A home generator is now essential for backup power in Australia, with increasing severe weather, natural disasters and an energy crisis in our power grid. But what size generator do you need for a house? It’s easy to overpay for too much generation you’ll never use. But undersize your generator and your appliances will trip it off annoyingly. In this post, we’re going to help you answer the most common questions about exactly what size generator you need for your house.

We will help you work out exactly what you need, for your circumstances. So you don’t over pay or run out of back up power.

What size generator do you need to run a house – a summary

The size generator you need to run a house is around 5,000 watts for basic necessities like refrigerator, Freezer LED lights, an LED TV, your internet modem, and a few laptops and mobile chargers. But there is no cooking or hot water in that list!

Add a cooktop and electric boosted gas hot water, and you will need more wattage. Around 8,000 watts should do the trick.

Add in an electric hot water system and you’ll need close to 15,000 watts!

Here is exactly what size generator you’ll beed for a 3 bedroom house, if you have one. It covers three options: a ‘budget option’, a ‘typical family’ and a ‘whole house’.

You’ll see below that the watts can add up quickly, and so too can the price.

That’s why it’s important to your hip pocket to ‘right size’ your home generator. And the exact size you need depends on the purpose of you generator and how much electricity you use.

Calculating the numbers out yourself can save you cash. We’ll step you through how to do this below.

But first, let’s answer some common questions about getting a generator for emergency power.

Why have a generator installed at your house?

Australia’s severe weather events commonly cause grid outages. Strong winds bring down power lines. Heavy rains and floods damage electrical infrastructure and disrupt your power requirements.

When the electricity goes out, so does your fridge, your lights, your internet, your cooking, and in many cases your hot water. If you are on tank water not town water, you’ll have no running water at all!

That’s why energy is an essential service for all Australians under Australia’s energy laws.

If you have a family, you know that having no power for 6 hours is tough to bear. But with the intensity of natural disasters increasing in Australia, comes a greater chance of blackouts or brown outs on a large scale.

Natural disasters that take down an entire neighborhood’s power grid can mean long-lasting power outages as electricity network operators struggle to fix the power grid and schedule thousands of reconnections.

From a simple wind storm in Tasmania in June 2022, we lost power to our home for 4 days.

The more severe the weather, the longer the blackout. The more frequent severe weather, the more often we’ll face these kinds of power outages.

In home generators grow in popularity

With more frequent weather related power outages and an energy crises on Australia’s east coast, house generators are growing popularity. This trend is not just in Australia. American families are turning to home generators to keep their houses running in response to climate change, mass power outages and general uncertainty about the future.

Particularly in disaster prone areas, Australians are increasingly choosing to mitigate the impacts of extreme weather power outages. Many are securing their own power supply by installing a large portable generator or a conventional heavy duty home generator (with transfer switch) at their home.

A home generator can also be critical if you live in an off-grid rural area too. For some Australians, a generator becomes a life sustaining choice to run essential equipment like CPAP machines and other medical devices.

A common question when it comes to home generators is Can I power multiple home appliances or indeed your whole house with a generator?

What size generator do you need to run a house, even?

Let’s take a look.

Can you power your whole house with a generator?

Yes you can power your whole house with a generator. But it’s going to be an expensive outlay to power every appliance in your home. The size of the generator determines much of its purchase price and (for traditional fuel generators) its running cost.

An online search for home generator will reveal different size traditional generators with different peak and rated output. It is important to your hip pocket that you choose one that can handle the wattage you need at your home. A home generator can run your whole house if you have the right size and model.

Having the right generator will also save you money.

Household appliances and electric equipment all require different amounts of wattage to operate. So you need to work out what household appliances, portable appliances and electrical tools you want to run in a black out.

Then you can choose what size generator will be right for you.

How do I calculate what size generator I need?

The first question, when looking at home generators is often ‘how big a generator do i need for my house?’.

Well, you can calculate it for yourself. Let’s show you how.

