Fireplace Sizing Guide: What Size Fireplace Do I Need?

Choosing the right size fireplace is the most important decision you will make. Too small and it will struggle to heat your room on a cold Highveld night. Too big and you will end up burning it low, which wastes wood, blackens the glass and builds up soot in the flue. This guide shows you how to work out the heat output you need in kilowatts (kW).

Fireplace Size Chart

Looking for a built-in unit? Use the same sizes on our built-in wood fireplaces page – the Heat Output filter in the sidebar works the same way.

How to Work Out Your Fireplace Size

1. Measure the room. Multiply the length by the width to get the floor area in m². If the room is open-plan, include every area that is open to it, such as the dining room and kitchen.
2. Apply the rule of thumb. Divide the floor area by 10 to get a starting point in kW. For example, 7m × 8m = 56m², so about 5.5–6kW.
3. Adjust for your home. Use the factors below to move up or down a size.
4. Choose from the right band. Pick a fireplace whose nominal heat output falls in your range.

When to Go Up or Down a Size

Go up a size if:

• Your ceilings are higher than 2.7m or the room is double volume
• The house has little or no ceiling insulation
• There are large windows, sliding doors or stacking doors
• You want the fireplace to help heat rooms beyond the one it is in
• The room has tiled or concrete floors and gets little winter sun

Go down a size if:

• Your home is well insulated, with double glazing or a north-facing room that gets winter sun
• The room is closed off from the rest of the house
• You mainly want ambience on cool evenings rather than full heating

Why Not Just Buy the Biggest Fireplace?

A closed combustion wood fireplace burns cleanest and most efficiently when it runs at or near its nominal output. If a fireplace is too big for the room, you will keep turning the air control down to stop the room overheating. A fire that is starved of air smoulders, which causes:

• Blackened glass and more smoke
• Faster soot and creosote build-up in the flue
• Wasted wood and lower efficiency

The right size fireplace burns brightly, keeps the glass cleaner and uses less wood.

Sizing Gas, Bio Fuel and Pellet Fireplaces

• Gas fireplaces – use the same kW rule of thumb. Check the heat output listed on each product and whether the model is flued or flueless, as flueless units have room-size requirements for ventilation.
• Bio fuel fireplaces – produce real flames and moderate heat. They are best for ambience and for taking the chill off smaller rooms rather than heating a large home.
• Pellet fireplaces – have adjustable output and a thermostat, so they can run efficiently across a wider range. Size them using the same chart.

Frequently Asked Questions

What size fireplace do I need for a 50m² lounge?

About 5–8kW. Start at around 5–6kW for a well-insulated room with a standard ceiling, and move towards 8kW if the ceiling is high, the room is poorly insulated or it opens onto other areas.

What size fireplace do I need for a 100m² open-plan area?

About 10–12kW for an average home. If the space is double volume or has a lot of glass, look at 12–14kW.

How many kW do I need per square metre?

Allow roughly 1kW for every 10m² of floor area with a ceiling height of 2.4–2.7m, then adjust for insulation, ceiling height and how open the space is.

Does a bigger fireplace heat better?

Not necessarily. An oversized wood fireplace has to be turned down, which makes it smoulder, blacken the glass and waste wood. Choose the size that matches your room.

Can MultiFire help me choose?

Yes. Send us your room measurements and a few photos, call 012 492 9834, or visit our showroom in Centurion for expert advice.

This guide gives general guidance only. Your exact requirements depend on your home's layout, insulation and local climate. Always follow the manufacturer's installation instructions and local building regulations.