What size heater do you need?

Anula Wiwatowska
Jul 08, 2024
Icon Time To Read3 min read
// Brrr, its cold in here

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Every room has different heating requirements, and while there are several contributing factors the first thing to consider is how big of a heater do you need? Generally speaking the higher the wattage, the more powerful the heater, and the larger space it can adequately cover. But electric heaters and gas heaters aren’t created equal, and then there’s insulation, window size, and climate zones to consider too.

In this guide we’ll walk you through the basics of how to pick the right size heater for your home, and what else might be shivering your timbers.

The basics

No matter what kind of heater you’re using, you’ll need to know the square meterage of the room you’re looking to heat up. Measure the length and width of the room and multiply them together to find out the size of your room in square metres. Provided you don’t have exceptionally high ceilings (ie taller than 2.4m2), then this number should give you a good indication of what kind of wattage your heater requires.

What size electric heater do you need?

Electric heaters have a simple coverage formula: 1000W covers around 10m2. So at the most basic level, a 2.5m x 2.5m room should be serviced by a 1000W electric heater. Electric space heaters tend to tap out at around 2400W, so this should be enough to cover around 24m2 or a 6m x 4m room.

Here are some of the most common wattages you’ll find on electric heaters, and how much space they cover:

Coverage (m2)

What size gas heater do you need?

While electric heaters are reasonably straightforward, gas heaters’ coverage varies depending on the climate zone you live in. The colder the temperate zone, the smaller coverage the same heater can cover.

Even though most gas heaters are measured based on their Megajoule (Mj) usage, to accurately look at coverage you’ll need to consider the KW output instead. On average 1kW (1000W) of heating power from an indoor gas heater covers 8.65m2, but it can be up to double that in Mild Zones. Outdoor heaters are a whole other ballgame! Here are how the different zones compare:

Climate zone
Coverage per 1000w (m2)
Very cold zone8.5
Cold zone10
Cool Zone13
Mild zone16

You can probably guess how these four zones split up across the country. Mild zones are up top closer to the equator, and Very cold zones are down in Tasmania and other snowy regions across the country. Australia is split into eight different climate zones according to Australian Building Codes which are divided out in the map below. The white and dark blue areas are Very Cold Zones, the green and light blue are Cold, the beige and orange are Cool, and the yellow and dark orange are Mild.

Australian climate zone maps

Other considerations

As I said at the top, these room sizes are a general estimate but there are a whole heap of other considerations that can affect how well your heater will actually warm a room. Things like abnormally high ceilings, large windows, poor insulation, foundation type, and flooring type can make a room harder to heat up (or cool down for that matter). 

For each of the following factors, your heater will lose around 5% efficiency;

  • House built on pillars instead of a concrete slab
  • Hard flooring instead of carpet
  • No window coverings
  • Ceilings exceeding 2.4m

If you don’t have roof insulation then you’ll lose a full 10% of power on top of that. Because of how older Australian homes were built, you could easily be looking at more than a 50% reduction in efficiency before even factoring in leaky doorways and windows.

Blocking up doorway gaps will help quite a bit, but glass is a poor insulator, so large windows can make rooms harder to keep warm. Each square metre of window requires an additional 62W of power to warm up the space, which can add up quickly if you’ve got a lot of natural light. 

It’s not all doom and gloom though, there are a handful of ways that you can maximise your heater wattage. Block off leaky doors and windows with window seals, add rugs to hard floors, and get some dense window coverings.

Anula Wiwatowska
Written by
Anula is the Content and Social Media Editor within the Reviews.org extended universe. Working in the tech space since 2020, she covers phone and internet plans, gadgets, smart devices, and the intersection of technology and culture. Anula was a finalist for Best Feature Writer at the 2022 Consensus Awards, and an eight time finalist across categories at the IT Journalism Awards. Her work contributed to WhistleOut's Best Consumer Coverage win in 2023.

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