Firstly, it’s important to know that not all generators are created equal. With traditional fuel generators, the generator ‘peak power’ and ‘rated output’ determine how many essential appliances it can power at once.

For example, a small size diesel generator might be able to power a few lights and a refrigerator, while a larger size generator could run an entire house.

Instead of pulling out all of the appliances in your home to check the nameplate, appliance wattage estimates can be a useful guide. Check out our free Appliance Wattage Cheat sheet if you want to save time and hassle by using our estimates.

If you’re considering buying a generator to power your home, it’s important to determine what size and type is right for you.

Getting the wrong size home generator can be costly.

A smaller generator will be unable to run all of your devices and appliances and will trip off constantly. On the other hand, a large generator will be less efficient and cost more to buy and operate.

How to calculate generator size using ‘starting watts’ and ‘running watts’

So, how do you determine what size home generator you need for your circumstances?

You need to look at your ‘peak power requirements’ and the generator’s peak power and rated output.

To determine your peak power requirements, the first step is to calculate your total running wattage of the appliances, tools, electric motors you want to power.

‘Running watts’ is the total amount of energy that your devices and appliances will use when they are running continuously. To calculate this, simply add up the wattage of all devices and appliances that you want to run simultaneously.

Once you know total running watts, you need to find the highest starting wattage from your list of appliances. ‘Starting watts’ is the amount of electricity that is required to start up your appliances.

At initial startup, some appliances (especially motors, compressors and heating elements) need more energy. Therefore their starting wattage is higher than running wattage. So it’s important to factor in start up and starting watts when selecting a home generator.

You then need to combine your highest starting watts figure and your total running watts figure to get your total power requirements (peak power needs). Let’s look into what this means.

How generators are sized

After you have added up your starting and running wattage figures, you can choose a home generator size that meets or exceeds these values.

Standard generators that run on fuel have a “AC output” between 1000-12,000 watts. You need to look at the ‘total power output’ (or peak output) of the generator, as well as it’s ‘rated output’ (output while running).

For home generators that run on electrical energy, like solar powered generators or portable power stations, the peak output is often called ‘maximum output’. The rated output is often called ‘power capacity’.

Here are 2 rules of thumb for working out the best generator size for you:

1. The generator’s ‘peak output’ (maximum output) should be larger then your peak power requirements at any one instant.
2. The generator’s ‘rated output’ (power capacity) should be large than the total running watts of your appliances.

Often, fuel-based generator power is measured in ‘kVa’. So you will need to convert your power requirements in ‘watts’ into the equivalent ‘kVa’ measurement.

If you want to know more about how to use starting watts and running watts to work out your ‘peak power requirements’ and right sized home generator kVa, check out our generator sizing guide.

You can also use our free Generator Size Calculator. It will do all the numbers and conversions for you. You just need to input the watts you find on your home appliances!

Keep in mind that it’s always better to choose a generator rated slightly larger than what you need. Factoring in some extra watts will give you flexibility in terms of how you use power in a blackout.

So.. what size generator do you need to run a house?

The answer for most typical Australian homes is around 7,500 watts (7.5kW).

But that’s assuming you’re only running important load – things like your fridge, a freezer, a cooktop some lights, an LED TV and your internet – and maybe a few discretionary appliances. Let’s break down what size you might need, based on 4 real life scenarios:

1. Working from home emergency backup power – 1,000 watts
2. Critical household equipment – 5,000+ watts
3. Multiple appliances – 7,500+ watts
4. 24 hour+ blackouts – 10,000 watts
5. Heavy duty energy needs or long lasting blackouts – 12,000 to 20,000 watts

Let’s take a look at what you might be powering in each of these scenarios.

Work from home emergency backup

A lot of people work from home these days and still need to make a living with power supply disruptions. If this is you there is a relatively inexpensive solution. If you want uninterrupted power supply to your computer and the internet, a small inverter generator or small camping generators might be a low budget option.

For work from home backup power, aim for a 1,000 watt peak power generator to be flexible.

