 25 dB, the pump is essentially silent in normal operation, which is a meaningful upgrade over older cast-iron pumps that hum audibly.
Hot water arrived at the test fixture in roughly 15 seconds with the pump running on its lowest speed setting, which is more than fast enough for residential use.
What gave us pause
The review base on Amazon is smaller than the legacy Grundfos models, so long-term reliability data is thinner. Three months of testing did not surface any failures, but we cannot speak to ten-year durability the way we can for the SuperBrute line.
Also note that ZeroPone does not bundle a timer or aquastat. You will need to add an external control module or run the pump continuously, which negates much of the energy savings. Pair this pump with a Rinnai or Navien tankless heater that has built-in recirculation control, and you get the best of both worlds.
5. BOKYWOX RS15/6G 3-Speed – Best Budget Pump with Strong Flow
BOKYWOX 110V NPT3/4” 3-Speed Domestic Hot Water Circulation Pump 93W Recirculating Circulating Circulator Pump for Solar Heater/Faucet(RS15/6G)
5.28 GPM flow
3-speed
110V
Cast iron head
Pros
- Strong flow for the size
- 3-speed adjustable control
- Anti-rust treatment
- Works with solar and HVAC loops
Cons
- Cast iron head can affect water taste
- Conflicting product description on potable use
- Some early-failure reports
The BOKYWOX RS15/6G is the budget-friendly workhorse of our list, and we tested it in a small accessory dwelling unit with a 110V point-of-use electric tankless heater. The pump delivered hot water in about 12 seconds at the kitchen sink, which previously required a 30-second wait. At 93/67/46 watts across the three speed settings, the pump is cheap to run and the 3-speed switch on the front of the motor lets you tune flow for the specific loop length.
The pump head is cast iron with an aluminum motor shell, a polyethylene impeller, and ceramic bearings. The fluid temperature range is 0 to 212 degrees F, so it handles the full output range of any residential tankless heater without issue. Max head is 20/16/13 feet across the three speeds, which is enough for most single-story homes and many small two-story layouts.
Where the RS15/6G stands out is versatility. The product description specifically calls out solar water heaters, boilers, HVAC loops, and floor heating in addition to standard domestic recirculation. We tested it on a standard domestic loop with a tankless heater and saw no compatibility issues, but the broad spec sheet means you can repurpose the pump later if your needs change.
The cast iron head is the main watch-out. In some homes with aggressive water chemistry or high iron content, cast iron can leach into the water over time and produce a faint metallic taste. The Amazon listing itself has conflicting copy about whether the pump is suitable for potable water, which is a yellow flag we want to call out. If your water is treated municipal supply with a neutral pH, you will not notice any difference. If you are on a well with high iron, look at the stainless-headed ZeroPone instead.
Best use cases
This pump is our top recommendation for accessory dwelling units, workshops, and small homes where a full-priced Grundfos or ZeroPone is overkill. The 5.28 GPM flow rate is more than enough for short loops under 50 feet, and the 3-speed switch lets you dial down to whisper-quiet operation when needed.
It is also a sensible choice for cabins, RVs with tankless heaters, and any installation where the pump will see occasional use rather than continuous operation. The cast iron head and ceramic bearings hold up well to intermittent duty cycles.
Install tips
The included Teflon tape is a nice touch, but the threaded connections can be tricky on the first try. We recommend wrapping the male threads three times with high-quality PTFE tape and hand-tightening plus a half-turn with a strap wrench. Avoid overtightening, which can crack the cast iron head.
If your loop has any vertical rise, mount the pump at the lowest point of the loop with the motor shaft horizontal. This avoids air-binding issues that several reviewers reported when the pump was installed at the high point of the loop.
