How Many Batteries to Run a 1500 Watt Heater?

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Nothing warms you up during chilly days and nights like an electric heater, but it takes a toll on your power bill. So you decide to switch to a solar power system and run the heater off a battery bank. But how many batteries do you have to use?

A 1500 watt heater needs a 150ah 24V battery to run for an hour. To power a heater for 24 hours it would require 16 x 200ah 24V lead acid batteries. For a lithium battery bank, 8 to 10 x 200ah will be enough.

Calculate How Many Batteries a 1500W Heater Needs

Let us start with the basics. 1 kilowatt is equal to 1000 watts, so 1500 watts is 1.5 kwh. Most electric heaters run on 120 volts and draw 12.5 amps, but if you are going to draw power from a 24V battery, the amps per hour goes up.

The formula is:
1500 watts x runtime = total watts required
Total watts / volts = battery amps

If you want to run a 1500 watt heater for 12 hours, that would be:

1500 watts x 12 = 18000 watts

18000 watts is equivalent to 8 x 200ah 24V lead acid batteries with a 50% discharge rate.

A 24V 200ah battery is 4800 watts:

24 x 200 = 4800

With 8 of these that would be 38400 watts, but because FLA batteries have a 50% DOD, only half is usable. 38400 watts divided by two is 19200 watts, which is more than enough to run a heater for 12 hours.

If you want to run a heater for 24 hours you can repeat the steps above but replace 12 hours with 24. The result will be 16 x 200ah batteries as we mentioned.

Not only do you need a large battery bank, but the inverter must also be large enough for the heater and other appliances you want to run. This battery bank size is also for the heater only, you cannot use any other appliances alongside it.

Why 24V Batteries Instead of 12V?

Large appliances like refrigerators, AC units, washing machines and heaters work best with 24V and higher voltage battery banks. The higher the battery voltage the more watts it can handle.

A 100ah 24V battery has double the watts of a 12V battery:

100 x 12 = 1200
100 x 24 = 2400

A heater needs a lot of watts and amps to run, so it is more practical to use a 24V battery as you need less of it. If it takes 16 200ah 24V batteries to power a heater for 24 hours, you would need 32 of those if they were 12 volts.

Batteries are heavy and bulky. Lead acid batteries also require upkeep so the less you have to deal with the better. A smaller battery bank also means fewer solar wires and cables to work with. This is important if you live in a small house and don’t want to deal with multiple batteries.

Next you have to decide how to wire them together. Connecting the batteries in parallel boosts the amps but does not change the voltage. With a series connection you increase the volts instead of the amps. Either one will work fine, but your decision may be influenced by what other appliances you are running on the solar system.

Should You Use Lithium Instead of FLA?

Whereas FLA batteries have a discharge rate of 50, lithium batteries are good for at least 70% or even a 100%. You can get maximum use of the capacity – or almost maximum -, so it is worth considering.

The biggest drawback is the cost. While lithium battery prices have dropped, it is still quite higher than lead acid. And if you want to reduce the number of batteries, you can opt for a 24V FLA set than 12V.

If money is not an issue by all means go with lithium. There is no maintenance required and life cycles are better. But for most users, FLA battery banks will get the job done.

Deciding what batteries to use is crucial so you have to decide early. You have to weigh the pros and cons of FLA, gel, AGM and lithium. You also have to decide whether to get a 24V set or 48V. The higher the voltage the pricier, but you get more power out of them.

How Many Solar Panels and Batteries to Run a Heater?

But what happens if you combine solar panels with a battery bank? As we have explained in another post , it is possible to use a heater with PV modules. There are a lot of factors to consider, but overall expect better results.

A 1500 watt solar panel needs at least 5 x 300W solar panels to run. Assuming each PV modules can produce 300 watts an hour, five of these is good for 1500 watts. But there are a lot of factors that affect solar panel production that makes it difficult for a solar panel to generate 300 watts an hour.

Everything from clouds, the angle of the sun, rain etc. means you will probably get around 250-280 watts or even lower. This is all the more likely since you will be using the heater in winter. In that case you need at least 6 300 watt solar panels.

Benefits of Using Solar Panels and Batteries For a Heater

However this is assuming you will only use solar panels to run a 1500 watt heater. If you combine this with a battery bank however, you will be able to run the heater for longer periods.

If you have a 1500 watt solar array you only need 8 200ah 24V batteries to run a heater all day. You can run the heater on solar power for the day then when night comes, you can switch over to the battery. By the next day the battery bank will need recharging, but you can still use the solar panel.

So you do not have to choose between a solar array or a battery bank. You can use both. If you have a solar generator you can use that as an alternative to the battery. You can connect a solar panel to a solar generator to keep it going.

With solar panels and batteries, the important thing to remember is the more you have, the better. With a large system you can offset any drops in output due to the weather. Heaters are used in the cold, where solar production takes a hit.

A fully charged battery serves as a consistent power source for a 1500 watt heater. But if the solar array is not getting enough sunlight it will take longer to charge. But if you have a large solar system, it will have an easier time filling up the batteries.

Tips to Reduce Heater Power Consumption

If your heater is consuming too much power than it should, or you just want to save more on costs, here are some suggestions.

Take Advantage of the Sun. Open your curtains and blinds during the day. If the sun is out, take advantage of it to warm your house. This can help reduce your heater usage. When night comes, close all the blinds and curtains to keep the heat in as much as possible.

Insulation. Make sure your home is properly insulated for the winter. Even a powerful 1500 watt heater cannot help much if your house does not have insulation . Ask for professional help if you are not sure how to optimize its setup.

DIY House Fixes. Check for leaks, cracks, gaps etc. along the doors, windows and anything else cold air might get through. Before winter comes, do a thorough checkup of your home. All those small cracks may seem insignificant, but they play a huge role in those cold drafts you get exposed to.

Do Not Use the Heater All Day. This is a simple solution and probably the most practical. If it is not really that cold, you should turn the heater off, or at least use the lowest setting possible. You can do this around noon or whenever the sun is out.

Use a Smaller Heater. A 1500 watt heater is very effective during the cold season. But if you find yourself not using all of that power, maybe it is better to try something smaller. A 1000 watt heater may be acceptable and it will consume less solar energy.

Quality Design. Not all 1500 watt heaters are the same. Some are more energy efficient than others so look for the best one possible. Buying from a reputable manufacturer is essential so you should research the heater thoroughly.


Running a heater on solar batteries is similar to that of a fridge or AC, in that you need a lot of power. It is manageable but there is no going around the fact you need a good sized battery bank. By combining them with solar panels and good old DIY home fixes, heaters can be more efficient.