Comfort & Efficiency
Recirculation Pumps: Hot Water Faster Without Wasting It
A recirculation pump can cut a 90-second wait to five seconds. Run it wrong and it reintroduces exactly the standby loss the tankless unit was bought to eliminate. Here is how to get the first without the second.
11 min readUpdated
Quick Answer
Do I need a recirculation pump with a tankless water heater?
Only if the wait for hot water genuinely bothers you. A recirculation pump cuts a 60 to 120 second wait at distant fixtures down to a few seconds, but a continuously running pump reintroduces standby loss. Timer, on-demand or smart-learning control keeps the convenience without the waste. Frisco Tankless Water Heater Pros installs and configures recirculation at (972) 430-9024.
- Typical wait at a distant fixture without recirculation: 60-120 seconds
- Roughly 1.5 to 3 gallons of water go down the drain during that wait
- A dedicated return line is the best-performing configuration
- A crossover valve at the far fixture avoids opening walls but returns through the cold line
- Continuous operation can consume 20-40% of the efficiency gain tankless provided
- Installed cost in Frisco: roughly $400 to $1,800 depending on configuration
The problem recirculation solves, and the one it does not
Hot water does not travel instantly. When you open a tap, the water that comes out first is whatever was already sitting in the pipe, and it is at room temperature. Only after that volume has been flushed out does genuinely hot water arrive. In a two-story Frisco home with the water heater in the garage and the primary bathroom at the far end of the second floor, that can be sixty to a hundred and twenty seconds.
| Pipe size | Gallons per 10 ft | 40 ft run | 70 ft run |
|---|---|---|---|
| 1/2 inch | 0.10 gal | 0.4 gal | 0.7 gal |
| 3/4 inch | 0.23 gal | 0.9 gal | 1.6 gal |
| 1 inch | 0.41 gal | 1.6 gal | 2.9 gal |
Add the volume the fixture has to move at its own flow rate and the arithmetic explains the wait. A 2 GPM shower on a 70-foot three-quarter-inch run has to clear 1.6 gallons before hot water appears — about 48 seconds, before accounting for the pipe absorbing heat on the way.
How recirculation works
A recirculation system moves water from the hot line back to the water heater's inlet so that the pipe stays primed with hot water. When you open the tap, hot water is already at the fixture. The pump does the waiting instead of you.
- Dedicated return line
- A separate small-diameter pipe running from the furthest fixture back to the water heater's cold inlet, creating a closed loop. The best-performing configuration and the one that requires the most invasive installation.
- Crossover valve
- A thermostatic bypass installed under the sink at the furthest fixture, connecting hot to cold. It lets cooled hot water return through the existing cold line, eliminating the need for a new pipe — at the cost of briefly warming the cold water.
The four configurations
| Configuration | Installed cost | Wait time | Best for |
|---|---|---|---|
| Integrated pump with dedicated return | $900 - $1,800 | Under 10 seconds | New construction or an accessible-plumbing remodel |
| External pump with dedicated return | $700 - $1,500 | Under 10 seconds | Homes that already have a return line, often from an old tank system |
| Crossover valve with pump at the heater | $400 - $900 | 15 - 30 seconds | Retrofit where opening walls is not acceptable |
| Under-sink point-of-use pump | $300 - $600 | Under 10 seconds at that fixture only | One problem bathroom rather than a whole house |
In Frisco's existing housing stock, the crossover approach is by far the most common because a dedicated return means opening ceilings and walls. It works well. The trade-off is real but modest: the cold line at that fixture runs lukewarm for a short period after the pump cycles, which is mildly annoying at a bathroom sink and irrelevant elsewhere.
Control strategy is where the efficiency is won or lost
This is the part that gets skipped, and it is the part that determines whether recirculation is a smart addition or an expensive mistake. A pump circulating hot water through a loop twenty-four hours a day is heating pipe, insulation and framing continuously — which is functionally identical to the standby loss a storage tank has, and it is exactly what the tankless unit was bought to eliminate.
| Strategy | How it works | Efficiency impact | Convenience |
|---|---|---|---|
| Continuous | Pump runs 24/7 | Poor — can consume 20-40% of the efficiency gain | Perfect, always instant |
| Timer | Runs during set windows, e.g. 6-9am and 6-10pm | Good — loss confined to a few hours | Excellent within windows, normal outside them |
| Aquastat plus timer | Runs only within windows and only when loop temperature drops | Very good | Excellent within windows |
| On-demand button | Homeowner presses a button, pump runs one cycle | Best — near zero standing loss | Requires a few seconds of forethought |
| Motion or occupancy trigger | Sensor starts the pump when someone enters | Very good | Nearly invisible in use |
| Smart learning | Unit learns household patterns and pre-heats | Good, improves over weeks | Excellent once trained |
Our general recommendation for a Frisco household is an aquastat-controlled timer covering the two windows the household actually uses hot water in, plus an on-demand button in the primary bathroom for everything outside those windows. That combination captures nearly all of the convenience at a small fraction of the loss.
What it actually costs to run
There are two costs and people usually think about the wrong one. The pump's own electricity is trivial — a typical residential recirculation pump draws 25 to 60 watts, so even running continuously it costs a few dollars a month. The real cost is the gas the water heater burns to replace the heat the loop loses.
