What's the simplest way to add hot water recirculation to reduce wait time and water waste?

Short answer

The simplest, most DIY-friendly way to add hot water recirculation is to install an under-sink crossover recirculation kit. These retrofit kits use a small pump (usually at the water heater) and a thermostatic valve under the farthest sink to send cooling hot water back through the cold line until hot water reaches the faucet—cutting wait times and water waste without running a new return pipe.

How it works and why it’s simple

• A compact pump mounts at your water heater’s hot outlet.
• A crossover valve installs between the hot and cold lines under the farthest sink (or the sink with the longest wait).
• When the water in the hot line cools, the valve opens and the pump moves that cooler water into the cold line until hot water reaches the valve. Then it closes.

Typical kits: Grundfos Comfort System, Watts Premier 500800, Taco Hot-Link. Expect $180–$350 for a complete kit.

Pros:
- No dedicated return pipe needed.
- Install in 1–2 hours with basic tools.
- Reduces both wait time and water waste.

Cons:
- The cold line at that sink may be slightly warm right after a recirculation cycle.
- Uses a small amount of electricity and adds standby heat loss unless controlled by a timer/smart plug or built-in thermostat.

Step-by-step: Installing a crossover recirculation kit

Time: 1–2 hours for most DIYers.
Skill: Moderate DIY.

What you’ll need

• Recirculation kit (pump, crossover valve, and braided flex supply lines)
• Adjustable wrench and/or channel-lock pliers
• Teflon tape (PTFE) or pipe thread sealant (for threaded connections at heater)
• Bucket and towels
• Screwdriver (for hose clamps/valve brackets if included)
• Pipe insulation (1/2–3/4 in. foam, rated for hot water)
• Smart plug or plug-in timer (if your kit doesn’t include scheduling)
• Non-contact voltage tester if adding/using an outlet

Before you start

• Verify you have a standard tank water heater and a nearby 120V outlet for the pump. Tankless systems often need a manufacturer-approved pump/control kit—see “Special cases” below.
• Identify the farthest fixture (often an upstairs bathroom sink). That’s the best place for the crossover valve.
• Check shutoff valves under the sink are functional. Replace sticky or leaking valves before proceeding.

Installation at the water heater

1. Turn off power/fuel to the water heater.
   • Electric: switch off the breaker.
   • Gas: set to Pilot or Off.
2. Close the cold-water supply to the heater. Open a nearby hot faucet to relieve pressure.
3. Disconnect the hot outlet flex connector from the water heater. Have a towel/bucket ready.
4. Mount the pump on the heater’s hot outlet per the manual.
   • Use Teflon tape on threaded connections.
   • Ensure the flow arrow points away from the heater.
   • Many kits include a built-in check valve—keep it oriented correctly to prevent reverse flow.
5. Reconnect the hot outlet flex line to the pump.
6. Restore the cold-water supply and check for leaks at the new connections (do not power the pump yet).

Installation under the far sink

1. Close the hot and cold angle-stop valves under the sink.
2. Place a bucket under the supply lines. Disconnect the existing braided lines from the faucet.
3. Install the crossover valve between the hot and cold supplies per the kit diagram.
   • Usually: the valve mounts between the two angle stops using the provided tees/adapters; then new braided lines go from the valve to the faucet’s hot/cold inlets.
   • Tighten snugly—don’t overtighten brass or plastic.
4. Open the angle-stop valves and check for leaks.

Power up and purge

1. Open a couple of hot faucets in the house to purge air for 1–2 minutes.
2. Plug in the pump. If your kit includes a timer or thermostat, set it per your usage pattern (e.g., mornings/evenings).
3. Restore power or gas to the water heater. Set water temp around 120°F for safety unless using a whole-home mixing/anti-scald valve.

Settings and optimization

• Use a timer or smart plug to run the pump only during peak use times. This reduces energy loss and keeps cold water from warming when you don’t need hot water.
• Insulate accessible hot pipes near the heater and any long runs to cut heat loss and shorten reheat cycles.

Tools/materials summary

• Pump kit (Grundfos/Watts/Taco) with crossover valve
• Adjustable wrench, channel-lock pliers
• Teflon tape or pipe dope, towels/bucket
• Plug-in timer/smart plug (optional, recommended)
• Pipe insulation sleeves

Safety and code considerations

• Use only potable-water-rated components and seals.
• Plug the pump into a grounded outlet; use GFCI protection if required by local code (common in garages/basements).
• Keep gas water heater clearances and combustion air unobstructed.
• Don’t raise heater temperature above 120°F unless you have an ASSE 1017 mixing valve at the heater to prevent scalding.

Tips for best results

• Choose the sink truly farthest from the heater for the crossover valve—it improves whole-house performance.
• If the cold tap runs slightly warm right after a cycle, add or tighten scheduling to reduce how often it runs.
• Insulate the first 10–15 feet of both hot and cold near the heater and any long accessible runs.
• If you have a recirculation return line already (common in some homes), use a dedicated-return pump with an aquastat and check valve instead of a crossover kit for better performance and less cold-line warming.

Common mistakes

• Installing the pump backward (watch the flow arrow).
• Forgetting the under-sink check/thermostatic valve—without it, you can get continuous crossflow and warm cold water.
• Running the pump 24/7. Use a timer/thermostat or demand control to cut energy use.
• Skipping leak checks after the system heats up; fittings can weep once hot.

Special cases and when to call a pro

• Tankless water heaters: Many need a specific recirc kit/controller to avoid short-cycling or error codes. Check your manufacturer’s approved solutions (e.g., internal recirc with buffer tank, external pump with demand control). Consider hiring a pro for tankless setups.
• Home-run PEX manifolds: You may need multiple crossover valves or a different strategy. A plumber can advise on the most effective branch to target.
• No outlet near the heater or under the sink: Have an electrician add a properly grounded (and GFCI-protected if required) receptacle.
• Dedicated return line available: Use a true recirculation pump with an aquastat on the return line; performance is better and the cold line remains cold.

Rough costs

• Retrofit crossover kit: $180–$350
• Dedicated-return pump (if you have a return line): $200–$450 plus parts
• Electrician to add an outlet: $150–$300 (varies)

Typical specs (example)

Pump power: 120V, ~0.2–0.5A
Connections: 3/4" NPT (heater), 3/8" or 1/2" under-sink flex lines
Thermostatic valve: opens ~95°F, closes ~105°F
Max head: ~6–10 ft (sized for circulation, not lifting)

By starting with a crossover recirculation kit, most homeowners can dramatically cut hot water wait times in a single afternoon, without opening walls or running new piping.