Information Guide

What Size Generator To Run Hot Water Heaters

If you’re wondering can a generator run a tankless water heater, it can, but you need to make sure that all your voltages & watts match.

by Josh Mitchell

water heater is an essential appliance in every home. You use hot water for cooking, cleaning, washing, and more. Without it, you run into many inconveniences. You may want to consider using a generator to run your water heaters.

But, you’ll need to first know what size generator to run a hot water heater. 

generator size

You can, as long as you make sure the voltage is safe for your water heater. For instance, you can connect a 120-volt generator to a 240-volt water heater safely. 

Although you won't be able to do the same with a 240-volt generator to a 120-volt heater- this will overload the machine. 

Most tank water heaters run for three hours daily. This keeps your stored water hot. Most use about 4,000 watts, so you need to know that the generator will supply them. 

Are you wondering, "can a generator run a tankless water heater”? It can, but you’ll still need to make sure that your tankless heater system isn’t going to be overloaded by the process.  


What Size Of Generator Is Needed To Run A Water Heater System?  

Your water heater either uses 120 or 240 volts. That means you need to make sure the generator doesn't go above those numbers. 

If it does, the heating and electrical elements of your hot water heater will quickly burn out... leading to repair requirements. 

You don’t want to exceed the number of watts the generator produces. 5,000 watts should be enough for some units, but you don’t want to go over that amount when using a 5,000 watt generator. 

To be safe, it’s always best to go up in size. That way, you’re always covered where you need to be.   

Your water heater either uses 120 or 240 volts. That means you need to make sure the generator doesn't go above those numbers. If it does, the heating and electrical elements of your hot water heater will quickly burn out... leading to repair requirements. 

You don’t want to exceed the number of watts the generator produces. 5,000 watts should be enough for some units, but you don’t want to go over that amount when using a 5,000 watt generator. To be safe, it’s always best to go up in size. That way, you’re always covered where you need to be.   

Water heaters do take a lot of power to run. Most use between 4500 and 5500 watts. Most of the time, you'll need to have a generator dedicated to your hot water heater so you don't exceed the watt limit. 

However, it’s not a practical process to run everything on a generator. This is especially true if you also have a well pump, you could well exceed 10,000 watts trying to run everything at a single time. 

With a 7,500 watt generator, you should be able to run your hot water without coming close to the limit. As long as you make sure to check the numbers on your hot water heater, you should have no issues! 

Overall, you want to make sure you’re getting the proper kind of generator for the task. If it’s way too high in watts, it’s going to overload your device with electricity. Then, you’d have to repair the tank before you could have hot water again. 

Will A Generator Run A Hot Water Heater

How To Connect A Hot Water Heater To A Generator  

Step One 

Remove the covers that protect the immersion heaters in the tank. Make sure that you check for the amount of watts the appliance uses, then make a note of them somewhere you can easily see it.  

Step Two 

Calculate the number of volts, watts, and amps the water tank uses to run. Many generators have outlets for differing amounts of volts- you want to use the one that's appropriately rated for your machine. 

Step Three 

Connect the circuit breakers and the generator to the hot water heater. You want to make sure that everything is powered off, unplugged, and cut from the breaker before attempting to do this. 

Step Four 

Connect the ground wires properly and make sure that no components or wiring are exposed. Then, make sure to put the covers back onto the machines. You want everything secure. 

Step Five 

Make sure the breakers are off, then start up your generator. You can turn the breakers on, then make sure the generator is running safely. It makes a lot of noise, but that’s normal. 

How To Connect Hot Water Heater To Generator

People also Ask (FAQs)

How many amps does a water heater need?  

Your average water heater needs about 18.8 amps, 240 volts, and 4500 watts. The average gas powered heater uses a lot less, about 12 amps and 115 volts. You'll want to consider this when choosing a generator. 

How much would it cost to run a generator for a water heater?

Running a generator for about 24 hours, a full day, is very expensive. You can expect to spend $200 on this type of job. 

How many volts does a hot water heater use?

Your typical hot water heater uses 240 volts. You’ll need to inspect your appliance and make sure that’s correct before getting a generator. 

Are water heaters 120v or 240v generally?  

Most use 240 volts, but you can find ones that use 120 volts. It's always a good idea to measure your appliances if you’re unsure. 


Conclusion

To summarize, you need to know what size generator to use. Otherwise, you could run into several issues while trying to use your hot water heater normally. Make sure it’s installed correctly first. 

Josh enjoys researching, testing and diving into home improvement & DIY products. He has a passion for tools, learning new skills and fixing the everyday problems that arise around the house.

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