There are three major factors playing a role in your home when choosing a tankless water heater.
1. Incoming water temperature
2. Desired flow rate
3. Electrical capacity in the home
The first thing you may want to start thinking about is if you use faucets like, Jacuzzi, over sized shower heads, massage, or body jets, in the home, as this will increase your demand for hot water and increase your model selection. Follow the steps below to size your unit correctly.
1. Incoming Water Temperature
In order to know your incoming water temperature please take a look at the map provided below, you will find a color coded map. Choose your color and look at the graph to choose your incoming water temperature.
2. Desired Flow Rate
Pick the faucets you will be using at the same time. The chart below will give you standard flow rate guidelines in (GPM) Gallons Per Minute for each faucet found in the home. Please keep in mind that these guidelines are based on standard fixtures and does not include Jacuzzi, larger shower heads, and or body jets, as these fixtures will increase your Flow Rate (GPM) Gallons Per Minute greatly. It is extremely important to understand how you will be demanding the ot water prior to picking out the applications as sometimes we feel we need to choose all fo the faucets found in the home versus what you will actually be using at 1 given time.
example: just because you have a 2-bathroom home, with a laundry, dish washer, tub, clothes washer etc.. does not mean you will pick all of them to calculate your application usage. Think of this a 2-bathroom home has a 40-gallon tank water heater you would not be able to run all of those applications due to the fact you only have 40 gallons of hot water stored, and by using all of the applications at one time would mean you would run out of hot water within minutes of turning on all of the faucets. Typically a 2-bathroom home you would calculate as at least a 2.5-3.5 Gallons per minute as at this rate with your tank water heater you would run out in 10 minutes.
3. Electrical Capacity
Check with your certified electrician for the electrical capacity available in your main electrical panel. In order for tankless water heaters to heat water instantly you will need to draw more power, but for a lesser period of time than your tank water heater, this is why you may be required to upgrade your breaker and wire size to adequately use your new tankless water heater. You want to check your voltage as well, as this may decrease or increase the kilowatt rating. If your amperage space does not hold the required breaker size you may have to upgrade your electrical to install the product.
Choose Your Tankless Water Heater
Now that you have you know your 3-primary factors, lets use them to size your applications. This is quite simple choose the column in which your inlet water temperature is placed. Second then scroll down until you find the correct flow rate you have calculated above, third scroll to the left and click on the model number.
Most people shower at a temperature of between 98°F and 104°F. The chart is based on a 240 volt input voltage and maximum flow rates are listed for various incoming water temperature levels. If your home or business has less than 240 volt power (208v), your maximum flow rate will be lower. Simply look up your incoming water temperature and desired flow rate to determine your model choice.