How Big A Generator Should Be To Power A Tankless Rv Water Heater ?

In our house, a water heater is a typical appliance. In chilly climates and during the winter, a water heater is necessary. We use electricity to power the water heaters in our homes, and generators can power a water heater. You must understand the prerequisites for operating a water heater. 

What size generator can run a tankless water heater?If the generator’s power output is sufficient to meet the water heater’s needs, it can power a water heater. For instance, a 4000–4500 watt electric water heater. Therefore, you will require a generator with a capacity of 5000 watts.

The question, “What size generator do I need?” will be covered in this article. The top tankless water heater options will be highlighted, and we’ll explain what size generator to run the water heater is ideal for you. 

What is a Tankless Water Heater?

A water heater without a tank is known as a tankless water heater. Tankless water heaters heat water using the thermosiphon concept, which circulates hot water around a metal coil inside the appliance.

If you own an RV and enjoy going camping, you are aware of the need to install a tankless water heater. It is portable, doesn’t require routine water tank refilling, and is environmentally friendly to use a tankless water heater in your RV.

How Does a Tankless Water Heater Operate?

Tankless water heaters operate differently from conventional water heaters. Instead of requiring a tank, a tankless water heater uses a small pump to circulate warm water around a heating element. This indicates that you don’t need to fill your tank up constantly. RVs greatly benefit from tankless water heaters because of their small size and simplicity of installation.

Use a Variety of Generators to Run a Water Heater

Generators come in a variety of sizes and power. You must be aware of which size generator is appropriate for running which water heater. “How big of a generator do I need to power a water heater’ is always a prime query.

You can utilize a generator with extra power, each with its specifications, to control your water heaters. You can determine the size of the generator for the water heater by looking at the different types of generators listed below.

2000 watts

 For high-power appliances like water heaters, 2000 watts is a relatively insignificant amount of power. Therefore, not all types of water heaters can be powered by a 2000-watt generator.

Since a gas heater requires less wattage, you may only use one type of water heater with this generator.

4000 watts

A generator with a power output of 4000 watts is also insufficient to power a water heater. Therefore, since the majority of water heater models demand more power than 5000 watts, a 4000-watt generator might be able to power a gas water heater.

5000 watts

With a 5000-watt generator, you can power numerous water heaters. However, you must make sure that the power requirements of the generator and water heater are compatible.

A water heater powered by electricity typically requires 4000–4500 watts to start. Therefore, you must guarantee wattage above this range.

5500 watts

Running water heaters at 5500 watts is generally acceptable. Since most water heaters need more power than 5000 watts, a 5500-watt generator can readily power a medium-sized water heater.

6500 watts

A water heater can be operated at 6500 watts as well. With a generator of this capacity, you can run several devices in addition to the water heater.

7000 watts

7000-watt generators can power water heaters. Additionally, you can use this generator to power most water heater, models. However, this generator will not work with a tankless water heater.

7500 watts

A 7500-watt generator can power many different kinds of water heaters. But a significant amount of electricity is needed for tankless models. Therefore, a 7500-watt generator cannot power a tankless water heater.

10000 watts

A generator with a 1000-watt capacity is quite large. With this generator, you can run various appliances in addition to an electric or gas water heater.

12000 watts

These generators, which range in power from 12,000 to 14,000 watts, can frequently keep a home running continuously. Everything plugs into a socket, including lights, heaters, televisions, freezers, laptops, and water heaters, will function. This is the right kind of generator for a house. 

The Amount Of Generator Required To Run Common Water Heaters

Numerous factors, including the number of additional devices you intend to operate alongside it, affect the amount of electricity needed to keep a water heater operating. The most important factor, however, is the present water heater. Knowing what size generator to run a water heater is made easier by these factors. 

Only 1,200 watts are needed to run a basic gas-powered generator. A gas heater suggests that you might be able to run it off of a reasonably small power generator. Remember that if you get a cheap generator, then you may just be able to run the water heater.

To operate properly, electrical water heaters normally need at least 4,000 watts. You will still require at least 4,200 watts even if you utilize a smart water heater. When picking a generator, it’s important to consider how many watts it can generate. Many people question whether we can run a water heater off a portable generator. 

The answer is typically no because most generators do not have 4,500 watts. For large voltage applications, such as running specialized equipment or connecting to the home during an outage, a 240V option is essential. A 120v generator would be plenty if you only needed 3500 watts or even less. The best alternative is a generator with 120 or 240v outputs.

Let’s examine the wattage requirements of a water heater now.

Water heater powered by gas

The power needed by gas water heaters is not very high. A typical gas water heater typically requires 1500 watts to operate; consequently, a 2000-watt generator can power a gas water heater.

Heater for electric water

Unlike a gas-powered water heater, an electric water heater will require more watts. An electric water heater uses between 4000 and 4500 watts and requires 3500 watts.