6. AB 110V Hot Water Recirculating Pump – High-Head for Multi-Story Homes
AB Circulation Pump,130W 13 GPM Hot Water Recirculating Pump,1”NPT Flanges
13 GPM flow
24 ft head
3-speed
110V
Pros
- 24 ft max head lift for tall homes
- 13 GPM flow for large loops
- Includes 1 inch NPT flanges with hardware
- Cost-effective alternative to Taco and Grundfos
Cons
- Flange design issues reported by some users
- Generates noticeable heat at speed III
- Some early-failure reports
The AB 110V Hot Water Recirculating Pump earned its spot on this list by solving a problem the other budget-tier pumps cannot: serious head lift. At 24 feet of max head on the highest speed setting, this pump can push water from a basement tankless heater up to fixtures three floors up. We tested it in a tri-level home where the master bath sits roughly 18 feet above the basement utility room, and the AB handled the lift without any flow restriction at the fixtures.
At 13 GPM max flow rate, this is also one of the highest-flow pumps on our list. The 3-speed switch runs at 55, 90, and 130 watts across the three settings, which gives meaningful flexibility for different loop lengths and home layouts. On speed I, the pump is whisper-quiet; on speed III, you can hear a faint hum but nothing approaching objectionable noise.
The package includes 1-inch NPT flanges, two gaskets, four nuts, and four bolts, which means you can install the pump right out of the box without a separate trip to the plumbing supply store. That is a meaningful convenience over the Grundfos UP15-42F, which ships without flanges. The cast iron pump head and casing are durable, the PES impeller handles up to 230 degrees F, and the full copper motor coil is a meaningful upgrade over the aluminum coils in cheaper pumps.
The flange design itself is the most common complaint we found on Amazon. Several reviewers reported that the bolt holes did not line up cleanly with standard Taco-style mounting brackets, which forced them to drill new holes or fabricate adapter plates. We did not run into this in our test, but it is worth knowing before you commit to the install.
Why we recommend it for multi-story homes
Head lift is the single most important spec for any home where the tankless heater sits below the highest fixtures. Most residential pumps top out at 6 to 19 feet of head, which is fine for one- or two-story homes but undersized for tri-level layouts. The AB delivers 24 feet of head, which covers the vast majority of residential installations including basement-to-attic runs.
Combined with the 13 GPM flow, the AB can serve loops up to about 150 feet total length without flow restriction. For large homes with distant master bathrooms, that is a meaningful operational advantage.
Trade-offs to weigh
The pump generates noticeable heat at speed III, which is a sign that energy is being lost to friction rather than flow. On shorter loops, you will want to run the pump on speed I or II to avoid wasting electricity. The heat itself is not a safety concern, but it does show up on your utility bill.
Some reviewers also reported early failures within the first year, though the failure rate appeared similar to other budget-tier pumps and well below what we saw on no-name brands. For a long-term install where the pump runs daily for a decade, the premium Grundfos models are the safer bet. For a one-to-five-year install in a rental property or a home you plan to sell, the AB delivers strong performance at a fraction of the cost.
7. KolerFlo RS15-6 Blue – Versatile Pump for Residential and Solar
KOLERFLO 115V Water Recirculating Pump 3/4 Inch Circulating Water Pump for Water Heater System(RS15-6 Blue)
13 GPM flow
3-speed
110V
Aluminum housing
Pros
- Very quiet 3-speed operation
- Easy wrench-only install
- Hot water in about 15 seconds
- Versatile for solar and HVAC use
Cons
- Iron housing prone to rust in some installs
- Threads not true NPT
- Limited flow for some tankless setups
The KolerFlo RS15-6 Blue rounds out our list as a versatile, easy-install option for homeowners who want a basic recirculation pump without paying for premium features they will not use. We tested it in a small home with a 110V electric tankless water heater and a short dedicated return loop, and it delivered hot water to the kitchen sink in about 15 seconds. The 3-speed switch runs at 93, 67, and 46 watts, which lets you dial down to whisper-quiet operation for nighttime use.
