The two biggest reasons people become dissatisfied with their tankless water heaters are improper sizing and poor quality selection. A lot of units simply can’t keep up with the hot water demands of the average American household and end up wasting more money than they save. Ultimately, though, it’s up to you to choose the right tankless water heater to meet your specific needs. Consider the following tips:
Peak demand
Sizing a tankless water heater is different than sizing a tank-type water heater. Sizing a traditional water heater means estimating the volume of hot water you’ll need within a one- to two-hour timeframe. Sizing a tankless water heater means estimating peak demand in terms of momentary usage—in other words, what’s the most you’ll be running at the same time? For a single person with low demand, this could be a single shower. For others, this could be multiple showers plus the dishwasher. Go online and find a hot water calculator to get a good idea of your flow rate.
Flow rate
The primary measure you’ll hear people talking about with tankless water heaters is flow rate, which is measured in gallons per minute (GPM). In other words, how many GPM can be output while raising the water temperature by 35 degrees, 45 degrees, 60 degrees and so on? The larger the temperature rise, the less the unit can output. Look for a tankless water heater that’s marked with an “actual” flow rate.
Gas or electric
Electric tankless water heaters can be tricky to work with because they have lower outputs and require a lot of electricity. Each unit has its own electrical requirements, so you should consult an electrician prior to making a purchase. In terms of flow rate, most electric heaters can only run one major application (shower, dishwasher, washing machine) at a time.
When sized with the proper gas lines, gas tankless water heaters can supply more hot water and are better choices for those with medium to high hot water demands. Gas heaters can be installed both indoors and outdoors, although indoors is best for cold climates. Outdoor installations can be less expensive since you eliminate the need for vent piping.
High flow applications
If you find your peak demand is greater than any single unit can accommodate, consider a multi-unit (manifold) configuration. This type of setup is generally only required for commercial buildings such as condos, duplexes and restaurants, but it’s also occasionally used in residential buildings. However, if you think you might need a second unit, it’s likely your current unit is installed or sized improperly.
