What size 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:

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:

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.

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.