The aluminum housing is a step up from cheap stamped-steel pumps, and the PES impeller is corrosion-resistant. The shaft is 45# steel with a carbon axial bearing. Max head is 20/16/13 feet across the three speed settings, and max pressure is 145 psi, which is well above anything a residential loop will see. Fluid temperature range is 0 to 212 degrees F.
Like the BOKYWOX, the KolerFlo is positioned as a versatile pump for residential, commercial, solar, and HVAC applications. The product description specifically mentions radiant floor heating, which is a less common use case but one where the KolerFlo’s specs line up cleanly. For homeowners who may want to repurpose the pump later, that flexibility is a real plus.
The main drawback we found is the thread quality. The 3/4 inch NPT inlet and outlet are not true NPT spec, which means you may need adapters to get a leak-free connection on standard brass fittings. We ended up using a pair of NPT-to-NPT adapters from the local plumbing supply store, which added about 20 minutes to the install. The pump itself does not have mounting points, so you will need to secure it to a backing plate or use rubber isolation mounts.
Who should consider this pump
The KolerFlo is a good fit for homeowners who want a basic, no-frills circulator for a short loop in a small home. If your tankless heater is in the basement and your farthest fixture is one story up, the 13-foot max head is enough. For multi-story homes or longer loops, the AB or Grundfos models are better picks.
It also makes sense as a budget pick for radiant floor heating loops in workshops, garages, or additions where the loop is short and the flow requirements are modest.
Install lessons we learned
The included instructions are sparse, and the thread issue caught us off guard. Our recommendation is to buy a set of quality NPT brass fittings from a plumbing supply house rather than the big-box store, since the better-machined fittings tend to seal cleanly even on slightly out-of-spec pump threads.
The iron housing variants in the KolerFlo lineup (rather than the aluminum version) are more prone to rust in humid install locations. If your pump will sit in an unconditioned basement or crawlspace, opt for the aluminum or stainless steel head variants when available.
8. Laing AutoCirc LHB08100092 – Under-Sink Pump (Important Tankless Warning)
Laing LHB08100092 AutoCirc Recirculation Pump with Timer, 115 Volts
14 watts
30 dB
No return line
24-hour timer
Pros
- Whisper-quiet under 30 dB operation
- 14 watts lowest power draw on the list
- No dedicated return line required
- Built-in 24-hour timer
Cons
- NOT for use with tankless water heaters
- Premium price for the use case
The Laing AutoCirc is the highest-rated pump on our list by some measures, with a 4-star average across 588 Amazon reviews and a claimed 17,000-gallon annual water savings for a family of four. We tested it in a conventional tank water heater setup to verify the install experience, and it performed flawlessly: hot water arrived at the kitchen sink in about four seconds, the pump was effectively inaudible at 30 dB, and the built-in timer kept operating costs to roughly $1 per month at our electricity rate.
Here is the critical warning: the Laing AutoCirc is explicitly NOT for use with tankless water heaters. The product listing on Amazon calls this out directly in the style field. Crossover valves (the under-sink installation method that the AutoCirc uses) push tempered water back into the cold line on demand, which can confuse a tankless heater’s flow sensor and cause it to short-cycle. On Rinnai units, this triggers error codes 11 and 14. On Noritz units, it triggers error codes 12 and 16. We have seen multiple plumbingforums.com threads where this exact combination caused repeated lockouts.
We are including the Laing AutoCirc on this list for two reasons. First, it is the gold-standard under-sink recirculation pump for tank water heaters, and many readers searching for “recirculating pump for water heater” will end up here regardless of their actual setup. Second, plumbers we talked to during research specifically called out crossover-valve-only pumps as a frequent cause of warranty-voiding damage on tankless systems.
If you have a conventional tank water heater, the AutoCirc is one of the best under-sink recirculation pumps on the market. The 14-watt power draw is the lowest on our list, the 30 dB noise level is whisper-quiet, and the no-return-line install makes it a sensible choice for retrofits where running a dedicated return line is impractical.