- Pump electricity, continuous operation: roughly $2 - $6 per month depending on the pump
- Heat loss from an uninsulated loop, continuous: often $10 - $25 per month in gas
- The same loop insulated: typically cuts that loss by 40-60%
- The same loop on a two-window timer: cuts it by roughly 75-85% versus continuous
- On-demand operation: reduces it to near zero, at the cost of pressing a button
The water savings argument, honestly assessed
Every wait for hot water sends water down the drain. A household waiting ninety seconds at 2 GPM wastes three gallons per event. Ten events a day is thirty gallons, or roughly 11,000 gallons a year.
That is a genuinely large volume and it is a legitimate reason to install recirculation, particularly under North Texas drought restrictions. But be clear-eyed about the economics: at typical Frisco water and sewer rates, 11,000 gallons is somewhere in the range of $60 to $120 a year. It does not repay a $1,200 installation quickly.
Recirculation is a comfort purchase with a water conservation benefit attached, and it is fine for it to be that. It is not an investment that pays for itself, and any pitch framing it that way is stretching.
Installing it correctly
Confirm the unit supports recirculation
Check the manual for minimum activation flow and whether an internal bypass or external sensing is required. Some units have recirculation logic built in and work best with the manufacturer's own pump.
Map the actual hot water branches
Identify which fixture is genuinely furthest by pipe path, not by floor plan. Placing the crossover valve at the wrong fixture leaves the real problem bathroom unaddressed.
Choose the return path
Dedicated return if the plumbing is accessible; crossover valve if not. Do not force a dedicated return through finished ceilings when a crossover gets you most of the benefit for half the cost.
Size the pump to the loop
An oversized pump moves water too fast for the exchanger to heat effectively and causes short-cycling. Loop length and pipe diameter determine the correct pump, and bigger is not better.
Insulate every accessible foot
Both supply and return. This is the cheapest efficiency measure in the entire installation and it is routinely skipped.
Configure the control before leaving
Timer windows matched to the household's real schedule, aquastat setpoint set, on-demand button located where it will actually be used. A pump left on the factory default is a half-finished job.
Measuring your actual wait before you spend anything
People consistently overestimate how long they wait for hot water, because waiting is annoying and annoyance distorts time. Before pricing a pump, spend ten minutes establishing the real numbers. This also tells you which fixture the system should be designed around, which is frequently not the one people assume.
Let the system rest first
No hot water use for at least two hours, so every branch has cooled to ambient. Testing right after a shower measures nothing useful.
Time each fixture individually
Open the hot side fully, start a timer, and stop when the water is genuinely hot rather than merely warm. Do the kitchen sink, every bathroom, and the laundry connection.
Note the flow rate too
A fixture with a low-flow aerator takes longer to clear the same pipe volume. A 90-second wait at a 0.5 GPM lavatory is a very different problem from a 90-second wait at a 2.5 GPM shower.
Repeat once in January conditions
Cold pipe running through an unconditioned attic or an exterior wall absorbs more heat from the leading edge of the hot water, so winter waits are genuinely longer. Design against the winter number.
| Measured wait | Interpretation | Recommendation |
|---|---|---|
| Under 20 seconds | Normal for the pipe run | Do nothing |
| 20 - 45 seconds | Noticeable but modest | Consider an under-sink point-of-use pump at the worst fixture |
| 45 - 90 seconds | Genuinely inconvenient daily | Crossover valve with timer control, or a dedicated return if accessible |
| Over 90 seconds | Long pipe run or oversized main | Dedicated return line if at all possible |
| Varies wildly between fixtures | Branch layout, not distance | Map the plumbing before choosing a configuration |
The tankless-specific downsides nobody mentions
- Increased throughput accelerates scaling — a recirculating system in Frisco's 8-11 grain water sees far more gallons across the exchanger, which can shorten the descaling interval to eight or ten months
- Short-cycling risk if the pump is oversized or the aquastat differential is too tight, which wears ignition components
- Some units cannot fire on the low flow a recirculation loop produces, requiring either a compatible pump or a small buffer tank
- Crossover valve installations warm the cold line at that fixture briefly after each cycle
- A pump is a moving part with a finite life — typically eight to twelve years — that the system did not previously have
- Continuous operation genuinely undermines the efficiency case for tankless, which is a real argument against doing it badly
Should you get one
The straightforward test is whether the wait actually bothers you. If your primary bathroom produces hot water in twenty seconds, recirculation is solving a problem you do not have. If it takes ninety seconds every morning and you have been running the tap while you brush your teeth for five years, it will change how the house feels.
- Worth it: waits over sixty seconds at fixtures you use daily
- Worth it: a large single-story footprint where pipe runs are long even without stairs
- Worth it: a household that values instant hot water and will accept a modest efficiency cost for it
- Worth it: doing it during a remodel when the walls are already open and a dedicated return is cheap
- Not worth it: waits under thirty seconds
- Not worth it: fixtures close to the heater that already perform well
- Not worth it: if the plan is to run it continuously — in that case you have traded away much of the reason you bought tankless
Frisco Tankless Water Heater Pros will measure the actual wait at each fixture, confirm what your specific unit supports, and configure the control strategy rather than leaving it on the factory default. Call (972) 430-9024.