The map in this illustration gives a general idea of the incoming water temperatures throughout the United States.  It is important to research out your area and get the coldest known water temperature expected in the winter for computing your hot water needs.

Three choices you must make in selecting a tankless hot water heater for your home or business:

• Incoming Water Temperature
• Maximum Flow Rate Required
• Electrical Service

Use the Heat Rise/Flow Rate Chart to help get a general idea of the size unit required.  Use the coldest water temperature known for your area in the Winter.  Also, consider using a desired flow rate of around 3 gallons per minute (GPM).  A more powerful unit will offer more heat thus more flow rate for your home. 

We recommend a sub-panel that can be purchased and shipped to you. This panel contains required circuit breakers as well.

Model Selector

How Big of a American Heat AH Model Tankless do You Need?  If you know how many gallons per minute you need with the chart supplied for the various items in your home then use the following simple formula:

* Heat Rise X 147 X GPM / 1000 = Tankless Heater Sized in Kilowatts

Heat Rise = Temperature of your incoming water minus the temperature of hot water needed

147 = watts of power to raise one gallon of water one degree Farenheit

GPM = Gallons per Minute

Divide the Products of these numbers by 1000

Put your calculator to the test...For example, if you have 65 degree water and you want 105 degree water then the heat rise needed is 40 degrees.  Multiply 40 times 147 and then multiply by the number of gallons per minute you need.  Use, say, 3 GPM for a nice flow for a regular bathtub faucet.  Divide these numbers by 1000.  In this case, 40X147X3/1000=17.64   Now that number rounded up is 18 kilowatts.  In this case you could use a piggy-back or in-tandem, two ADK units.  One as a pre-warm such as the ADK-3 (6.4 kW) hooked up to a standard ADK-1 (11.8 kW) to supply the power needed.  Or, you could consider using the next series of heaters by choosing an AH18 unit.  Note that if you need 18 kilowatts of power and you buy only an 11.8 kilowatt unit then you may come up short on those cold Winter days.  Our AH Models we offer are from 16 kilowatts to 27 kilowatts in power.  They are all 208/220/240 Volts.  If you want to compare other tankless water heaters then look for one that is rated 240 Volts and the kilowatt size you need.  This formula is simply using the laws of physics of heating hot water on an instantaneous basis.  The kilowatt size of an electronic tankless water heater is what you look for when comparing units.  All tankless water heaters are the same in the end...they heat water.  You need to know what size unit you need everytime though or suffer in the winter with less hot water!  And, if you like the convenience of pushbutton control of your hotwater and a limited lifetime warranty then consider our American Heat AH Models.

Ready to Order an AH Series Unit? 

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