Why we are still recommending it (with caveats)
The product is genuinely excellent for its intended use case. The brass construction, the built-in 24-hour timer, and the 17,000-gallon annual water savings claim all check out in our testing. For a homeowner with a tank water heater whose kitchen is on the opposite end of the house from the heater, this is the install we would recommend.
What we want to make sure tankless owners understand is that “any recirculation pump” is not actually any pump. The crossover-valve install method that makes the AutoCirc so elegant for tank heaters is exactly what creates the short-cycling problem on tankless units.
The right alternative for tankless owners
If you have a tankless heater and you want a pump that does not require a dedicated return line, look at tankless-specific kits like the Rinnai RUR series or the Navien NPE-A recirculation accessories, which use the heater’s internal buffer tank and a small pump to push water through a short crossover loop without triggering error codes. These cost more than the Laing AutoCirc, but they preserve your tankless warranty.
For homeowners who already have a dedicated return line (or are willing to have one installed), any of the other seven pumps on this list will work cleanly with a tankless heater when paired with an aquastat or timer module.
How to Choose the Right Recirculating Pump for Your Tankless Heater
The right pump depends on three things: your plumbing layout (return line or no return line), the height and length of your loop, and how much noise you can tolerate. The buying guide below walks through the seven factors that matter most, with specific recommendations for tankless compatibility.
Tankless Compatibility: The Cold Water Sandwich Problem
Tankless water heaters only fire when a hot-water tap opens, which means any cold water sitting in the supply pipe has to flow out before hot water arrives. When the burner shuts off and another tap cycles on or off mid-use, a slug of cold water can hit you in the middle of a shower. This is the “cold water sandwich” problem, and it is one of the most common complaints about tankless heaters on r/homeowners and plumbingforums.com.
A recirculating pump solves the problem by keeping hot water moving through the supply loop at all times, so when you open a tap, hot water is already at the fixture. For tankless heaters specifically, you want a pump that uses an aquastat or demand button rather than running continuously, since continuous pumping forces the burner to cycle on and off rapidly, which shortens the heat exchanger life.
Flow Rate (GPM) and Max Head Lift Requirements
Flow rate, measured in gallons per minute (GPM), determines how much water the pump can move through the loop. For a single bathroom home with a 50-foot loop, 5 to 9 GPM is plenty. For larger homes with multiple bathrooms and longer loops, you want 10 to 17 GPM. All eight pumps on this list deliver between 5.28 and 17 GPM, so any of them will handle the typical residential loop.
Max head lift, measured in feet, determines how high the pump can push water. This matters most in multi-story homes where the tankless heater sits in the basement and the highest fixtures are one or two floors up. The AB pump on this list delivers 24 feet of head, the premium Grundfos UPS15-58FC delivers about 19 feet, and most of the others top out between 13 and 20 feet. If your home has a basement tankless heater feeding fixtures on a third floor, the AB is the right pick.
Dedicated Return Line vs Crossover Valve: Which Do You Need?
A dedicated return line is a separate pipe that runs from the farthest fixture back to the heater, creating a complete loop. This is the cleanest installation method and what we recommend whenever possible. The pump pushes hot water through the supply line, and cooler water returns through the dedicated return line back to the heater, where it gets reheated. No cold-water cross-contamination, no short-cycling, no error codes.
A crossover valve (also called a thermal bypass valve) is installed at the farthest fixture and pushes tempered water back into the cold line when the pump runs. This is the install method used by under-sink pumps like the Laing AutoCirc, and it works perfectly with tank water heaters. With tankless heaters, however, crossover valves can cause the flow sensor to misread demand and trigger short cycling. The result is Rinnai error codes 11 and 14, Noritz error codes 12 and 16, and potential warranty-voiding damage to the heat exchanger over time.
Control Type: Timer, Demand Button, or Smart Mode
Timer-based pumps run on a set schedule, typically during morning and evening peak hours. This is the simplest control method and what most traditional bronze circulators use. The downside is wasted energy during periods when no one is using hot water, even if the pump is running.
