How to Descale Water-Source Heat Pumps

Erin Watson-Price

According to the Geo-Heat Center, hard-water scales form on both open loop, water-source heat pumps and closed loop heat pumps with desuperheaters that provide hot water to the home. When the water source is high in calcium and magnesium, the temperature of the heat exchanger can cause the minerals to precipitate out of the water and form scales on the inside of the tubing. These scales build up over time and can slowly reduce the efficiency of a heat pump. Descaling, or removing hard-water scales, requires circulating an acidic solution through the heat exchanger. The acid reacts with the mineral deposits, allowing them to dissolve into solution and be flushed away.

  1. Contact a service technician to test the heat exchanger and determine the composition of the scaling. The particular composition and thickness of the scale will determine the acid solution you will need to use.

  2. Disconnect the heat exchanger.

  3. Attach a recirculating pump to both openings on the heat exchanger.

  4. Inject acid solution into the heat exchanger and monitor mineral output and pH. As the hard-water scales begin to dissolve, the pH of the solution will reduce. If little mineral output is recorded, increase the strength of the acid solution.

  5. Stop circulating the acid solution once the pH remains stable as an acid and no more mineral deposits are present.

  6. Rinse the heat exchanger with a neutralizing solution to stop the effect of the acid and prevent metal corrosion.

  7. Reconnect the heat exchanger and fill with water containing a small amount of neutralizing solution. This will remove any remaining acid and prevent it from contaminating the heat pump system.