Will a 1500 Watt Inverter Run a 1500 Watt Heater?

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The answer to the question “will a 1500W inverter run a 1500W heater” is yes it can, but you probably should not. In this guide we will explain why and why a larger inverter is a better option.

A 2000 watt inverter can run a 1500 watt heater. If the inverter is powered by a 250ah 24V battery, the heater is going to last for 4 hours.

What Inverter Size Do I Need to Run a 1500 Watt Heater?

First to answer the question, why you should not use a 1500 watt inverter. The answer is simple, inverters should always have some reserve power.

A 2000 watt inverter is the best option for a 1500 watt heater because there is reserve power in case of a voltage spike. The system is equipped to handle a sudden influx of current and won’t damage the heater.

A 1500 watt heater needs 1500 watts to run and 2500 to 3000 watts to start up. That is similar to running an air conditioner on an inverter. Most 1500 watt inverters have a 3000 watt capacity so it is not a problem.

The problem is you will be running the inverter at maximum capacity. Ask any electrician and they will tell you to never load a power outlet to the limit. The same rule applies to an inverter.

A 1500 watt inverter running a full load has no protection in case of a power surge. A single voltage spike will damage the inverter and heater permanently. This will not occur with a 2000 watt inverter.

A 2000 watt inverter – we recommend the Novopal 2000 – also lets you run other appliances. You could turn the heater on and run a laptop. Or you could listen to a portable radio and turn on some lights.

The greater the inverter capacity, the more appliances you can run alongside the heater. Even if you just allocate the inverter for the heater, you have peace of mind knowing the system can cope with any spikes.

How Many Watts Does it Take to Run a 1500 Watt Heater?

A 1500 watt heater uses 1500 watts an hour. But if you run it on an inverter, the power consumption will be higher.

The reason for this is inverter efficiency, or the lack of it. Inverters use power even if there is no load, but efficiency is different.

An inverter consumes more power than the heater it is running due to inefficiency. The lower the efficiency rating, the more extra watts are needed to run a load.

Quality inverters have an efficiency rating of 90% and higher. There is no 100% efficient inverter.

So if you have a 1500 watt heater running on an inverter, you have to account for efficiency.

Assuming the inverter is 93% efficient, that means additional watts to the power used by the heater.

1500 / .93 = 1612

The heater uses 1612 watts. And right here you see the problem with using a 1500 watt inverter. It goes over the maximum capacity and could damage the system.

A higher capacity inverter should fix this. Of course you also need to make sure the inverter power source is sufficient.

Inverter efficiency ratings are improving rapidly. A few years ago 85% was considered the average efficiency rate. Nowadays that is poor and 93% to 95% is the ideal.

No matter what inverter size you buy for your heater, keep the efficiency rating in mind. It makes a huge difference in terms of power consumption and how much you save.

How Long Will My Inverter Run a 1500 Watt Heater?

To find out we need to know the following. How many watts the heater is, how many cycles it runs per hour, how long the heater runs and the battery depth of discharge rate.

To run a heater for 8 hours, you need a 2000 watt inverter and two 250ah 24V batteries.

First we assume you have a 2000 watt or larger inverter with a 93% efficiency rating.

You want to run a 1500 watt heater for 8 hours. Heaters usually run 2 to 3 cycles at hour, with each one lasting 10 to 15 minutes.

The heater won’t use 1500 watts an hour. Three 15 minute cycles per hour is 1125 watts, but let us round it off to 1500 watts for simplicity.

1500 watts x 8 hours = 12000 watts

You need a 12000 watt battery. 24V batteries are better suited for heaters than 12V so use those.

12000 / 24 = 500

You need a 500ah battery bank to run a 1500 watt inverter for 8 hours. A couple of 24V 250ah batteries is going to be enough. Or you can buy some 300ah Ampere Time lithium batteries to get extra power.

After 8 hours the battery bank will be completely discharged. If you use lithium batteries, a full discharge is no problem, but you should not do that with AGM or gel batteries.

Lead acid batteries have a 50% depth of discharge. Once the energy level drops to 50%, recharge it. You can keep using the battery but over the long term it will shorten the life cycles.

And you probably won’t even reach 0%. The battery will cease charging once it drops to a certain level (15%, 10% etc.).

If you are using lead acid batteries, double its capacity from 500ah to 1000ah. Either that or reduce the heater runtime in half.

Can You Really Run a 120V Heater on 12V/24V Batteries?

A 120V heater can run on a 12V or 24V battery with the aid of an inverter. The inverter converts DC into AC and allows any 120V appliance to run on a deep cycle battery.

Once conversion is done, the heater draws power from the battery as if it was a regular AC power outlet. The difference is the amps being pulled.

  • 1500 watts / 120V = 12.5 amps
  • 1500 watts / 12V = 125 amps
  • 1500 watts / 24V = 62.5 amps

A 1500 watt heater draws more amps if it runs from a battery. Some batteries can only handle 20 amps an hour, so make sure the battery bank is capable of handling this kind of draw.

You probably don’t have to worry whether your inverter supports 24V. In fact the largest systems only run on 24V and not 12V. Fortunately you can connect two 12V batteries in a series and get a 24V battery bank.

This is another reason why you should use 24V batteries with the inverter. 12V batteries are too small and simply won’t last. As long as your inverter and battery bank have the right specifications, there is no reason why a heater cannot run.

How to Reduce Heater Power Consumption

Even if you have a good sized inverter battery system, you should still look for ways to reduce the power consumption. And there are many ways to do this.

  • Buy an energy efficient heater. 1500 watt sizes are the most commonly used. But there are 500W and 750W models available. Calculate how much power you need. If 1500 watts is not necessary, use a smaller heater.
  • Buy an energy efficient inverter. The higher the inverter efficiency rating the better. 90% should be the minimum to look for.
  • Try the lowest settings . Heaters have different options so the lowest if it is sufficient. The temperature levels will vary every day so adjust the heater accordingly.
  • Timer. The timer is a handy device that turns the heater on or off automatically. Forgetting to turn off the heater will cost you dollars so make sure the timer is activated.
  • Use the thermostat. Set the thermostat to a level that keeps your place warm but without using too much power.
  • Insulate your home. This is a simple but effective solution. Seal all those cracks and crevices to keep heat from escaping.
  • Wear something warm. Another basic step but very effective. If you wear suitable clothing for the season, you won’t need to turn the heater on to high.


To sum it up, a 1500 watt inverter should never have a full 1500 watt load. This is applicable to all inverters regardless of size. The risk of a sudden power surge is real and could damage the system and the heater, so better get a 2000 watt or larger inverter.