Drain Back Solar Water Heaters in Northern Climates

A drain back solar water heater is a type of water heater that removes the fluid from the solar collector when the collector is not operating. It does so by using a drain valve and draining the water automatically into a storage reservoir for later use. The main advantage of drain back solar water heaters is that the home owner can use potable water inside the solar collector. They don’t need to worry about damage caused by freezing, as the water is drained down and out of the system during the evening or when the solar system is too cold.

While drain back solar water heaters work well in warmer climates, they can be problematic in northern climates. Even though the water is removed from the system, there is still a chance that any residual water left in the system may freeze if the surrounding temperature drops low enough. If this happens, the damage to the heating system can be substantial. In very cold weather, there is always a high danger that water will freeze quickly and block the system.

Drain backs also use a solenoid drain valve, and as such are prone to mechanical failure. If the valve fails in the winter, say good bye to all your solar collectors and the piping found outside. For this reason, you may want to consider using a closed loop solar system that uses an antifreeze heating medium, instead of directly trying to heat the potable water in the collector. A closed loop system utilizes a heat exchanger, either externally or inside the tank to transfer the heat energy. Because it has antifreeze in the solar heating loop, these kinds of closed loop systems are ideal for solar heating in colder climates. A pump failure in a closed loop system will not result in failure of the piping and the solar collectors.

So if you are in the market for a solar water heater and live in Canada or the Northern USA, consider your options and choose wisely!