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How to Add a Heat Pump to a Water Heater

This Old House plumbing and heating expert Richard Trethewey makes heating water more efficient by installing a heat pump

In this video, This Old House plumbing and heating expert Richard Trethewey makes heating water more efficient by installing a heat pump. Read on to see the steps for this water heater heat pump retrofit.

Steps for adding a heat pump to a water heater

  1. Shut off the cold-water line and electrical circuit to the water heater.
  2. Pump all the water out of the water heater's tank.
  3. Open a hot-water faucet in the kitchen to release pressure and break the vacuum in the tank.
  4. Use a pipe wrench to remove the drain valve from the water heater.
  5. Replace the old drain valve with a single-entry valve. Wrap plumber's tape around the female threads and tighten the new valve into the drain-valve hole.
  6. Attach two lengths of PEX flexible tubing to connect the heat pump to the single-entry valve on the water heater.
  7. Slip foam-rubber pipe insulation over each length of PEX tubing.
  8. Drill a ½-inch-diameter hole through the thermostat cover on the water heater, then attach a rubber strain-release fitting.
  9. Feed an electrical cable from the heat pump through the strain-release fitting and attach it to the thermostat on the water heater.
  10. Screw the thermostat cover back onto the water heater.
  11. Install a condensate pump to collect and discharge condensation from the heat pump to the washing machine drainpipe.
  12. Turn on the cold-water line and the electrical circuit.
  13. Fill the water heater's tank with water.
  14. Turn on the heat pump.