Tankless water heaters have become very popular lately for several good reasons. Tankless hot water heaters are more energy efficient than traditional units because they heat water as it is used, rather than heating and reheating water in a storage tank. They also take up significantly less physical space, as they do not have a bulky storage tank. But what kind is going to be right for your home and what should you know about them?
There are three types of tankless hot water heaters available:
Non-condensing: This is the first generation of tankless unit. These units use a heat exchanger to heat your water on-demand, and reach an Efficiency Factor (EF) of .82-.85. This technology has been in use in Europe and Japan for decades and is well-proven. The advantage of this type of unit is in reliability in that they are established products with few manufacturing issues. Some of the drawbacks of non-condensing units include hot exhaust, which means you have to install (expensive) stainless steel venting, and lower energy efficiency – in particular, the efficiency of these units drop when you use lots of hot water in short draws (i.e. washing your hands).
Condensing: Condensing units are the second generation of tankless water heaters. After a primary heat exchanger, these units use a second heat exchanger, which reuses the heat from your exhaust to further heat the water. This results in an increased efficiency of 92-94%. The benefit of cooler exhaust is that these units can be vented using (inexpensive) PVC, while the drawbacks included a higher unit cost and, similar to non-condensing units, a lower efficiency for short water draws.
Condensing hybrid: Condensing hybrid units are the third generation of tankless water heaters and were pioneered in the United States. These heaters incorporate a small – between 1 liter and 2-gallon – holding tank. This small holding tank keeps a reservoir of hot water, eliminating lower efficiency for short draws, meaning these water heaters achieve a true EF of .92-.96. A recent study by the Gas Technology Institute measured real life efficiency of condensing hybrid tankless water heaters and found the units consistently operated at 94% efficiency with little to no degradation due to short draws.
These units can also be vented in PVC which is less expensive. In some cases, the units also addressed “cold water sandwich” issues and pressure fluctuations that sometimes occurred with first and second generation models. There may also be slightly less lag in the time it takes to deliver hot water to the tap or appliance. One of the drawbacks (as of writing) of this technology is that because it’s newer, most models are manufactured by smaller companies. In some cases, there have been manufacturing-quality and warranty issues with these units. Product reliability is improving but it’s important to be careful about the brand you purchase.