A hot water recirculating pump delivers hot water to your faucets in 2–5 seconds instead of 30–60 seconds, by keeping hot water circulating through your pipes or by sending cooled water in the hot line back to the heater. A basic demand pump costs $200–$400 installed and saves 3,000–8,000 gallons of wasted water per year while adding $20–$60 annually in energy cost.
For tankless water heater owners, a recirculating pump solves the biggest complaint: the delay between opening a faucet and getting hot water. Here is how every type works, what they cost, and which integrates best with tankless systems.
How Recirculating Pumps Work
Without a recirculating pump, hot water sits in your pipes after you close a faucet. It cools to room temperature within 20–45 minutes. The next time you open a faucet, you wait while cold water in the pipe is pushed out and replaced by fresh hot water from the heater. In a typical home with 30–50 feet of pipe between the heater and the farthest faucet, that wait is 15–45 seconds.
A recirculating pump moves water through the system so hot water is always near the faucet. There are three main approaches:
1. Dedicated Return Line System (Full Loop)
A dedicated hot water return line runs from the farthest fixture back to the water heater. A small pump (typically 1/25 HP, 10–25 watts) sits at the heater and continuously or intermittently circulates water through this loop.
Pros: Fastest hot water delivery (2–3 seconds). No cross-contamination between hot and cold lines. Most consistent temperature.
Cons: Requires a dedicated return pipe — easy in new construction, expensive to retrofit ($1,000–$3,000 to run a new pipe through finished walls). Higher energy use from continuous circulation.
2. Comfort Valve / Crossover System (Retrofit-Friendly)
A thermostatic crossover valve is installed under the farthest sink. A pump at the heater pushes hot water through the hot line; when the water reaches the crossover valve, it opens and sends cooled water back through the cold water line to the heater. No dedicated return pipe needed.
Pros: No new piping — uses existing hot and cold lines. Easy retrofit ($200–$500 installed). Works with any water heater.
Cons: Momentarily warms the cold water line (cold water may be lukewarm for 10–30 seconds after the pump cycles). Slightly slower than a dedicated loop.
3. Demand Pump (Push Button / Motion Sensor)
A pump activates only when you press a button, trigger a motion sensor, or use a smart home signal. It pushes hot water to the fixture and stops when hot water arrives (sensed by a temperature switch). No wasted energy circulating when nobody needs hot water.
Pros: Zero standby energy waste. No warming of cold lines during idle periods. Available in both dedicated-line and crossover configurations.
Cons: Requires a 3–10 second wait after pressing the button. Needs a button or sensor at each fixture (or a central smart home trigger).
Recirculating Pump Types Compared
Recirculating Pumps With Tankless Water Heaters
Tankless heaters add a wrinkle: they have a minimum activation flow rate (typically 0.4–0.75 GPM). If the recirculating pump's flow rate falls below this threshold, the tankless unit will not fire, and the pump circulates cold water uselessly.
Dedicated Return Line + Tankless
This is the gold standard. The pump pushes water through the loop at 1–3 GPM, exceeding the tankless minimum flow rate. The tankless fires, heats the water, and hot water reaches every fixture in seconds.
Critical requirement: The pump flow rate must exceed the tankless minimum activation rate. Most recirc pumps deliver 0.5–3.0 GPM, which works for most tankless models. Verify your specific unit's minimum flow spec.
Crossover Valve + Tankless
This works but has a caveat. The crossover valve sends cooled water from the hot line back through the cold line. When the pump activates and the tankless fires, the cold line temporarily carries warm water. Once hot water reaches the valve, the thermostatic element closes and the pump stops.
Compatibility check: Some older tankless models struggle with the low flow rates of crossover systems. Modern units from Navien, Rinnai, and Noritz with 0.4 GPM minimum activation rates work well.
Built-In Recirculation (Navien, Rinnai, Rheem)
Several tankless manufacturers now build recirculation directly into the unit:
Navien's ComfortFlow is the best integrated solution. It includes a small buffer tank that eliminates the cold-water sandwich effect and a built-in pump that works with or without a dedicated return line. The NaviLink app learns your usage patterns and pre-heats the loop before your typical morning shower time. No aftermarket pump needed.
