Tankless water heaters, whether gas or electric, are highly efficient compared to traditional water heaters. While a gas tankless unit uses propane, some parts of the water heating system still use electricity. So, what are the electrical requirements of a tankless gas water heater?
Most tankless gas water heaters require a 15 ampere or 20-ampere 120-volt circuit to power the electric pilot light and the control board. The National Electrical Code requires instantaneous water heaters to have circuits not exceeding 120 amperes and protected at not more than 150 amperes.
Tankless gas water heater electrical requirements can vary depending on whether you live in an area with 220 volts or 110 volts power supply. The circuit’s electrical requirements will be sized based on the wattage of every individual unit or brand. Voltage rating can be 208V, 120V, 240V, or 277V.
Electrical Requirements of a Tankless Gas Water Heater
According to the National Electrical Code, tankless gas water heaters should be supplied with a 15-20 ampere 120-volt electrical circuit that powers the unit’s control board and ignition device. The setting of the circuit breaker determines the circuit ratings since the control circuit is an individual load.
A propane tankless water heater has an electrical control circuit that ensures a proper supply of power to the control board. The control board detects the temperature of the water the tankless unit is being fed with and also that of the water that leaves the water heater into the faucets in the home.
Control boards require electricity in order to operate. When properly supplied with power according to the NEC code, the control board is able to control the amount of heat required to heat water to the desired temperature.
Once the desired temperature is determined, the control board initiates an electronic ignition sequence that will result in water being heated to the desired temperature and delivered to the point of demand in the home.
Whether you’re using a Rinnai, Takagi, EcoSmart, or Rheem tankless natural gas water heaters, the manufacturer will have determined and specified the circuit size. For example, Rinnai tankless water heaters come with an electrical requirement of 120 volts AC, 60 Hz, and less than three amps.
The units usually come with clear installation instructions to help you or your technician with the correct installation.
Electrical components in a tankless gas water heater
Most homeowners make the assumption that a gas water heater can run when there’s a power outage. While the tankless unit does not use electricity as fuel to heat the water, it may be dependent on some electric components in order to function properly.
Here are the electric components in your tankless gas water heater:
Electric control board
An electric control board is an important part of the tankless gas water heater. Electric control boards relay information and monitor communication between all electrical components in a series circuit. This is what allows for proper operation without interference or malfunctioning.
The electric control board is like the PC unit of the water heating system. It uses electricity to operate the water heater, which is why your gas instantaneous water heater may not work when there’s a power outage.
The electric control board senses the temperature of the water flowing into the tankless unit and instructs it to turn the burners on or off depending on the detected temperature. In short, this circuit board controls the gas valve, burner, and temperature of the water. This is how hot water is supplied on demand in your house.
Gas pilot light
A gas pilot light is an integral part of the gas safety mechanism in some models of any propane or gas hot water system. The pilot light is a small flame that is kept lit in your water heating system.
The gas pilot light is controlled by the electric control board. If there’s a need to heat water, the pilot light is signaled to ignite the burners to heat water to the required temperature determined by the control unit.
Keep in mind tankless gas water heaters heat water almost on demand, which means they are economical on energy consumption compared to tank-style water heaters that consume more power to maintain water temperature all day.
Electrical Requirements for Different Brands
The electrical requirements of tankless gas water heaters can vary depending on the model and brand. The heating capacity of these units varies a lot depending on the requirements of each household. That means that circuit breaker installations, electrical wire gauges, and resistance will vary a lot.
Some of the common brands here in the U.S are Takagi, Rinnai, Stiebel Eltron, Mitsubishi, and Eemax. It is important to check their installation manuals to make sure you get the electric requirements spot-on and prevent any hazards.
Here are the electric requirements for some of the units:
Rinnai tankless water heaters require 120 volts AC power at 60Hz frequency and less than 3 amperes. The tankless water heater needs to be connected to a 120-volt outlet and is powered by a 60Hz current which means it can only be used in the United States, Canada, Mexico, or parts of South America with backward compatibility as far back as 50 cycles.
The electrical requirements for Rinnai tankless water heaters are variable and range from a 20 amp circuit breaker to the need for multi-phase power.
The electrical requirements for Takagi tankless water heaters are 120 V AC 60 Hz and draw less than 2 Amps. The outlet needs to be on a dedicated circuit and should not exceed 70% capacity in terms of power consumption or else the breaker will trip.
A GFCI outlet is recommended but if that isn’t possible then an arc fault protection device (AFCD) that shuts off electric current when it detects arcing inside the home’s wiring is required by law.
Regardless of where you live, tankless gas water heaters should be installed by a licensed electrician to ensure the safety and legality of the installation. It’s also advisable to have an electrical inspection done on your home before installing tankless gas water heater electrical requirements in order to identify any issues that might arise with its use.
- National Electrical Code Style Manual
- Takagi: Instantaneous Water Heater Installation Manual and Owner’s Guide
- Thomas L. Harman, IAEI Magazine: Go Tankless…And Stay In Hot Water