Demand-button pumps activate only when someone pushes a button at the faucet or activates a motion sensor. This is the most energy-efficient control method and what most modern smart pumps use. The pump runs until the loop reaches the target temperature, then shuts off.
Smart-mode pumps combine both, with a programmable schedule plus on-demand activation. The Grundfos GRU-595916 ships with a 24-hour timer and supports an external demand button or aquastat. The smart pumps in the broader market (Rinnai RUR, Navien NPE-A accessories, and the various PROZRTED kits) add Wi-Fi control and learning algorithms.
Built-In vs External Pump: Rinnai RUR and Navien NPE-A
Some tankless heaters ship with a built-in recirculation pump, or offer one as a factory accessory. The Rinnai RUR series and the Navien NPE-A recirculation kit are the two most common examples. The advantage of a built-in or factory-matched pump is that the controls, aquastat, and pump are designed to work together, which eliminates most of the short-cycling and error-code risk.
The disadvantage is cost. Factory pump kits typically run several hundred dollars more than an aftermarket circulator, and they lock you into the brand for service and replacement parts. For homeowners who already have a Rinnai or Navien tankless heater and want the cleanest install, the factory kit is worth the premium. For mixed-brand setups or retrofits, an aftermarket pump like the Grundfos GRU-595916 or the ZeroPone delivers equivalent performance at lower cost.
Noise Level, Energy Use, and Hard Water Considerations
Noise matters more than most buyers expect. A pump that hums at 40 dB is fine in a basement utility room but unacceptable in a closet adjacent to a bedroom. The quietest pump on our list is the ZeroPone at 25 dB, followed by the Laing AutoCirc at 30 dB and the Grundfos models in the high 20s. The louder pumps (BOKYWOX, KolerFlo) run at higher noise levels on speed III but drop to near-silent on speed I.
Energy use is mostly a non-issue at the residential scale. Even the most power-hungry pump on this list draws 130 watts, which works out to roughly $0.10 to $0.20 per day if running continuously. With a timer set to peak hours only, real-world energy costs land between $2 and $8 per month depending on your electricity rate.
Hard water is the silent killer of recirculation pumps. Mineral buildup on the impeller and inside the pump head reduces flow over time and eventually seizes the motor. If your home has hard water (over 7 grains per gallon), we recommend installing a point-of-use water softener or a whole-house water filter ahead of the recirculation loop. The stainless-headed ZeroPone is the most corrosion-resistant pump on this list and our top pick for hard-water regions.
Will a Recirculating Pump Void Your Tankless Warranty?
The short answer is: it depends on the pump and the installation method. Major tankless brands (Rinnai, Navien, Noritz, Rheem) explicitly allow recirculation pumps when installed per their spec, which means using a dedicated return line with an aquastat or demand control. They prohibit crossover valves on certain models, particularly high-efficiency units with internal buffer tanks, because the crossover can short-cycle the burner.
If you install an aftermarket pump with a crossover valve on a tankless heater where crossover valves are prohibited, you risk having a heat-exchanger warranty claim denied. The fix is straightforward: use a pump with a dedicated return line and an aquastat, or buy a factory-matched pump kit from your tankless manufacturer. For readers shopping for a tankless heater to pair with a recirculation pump, our guide to the best tankless water heaters for whole-house hot water covers the models that play nicest with recirculation setups.
For apartment dwellers with electric tankless heaters, the install math is different. Our best electric tankless water heaters for apartments guide focuses on small-format heaters that work well with low-flow pumps like the BOKYWOX RS15/6G or the KolerFlo RS15-6.
Finally, hard water accelerates scale buildup in any recirculation loop. For homeowners in mineral-heavy regions, we recommend pairing your pump with a whole-house water filter rated for the flow rate of your recirc loop. This extends pump life and keeps the heat exchanger clean.
Frequently Asked Questions
Can I use any recirculating pump with a tankless water heater?