How Much Water Does a Recirc Pump Save?
Every second of waiting for hot water wastes approximately 0.03–0.05 gallons (at a typical 2.0 GPM faucet, including the initial slow-flow startup). A 30-second wait wastes about 0.5–1.0 gallons per event.
For a family of 4 with 15–25 hot water events per day:
The water savings alone rarely justify the pump's cost. The real value is convenience: instant hot water without standing at the faucet watching cold water run down the drain.
Energy Cost of Recirculation
Recirculating hot water through pipes means heat loss through those pipes. Even insulated pipes lose heat. This additional energy cost must be factored in:
Continuous circulation: The heater fires more frequently to maintain loop temperature. Additional energy: 500–2,000 kWh/year (electric) or 30–80 therms/year (gas). Annual cost: $50–$300 depending on fuel and insulation.
Timer-based circulation: Limits circulation to peak usage hours (6–8 AM, 5–8 PM). Reduces additional energy to 200–800 kWh/year or 12–30 therms/year. Annual cost: $20–$120.
Demand-based circulation: Only runs when triggered. Minimal pipe heat loss because water only circulates for 30–60 seconds per event. Additional energy: 50–200 kWh/year or 3–10 therms/year. Annual cost: $5–$30.
Continuous recirculation with a tankless heater can increase energy costs by $100–$300/year, partially negating the tankless efficiency advantage. For tankless systems, demand or timer-based pumps are strongly recommended over continuous operation.
Top Recirculating Pump Models (2026)
Grundfos Comfort PM — Best Overall
The Comfort PM is the most versatile option. It installs at the water heater (dedicated loop) or under a fixture (crossover), runs on demand via a push button or motion sensor, and includes a programmable timer for scheduled circulation. At 15 watts, it is the most efficient continuous-capable pump available. Stainless steel construction resists corrosion.
Watts 500800 — Best Budget Crossover
The Watts Premier kit includes the pump, crossover valve, timer, and all fittings for under $280. It installs under the farthest sink in 30–60 minutes without new piping. The timer limits circulation to programmed hours. This is the most popular retrofit solution in the U.S.
Real-World Examples
Example 1: New Build With Navien NPE-2
Setup: 2,800 sq ft home, Navien NPE-2 240S with ComfortFlow. Dedicated return line installed during construction ($600 for the pipe run).
Result: Hot water at every fixture in 2–3 seconds. NaviLink app schedules recirculation from 6–9 AM and 5–9 PM. Monthly energy increase from recirculation: approximately $12. Zero water wasted. The family never thinks about hot water timing.
Example 2: Retrofit Crossover With Rinnai
Setup: 1,900 sq ft existing home with Rinnai RU160iN. Watts 500800 crossover pump installed under the master bathroom sink (farthest fixture).
Result: Hot water at the master bath in 8 seconds instead of 35 seconds. Timer runs 6–8 AM and 6–9 PM. Cold water in the master bath is slightly warm (80F instead of 65F) for 15 seconds after the pump cycles. Monthly energy increase: $6. Total cost: $320.
Example 3: Demand Pump in a Condo
Setup: 800 sq ft condo with EcoSmart ECO 27. Chilipepper CP6000 demand pump installed under the bathroom sink with a push button on the vanity.
Result: Press the button, wait 6 seconds, open the faucet to instant hot water. Zero energy waste (pump only runs for the 6-second push). No warm cold-water issue (water only moves when triggered). Total cost: $280.
Key Takeaways
- A recirc pump delivers hot water in 2–10 seconds instead of 15–45 seconds
- Saves 3,000–8,000 gallons of water per year by eliminating the wait
- Demand pumps ($2–$5/year energy) are the most efficient option — use timer or demand, not continuous
- Crossover systems are the easiest retrofit — no new piping, $200–$400 total installed
- Navien's built-in ComfortFlow is the best integrated solution for tankless owners
- Budget $200–$500 for pump equipment, plus $100–$400 for installation (crossover retrofit)
- Continuous circulation with tankless adds $100–$300/year in energy — use timer or demand mode instead
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