Nobody likes to send money ‘down the drain’, but that is exactly what we are doing when we let our heated water drain from activities like showering or washing dishes. This is because drained hot water contains valuable energy in the form of heat that can be recovered for further use in the home. For the same reason we use home insulation, the less heat wasted, the more we can cut down on our home’s energy costs.

Luckily, systems are now available for your home to recover heat from drained hot water and put it to further use. These systems are known as drain water heat recovery units and are gaining popularity in renovations and home additions in Ottawa as a green technology option.

In fact, Ontario was the first province or state in North America to list drain water heat recovery units in building code as part of recognized energy saving building options.

Drain water heat recovery units are widely available for residential use and are designed to capture heat from drained water for use in preheating fresh cold water. This process helps to lower the energy (and money) required to heat new water using your water heater as heat from existing hot water is transferred to the fresh water we want to heat before the water heater is even involved.

Although the process may seem a bit complicated, the results are not: lower home energy bills each month due to the reusability of the heat from your drained hot water.

How does the system work?

The first question many people have when they first hear of drain water recovery units is: ‘why would I want to reuse dirty, drained water?’  Of course, these units don’t reuse the dirty water itself, but rather the heat from the drained water. This is accomplished by a series of copper coils that are wrapped around the copper drainpipe that forms the drain water recovery unit. These pipes are used instead of traditional drain lines.

Known as a double wall heat exchanger, this coiled drainpipe system allows heat to be exchanged from the outgoing drained hot water in the copper drainpipe and the incoming fresh water in the copper coils around the pipe – all without the two streams ever touching and mixing.

This means that the only part of the drained water that is transferred to the fresh water is the heat. It also means that the fresh water is pre-heated prior to entering the water heating system or appliance and this saves energy and money during the heating process.

Where can these systems be installed?

Drain water heat recovery units are typically installed as part of the drainage stack below showers and leading to the hot water tank where the heated water can be stored. Showers make the most effective use of the heat recovery system as they both expel hot water and use hot water at the same time in large quantities.

In fact, these heat recovery units will increase the hot water supply to showers and ensure that the age-old problem of running out of hot water is greatly reduced. That also means that the lifespan of your hot water heater is increased as it needs to work less to heat water thanks to the assistance of the drain water heat recovery system.

What about tankless water heaters?

Drain water heat recovery units also work with tankless water heaters, however they will only be effective with showers since without a storage tank, the heat must be used during the simultaneous flow of heated drain water from the shower and the feed of cold water to the tankless heater on demand for the shower.

This also means that dishwashers or clothes washers won’t benefit from drain recovery with tankless water heaters as the simultaneous flow is not significant enough to recover useful heat.