A water heater in a tank

A tank water heater will also require between 4,000 and 5,000 watts. As a result, the tank water heater uses more energy than a gas water heater.

Tankless water heater

An enormous quantity of watts is required to operate a tankless instant water heater. A tankless water heater typically uses between 10,000 and 30,000 watts to operate.

How big of a generator do I need for the water heater?

Generally speaking, the sort of water heater you use will determine the size of the generator. In addition, the configuration of the house affects the generator’s size.

Various kinds of water heaters will require different amounts of power. Let’s examine the size of the generator required for the water heater.

Heater for electric water

A medium-sized generator is required for an electrical water heater. The optimal generator for the electric water heater will be between 5000 and 6000 watts.

A water heater fueled by gas

A 2000-watt generator is required if the water heater is gas-powered because a gas water heater has a 1500-watt operating capacity.

A tank water heater and a tankless water heater

Tank and tankless water heaters require various sizes of generators, and a 5000-watt generator can often power a tank water heater. On the other hand, a tankless water heater requires at least a 10,000-watt generator to operate.

How Should A Generator Be Connected to A Hot Water Heater System?

Start by attaching the hot water system to the most suitable generator size. Get one 10/3 AWG 25A cable to run from the water heater to the generator first. Attach the 10/3 cable to the A15-20 socket to create a custom power cord. 

They attach one end of the special electrical wire to the connection link at the top of the water heater. One end should be connected to the generator’s 240-volt outlet. To lock the cord, use the twisting lock mechanism.

Cost To Run A Generator To Power A Water Heater

The type of generator you use and how long you use the water heater will determine how much it costs to run a water heater on your generator. In contrast, a tankless water heater will cost more to operate than a gas-powered water heater.

It’s not quite as cheap as all those straightforward generators made for power tool use. It will cost you close to $400 for a portable generator that can produce a maximum of 50,000 watts, or perhaps more. The price could go up to $3,000 or even more if you need a large generator with a power output of 12,000 watts or more. A generator to power a house requires a high cost. 

An electric water heater would typically cost between $750 and $800 per year to run on your generator for three hours per day, and it can therefore cost as much as $66 per month. It will be less expensive if you utilize a gas-powered water heater.


What is the amp needed for an electric tankless water heater?

Tankless heaters can consume between 42 amps and 167 amps of power. Because we are aware of two crucial parameters, we can determine exactly how many amps a tankless water heater uses: total energy or watts. Power input for electric tankless water heaters ranges from 10,000W (10 kW) to 40,000W (40 kW).

Is It Possible To Install A Tankless Water Heater In My House?

A new tankless water heating system can be installed where the old system was. A large water heater may not be able to be installed in the basement of a two-story house.

What is the energy consumption of a tankless water heater?

Electrical tankless heaters use up to 30,000 watts of power when they are “on.” For instance, the power consumption of a typical washing machine is somewhat higher than 1,000 watts. Electric tankless water heaters do not, however, run continuously.

Are tankless water heaters more energy-intensive?

For families that utilize 41 gallons or less of hot water per day, tankless heaters can be 24–34% more energy-efficient than traditional water heaters. For households that consume about 86 gallons per day, tankless heaters can be 8–14 per cent more energy-efficient.

Can an inverter generator power a hot water heater?

An inverter generator can indeed power a hot water heater. But the electricity needs must line up. You can use an inverter generator to power a gas or electric water heater.

Otherwise, due to its lower power input, an inverter generator won’t be able to power a water heater.

A portable generator can power a water heater?

Generally speaking, a portable generator can be connected to a water heater. However, you cannot run the water heater continuously due to the low power output of the portable generator.

Sometimes a portable generator cannot power a powerful water heater. You can use a portable generator to power a water heater that runs on gas.

How Much Power Is Required for a Generator to Power a House?

Which size generator to run a house seems to be an important matter. You may use a generator with a 5,000–7,500 watt rating to power even the most essential home appliances. All these devices can be operated simultaneously by a 7500-watt generator.

Final Thoughts

A generator can run a water heater; however, the generator’s wattage requirements must be met by the water heater. A 5000-watt generator can be used to power an electric or gas water heater. 

However, a 5000-watt generator will not be able to power a tankless water heater. The continuous output wattage of the generator must be greater than the constant wattage needed by the water heater to operate a water heater on a generator.

Your water heater can run on a generator that generates 5 kilowatts of power if it consumes 4 kilowatts. The generator is the best, especially if you want to power every other appliance in the house.

Tankless water heaters powered by gas and electricity operate more efficiently than traditional water heaters powered by the same fuel. We gave the annual cost of energy usage for a gas model an excellent rating, but only a fair rating for an electric one. Very efficient in terms of energy. Finally, it is understandable now what size generator to run a tankless water heater is needed. 

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