Critical household equipment

If you need a unit just to run your most critical household equipment like a fridge, freezer, LED TV, and lighting circuits choose one that has a peak power of at least 5,000 watts. Portable fuel based generators come in this size.

So do portable power stations. Portable power stations that run on lithium batteries are often expandable in size (power capacity) by adding another battery, so can definitely power your essential appliances.

Multiple appliances

For emergency situations, to run multiple home appliances for up to 48 hours, choose one that has a peak power of 7,500 watts. This will allow you to run things like a fridge, freezer, a cooktop, LED TV, portable devices and LED lights. But you will need to stage when you use these things (not run them all at the same time) so as not to overload the generator.

Extended blackouts

As a power outage continues, your power needs begin to grow. You need to wash clothes, recharge equipment, If you need a generator for extended outages and want more power, choose one that has a peak power of at least 10,00 watts. This will give you more flexibility to operate your home if you can afford this generator size.

There are portable power stations out there that expand all of the way up to 25kWh, which is plenty to run multiple appliances all at once for an extended time, in a blackout.

Heavy duty energy needs

If you need heavy-duty applications, like an electric hot water system (4000 watts), choose a generator size that has a peak power of at least 12,000 watts. In some cases, you may need to go as large as 20,000, although that will be some expensive backup power!

What size generator do I need to run my whole house with air conditioning?

To run whole house with air conditioning, the a recommended generator might be around the 20,000 watts (20kW) size.

It’s common in Australia to find 2kW (2,000 watt) air conditioners in each bedroom, and a 5 – 7kW air conditioner in the lounge room. That is going to take a lot of watts to power!

As we have explained above, in order to find out what size generator you need, you must first calculate the wattage of all the appliances.

The starting watts of an air conditioner can be 2 to 3 times its running watts.

That’s going to be an expensive generator to buy as well as to run. And that doesn’t even count running anything else in your household, like the fridge or lighting circuits for powering up computers and the internet.

This is why, for emergency preparedness many people opt for the right size generator for critical equipment only, rather running then all these appliances at once.

This is just a ballpark. Always follow these 6 easy steps to calculate what size generator you need.

Do you need an inverter generator?

When it comes to different types of generators, we’d recommend an inverter generator (for fuel-based models) to run sensitive equipment at home.

An inverter generator produces alternating current (AC) power. The AC power is then inverted to direct current (DC) power that runs most modern electronics.

Inverter generators that are designed to be more efficient than traditional ones are used to power sensitive electronics, such as flatscreen TVs. Inverter generators are also quieter and typically smaller than traditional generators.

Alternatively, you can also clean up the ‘dirty power’ produced by a conventional diesel generator by having an automatic voltage regulator installed with the generating unit.

Portable power stations have built in inverters and battery management systems that protect both the battery and your appliances from electrical damage.

How long can a generator keep a house running?

Conventional heavy duty generators can keep a house running for as long as there is fuel to power it.

The life expecting of a diesel generator can be up to 20,000 hours, depending on how it is run.

This means that if the unit is properly sized, and you have enough fuel, it can keep the lights on and appliances running for continuous long hours or days. If you have a transfer switch installed, you’ll barely be impacted when the grid goes down.

Of course, this assumes that the generator is well-maintained and there are no other issues that could cause it to fail. But if everything is working as it should, a heavy duty generator can provide a reliable backup source of electricity for many years.

Remember, in a prolonged power outage that it’s important to have a plan for refuelling the generator before it runs out of fuel. An emergency fuel supply at home is essential if you plan on installing and using a generator for emergency power supply over a period of days or weeks.

Conclusion

Increasingly, with extreme weather and general uncertainty about the future, Australians are starting to feel that it is worth the peace of mind knowing that they will have electricity when they need it most. But larger generators cost more to purchase and run. So in answer to the question “What size generator do you need to run a house?” we’d recommend 7,500 watts for a typical family home. But it’s important to your hip pocket that you calculate your specific power requirements before buying a generator. A lot of homes get away with smaller units at less cost by being selective about the power they use in time of emergency, and you can too!

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