In a typical home, 80 to 90 per cent of the energy used to heat water is lost down the drain. Drain water heat recovery (DWHR) systems help to recycle that hot water by collecting it and reusing it. They work by using wastewater to preheat water just before it enters the heater, doubling its output and cutting your costs in half.

However, DWHR systems are not one-size-fits-all. The size and configuration — and the money you’ll save on water-heating bills — depends on your home. There are a few things you should consider before installing one in your house.

Know your home

Look at your plumbing’s configuration. Is the water heater several metres from the plumbing stack that captures shower drainage? You’ll need extra pipe to carry pre-warmed water to your water heater, which means higher installation costs.

Do your homework

Choose the most efficient unit for the space you have. The longer the unit, the more surface area to capture heat — six or seven feet is the ideal length. It’s also critical to ensure that the DWHR system’s flow rating matches your home’s flow rating. Measure the service line coming into your house at your water meter: if it’s three-quarters of an inch, the flow rating is seven gallons (26 litres) per minute. If it’s half an inch, the flow rating is five gallons (19 litres) per minute.

Hire a professional

DWHR system specialty stores offer one-stop shopping for units and installation. If you don’t have one near you, find a plumber or contractor with experience in DWHR.