Choosing the Best Tankless Water Heater for You
In order to determine the best tankless water heater for your home, you'll need to examine a few variables. First, determine the flow rate that the tankless water heater will need to accommodate.
The flow rate is the amount of water (measured in gallons per minute or gpm) you'll need heated at any given time. If you're looking for a tankless water heater for a single sink, you'll need one that accommodates only the flow rate of the sink. If you want one for an entire bathroom, or even your entire home, you'll need to add up the flow rates of all the faucets, showers, or appliance that may need hot water all at the same time.
It's unlikely that all your sinks will be in use at once and even more unlikely that they'll all be using hot water at the same time. You will need to consider, however, the possibility that your dishwasher may be running at the same time you wish to shower.
In 1992 the Federal Energy Policy Act declared that the maximum flow rate for any one household fixture could not exceed 2.2 gpm at 60 pounds per square inch (psi) and 2.5 gpm at 80 psi. In order to conserve water and save money, some people choose to use aerators on some fixtures, making them just as useful but without the waste. You'll need to know the flow rates of your fixtures, or at least a general idea of their flow rates, in order to choose an appropriate tankless water heater.
Some general rules:
- Bathroom faucets – Standard flow rates are usually 2.2 gpm but fixtures pre-dating 1992 may be slightly more. At low-flow settings, they usually have a flow rate of between 0.5 and 1.5 gpm.
- Kitchen faucets – Most kitchen faucets have a flow rate of 2.2 gpm but earlier models may have a gpm between 3 and 7.
- Showers – Most modern showers have a flow rate of 2.2 gpm when operating at full blast. Low-flow models have flow rates between 1 and 2 gpm while earlier models can have flow rates as high as 8 gpm.
Secondly, you'll want to look at the temperature rise required to heat your existing water to your desired hot water temperature. This means you'll need to know the temperature of the groundwater, or unheated water in your pipes, and how many degrees you'll need to heat it in order for it to be hot. Most groundwater temperatures stay the same throughout the year and are roughly equal to the average yearly air temperature.
Next, determine the desired temperature for your output of hot water. Calculate the difference between this and your groundwater and you'll have the required temperature rise for your tankless water heater. For example, if you know that the hottest water you'll want out of your faucet should be about 120 degrees and your groundwater is around 60 degrees, you'll need a tankless water heater that can accommodate a temperature rise of 60 degrees at your calculated flow rate.
Tankless water heaters come in a variety of sizes and options and you'll be able to choose one that best suits your needs if you know the flow demands on a single unit and the temperature rise required at that flow rate. Keep in mind you can install multiple tankless water heater units that can either act as a single function (for one output source) or multifunction (an entire bathroom or rooms).
Electric units are commonly used for single function or small rooms while gas-fueled tankless water heater systems are more commonly installed to provide hot water for an entire home. Electric units can, however, be installed beside one another to accommodate an entire house if gas is either unavailable or not desired.