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A space heater requires a lot of power, which is why they are often used on an AC load. However an inverter with sufficient power can run it. Under this configuration the heater runtime will be determined by the inverter capacity and other factors.
A 2000 watt inverter can power a 1500 watt heater, but its run time will depend on the battery capacity. A 300ah lead acid battery will last one hour if the heater draws 1500 watts continuously.
How Much Inverter Power Does a Heater Need?
Most single setting heaters use 1500 watts, but there are smaller units ranging from 1000W to 2000W. There are also multiple setting heaters which can be set to 750W and 1500W, 1000W and 1500W or 500W, 1000W and 1500W.
A 2000W heater is ideal for a 1500W inverter. A 1500W inverter is enough on paper, but due to inverter inefficiency you should opt for 2000 watts., Plus you will want more power in case of a voltage surge. A high quality system like the Ampeak 2000W Power Inverter will be just fine for heaters of this size.
While 1500W is the most popular heater size, it may not be the best for you. The following is a general guideline for heaters according to room dimensions.
A 200W inverter will also run fine if it is the only load. If you add a microwave or another appliance, you have to increase the inverter capacity. But provided it is only the heater, the system will run.
|Room Size||Heater Size||Inverter Size|
|50 sq. ft. = 500W||500W||750W|
|75 sq. ft. = 750W||750W||1000W|
|100 sq. ft. = 1000W||1000W||1500W|
|150 sq. ft. = 1500W||1500W||1500-2000W|
These sizes do not account for temperature or other factors. If there are several people in the room the temperature will go up, but if there is a cold draft somewhere the temperature drops. These and other factors affect heater performance.
Other heater sizes follow the same rule, add a few hundred watts to the inverter size for safety. For a 1000W heater, use a 1500W inverter, for 400W heater, a 750W inverter is sufficient and so on. Just get the next largest inverter size available.
Guidelines on Inverter Sizes
These inverter specs are the recommended size. They are not the bare minimum so you do not have to worry about system overloading. However in the real world it is unlikely you will use the inverter solely for a heater. At the bare minimum you also have to use lights and a few other amenities.
If you add lights and other appliances, 2000 watts might not be enough. That is why a 3000W inverter is sometimes used to run a 1500W heater. 2000 watts is enough for the heater, but add the other appliances and you need more power. You can use a 1500W inverter, but you have to know its limitations.
Plan ahead when calculating heater power use. Temperature changes, so some days you will be running the heater more, and other days for just a few minutes. You have to make allowances and be flexible with the sizing.
Which Inverter Should You Use For Heaters?
A pure sine wave inverter provides better performance than a modified sine. Pure sine inverters are more efficient in preserving energy so heaters have more power to use.
To run a heater on an inverter, it must be connected to a battery or another power source. The inverter converts DC power to AC so the heater can use it. During the conversion, energy is lost, and this is called inverter inefficiency.
Inverter ratings are based on how well it reduces energy loss. Most inverters are 85% efficient, meaning 15% power is lost. Newer inverters have a 95% efficiency rating, and these are mostly pure sine.
Modified sine wave inverters do not handle power losses as well as pure sine. In fact older models lose as much as 30%. If you want to use as much power as possible for your heater, pure sine wave systems are the best option.
Buying a pure sine wave inverter is an investment. It costs more than a modified sine, but the extra power available makes a big difference. This is especially important for a power hungry device like a heater.
Pure sine wave inverters are also ideal for modern appliances. Modern appliances are more energy efficient than ever, but this is only as good as the inverter you connect them to. If you have a modified inverter with 30% energy loss, the efficiency is wasted.
How Long Can an Inverter Run a Heater?
Heaters should not be left to run 24/7. Leaving it on for such long periods is dangerous and unnecessary. The room dimensions, your comfort level and atmosphere determine how long a heater should run and how much power it uses up.
A 2000W inverter powered by a 400ah battery bank can run a 1500W heater for 2 to 3 hours, which is enough time to warm up a 500 sq. ft. room. A smaller area requires less power to run, though the ambient temperature is a factor.
You can combine two 200ah batteries like the Mighty Max 12V AGM and get 400ah. This is enough to keep the heater going for the period given above.
The longer you run a heater, the more power the inverter needs to draw from the battery or generator. If you have a 1500W heater but only run it for an hour, power consumption will be lower compared to our example.
So while a heater needs as much power as running an AC on solar, you will be using it less. this also means you have to adjust your calculations because it might vary day to day.
On some days for instance you may need to run the heater a couple of hours to warm your room. A few days later the temperature might be higher, so you run the heater for just 30 minutes. But it never comes to a point you have to leave the system on 24/7.
As long as the inverter can handle the heater power requirements, it will not be a problem. It is the batteries that will determine how long you can run the heater. Whether it is a space heater or water heater, their amps must be appropriate for the battery.
To keep things simple, you only need to run a heater 2 to 3 hours at a time. All you need is a battery bank that can deliver the needed power to the inverter. And that is what we will explain next.
What are the Best Batteries For Heaters?
Without electrical power, an inverter needs a battery bank to run something as powerful as an inverter. How much depends on the following.
To run a 1500W heater for two hours on a 2000W-3000W inverter, two 350ah 12V batteries are needed. This is based on the assumption the batteries are FLA with a 50% depth of discharge and there are no other loads.
FLA, AGM and gel batteries cannot be used to full capacity. Once the level drops to 50% you have to recharge it. A 350ah 12V battery is 4200 watts, but only 2100 watts can be used by the inverter.
Our heater consumes 1500 watts an hour so it needs 3000 watts. Two 350ah batteries gives you 4200 usable watts. Just like solar panels, it is better to have a few more hundred watts available so 4200 watts is right.
Can you use FLA batteries beyond the 50% discharge rate? Yes, and the battery will not die right away. But over the long term, discharging below 50% is going to wear it down. That is why solar power users suggest to stick with the 50% mark. When recharging, stop at 85% because charging up to 100% is not good either.
If you want to use full battery capacity, get a high end AGM battery bank which can go up to 70%. Or better yet a lithium battery bank. Lithium batteries cost a premium but usable power can be 100%. You have to choose between these types and you must never combine them in a single battery bank.
Tips to Reduce Heater Inverter Power Consumption
While heaters have become more energy efficient, there are still ways you can reduce power consumption even more.
Use the right size. Follow the guide we have above to help you choose the right inverter and heater pair. You do not want a heater that is too small, but if it is too large you will be wasting power. By using the right heater for the right room, you get optimum results.
Buy a heater with the right features. A timer is required in case you forget to turn the system off. A digital thermostat adjusts the temperature so you are kept warm without using too much power. There should also be a saving or economy mode to reduce power consumption.
Wear warm clothes. Sounds simple but effective. Putting on multiple layers of clothing or wear something made from thick fabric should keep you warm.
Fix any gaps and cracks in the house. You should do a thorough checkup of your home and do repairs before the cold season. Insulate your home as best as you can, and the heater will do less work.
Lastly, buy from a quality manufacturer. This applies to both the heater and inverter. You can only go so far unless you buy products that are designed to last. Knowing how long the inverter can last is also crucial.
Running a heater on inverters and solar PV systems is similar to a refrigerator or AC. It is going to use a lot of power so your system has to be up to the task. But with the right information and knowledge it is possible and can be done for as long necessary.