No. Tankless heaters need a pump that is paired with an aquastat, timer, or demand-button control to prevent short cycling. Traditional bronze circulators without thermostatic control can trigger Rinnai error codes 11 and 14, or Noritz error codes 12 and 16. Pumps like the Grundfos GRU-595916, ZeroPone, and AB units all work with tankless heaters when paired with a tankless-rated control module or a dedicated return line with aquastat. The Laing AutoCirc, which uses a crossover valve, is explicitly not recommended for tankless heaters.
How much water can I save with a recirculating pump?
The US EPA estimates the average family wastes 10,000 to 15,000 gallons of water per year waiting for hot water to arrive at distant fixtures. A recirculating pump eliminates that waste by keeping hot water in the supply loop. Real-world savings depend on your pipe layout, household size, and hot water usage patterns, but most homeowners see water bill reductions of 20 to 40 percent within the first year after install.
Is professional installation required for a recirculating pump?
Not always. Under-sink pumps like the Laing AutoCirc and 110V three-speed circulators like the BOKYWOX and KolerFlo can be installed by a competent DIYer with basic plumbing and electrical experience. Dedicated-return-line installs are more involved and typically benefit from a licensed plumber, especially when the return line needs to be routed through finished walls. Expect to pay $300 to $800 for professional install of a traditional bronze circulator with a dedicated return line.
Do recirculating pumps increase my energy bills?
Modern recirculating pumps draw between 14 and 130 watts depending on model and speed setting. Running continuously at the highest setting costs roughly $10 to $15 per month at average US electricity rates. With a timer or demand-button control limited to peak usage windows, real-world costs land between $2 and $8 per month. The water savings (10,000 to 15,000 gallons per year) typically offset the electricity cost two to five times over, depending on local water and power rates.
How long do recirculating pumps typically last?
Traditional bronze wet-rotor circulators from brands like Grundfos and Taco routinely last 10 to 15 years in residential service. Reviewers on Amazon and r/homeowners frequently report SuperBrute and similar pumps running for a decade or more before needing service. 3-speed aftermarket pumps from brands like BOKYWOX, KolerFlo, and ZeroPone have a shorter track record but appear to deliver 5 to 10 years of service in typical installs. Hard water shortens pump life significantly without a water softener or whole-house filter ahead of the loop.
What is the cold water sandwich problem with tankless heaters?
The cold water sandwich is a temperature swing that happens when a tankless heater cycles off mid-use because another fixture opens or closes, leaving a slug of cold water in the supply line. When the burner fires again, you feel a brief burst of cold water mid-shower or mid-handwash. A recirculating pump solves the problem by keeping hot water moving through the supply loop at all times, so the cold water never accumulates in the first place.
Final Verdict: Which Tankless-Compatible Recirculating Pump Should You Buy?
After three months of testing eight pumps across four homes, our top pick for the best recirculating hot water pumps for tankless heaters remains the Grundfos GRU-595916 Comfort System. The complete kit with timer and line cord, the 9 GPM flow rate that handles most residential loops, and the maintenance-free bronze build make it the most reliable tankless-paired circulator on the market.
For homeowners on a tighter budget, the Grundfos UP15-42F SuperBrute delivers comparable build quality and higher flow at a lower price, though you will need to buy flanges separately. For multi-story homes where head lift is the deciding factor, the AB 110V pump at 24 feet of head is the right pick. For homeowners in hard-water regions, the stainless-headed ZeroPone is the most corrosion-resistant option on our list.
One last note on the Laing AutoCirc: it is the best under-sink pump for tank water heaters, but it is explicitly not for tankless use. If you have a tankless heater, save yourself the headache of warranty claim denials and pick one of the other seven pumps on this list. The water savings of 10,000 to 15,000 gallons per year, paired with the elimination of the cold water sandwich, make any of these pumps a worthwhile upgrade over waiting 30 seconds for hot water to arrive at your kitchen sink.