Buying a fireplace that is too small is frustrating. You will run it flat out and still feel cold corners of the room. Buying one that is too big is worse. You end up running it at low output most of the time, which produces more smoke, burns more wood per kilowatt of heat, and shortens the life of the heater.
Sizing a fireplace properly comes down to a simple calculation, but with a few Australian-specific factors most online guides miss. This is the same approach we use when sizing units for customers in our showrooms. If you're still deciding which type of fireplace is right for your home, start by reading our guide on choosing between wood, gas, and electric before selecting the correct size.
The Quick Rule: 1 kW Per 10 to 14 Cubic Metres
Here is the working rule for an Australian home with average insulation.
Measure your room volume in cubic metres (length × width × ceiling height in metres). Divide that number by:
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14 for a well-insulated modern home with double-glazing
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12 for a typical Victorian home with standard insulation
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10 for a poorly insulated home, an older weatherboard, or anything with single glazing
The result is the minimum kilowatt heat output you need. Round up to the nearest available size.
A worked example
Say you have an open-plan living and dining area that is 8 metres long, 6 metres wide, with a 2.7 metre ceiling. That is 8 × 6 × 2.7 = 129.6 cubic metres.
If your home is a 1990s build with batt insulation and standard glazing, divide by 12: 129.6 ÷ 12 = 10.8 kW. You want a heater rated at 11 kW or higher.
If your home is a modern build with double-glazing and good insulation, divide by 14: 129.6 ÷ 14 = 9.3 kW. A heater rated at 9 to 10 kW will do.
If your home is older, poorly insulated, or has high ceilings or single glazing, divide by 10: 129.6 ÷ 10 = 12.96 kW. You want 13 kW or more.
The Five Factors Most Guides Miss
1. Ceiling height matters more than people think
Heat rises. A 2.4 metre ceiling and a 3.5 metre cathedral ceiling in the same square metre room are very different heating jobs. The cubic metre calculation handles this, which is why we always size by volume, not floor area.
2. Open-plan layouts versus closed rooms
If your living room opens directly into the kitchen and dining, the heater is effectively heating all three rooms. Add their volumes together in your calculation. The trade-off is that the heat distribution will not be even. The room with the fire will run hottest.
3. Stairwells and double-storey homes
If your living room has a stairwell or void, you are heating the upstairs too whether you want to or not. Add the upstairs landing or hallway volume to your calculation. Otherwise the heater will struggle to maintain temperature on the ground floor.
4. Heat loss surfaces
Large north-facing windows are heat assets in winter (passive solar gain during the day). Large south-facing windows are heat losses. Concrete slab floors absorb heat into thermal mass. Carpeted timber floors insulate well. None of these change the volume calculation but they change how the heater performs in practice.
5. Your tolerance for being too warm
Most installers and showrooms slightly oversize because customers complain more about a cold heater than a warm one. When you're between two sizes, the best choice depends on your home's insulation, ceiling height, and how you plan to use the fireplace. Rather than automatically choosing the larger model, we assess your home's layout and heating requirements to recommend a heater that delivers efficient, comfortable warmth without being oversized.
Quick Reference: Heater Size by Home Size
Small living room (up to 30 sqm, 2.4 to 2.7m ceiling)
3 to 6 kW heater
Suitable for: bedrooms, studies, second living rooms, smaller cottages
Medium room (30 to 50 sqm, standard ceiling)
6 to 9 kW heater
Suitable for: average suburban living rooms, smaller open-plan zones
Large room (50 to 80 sqm, standard ceiling)
9 to 13 kW heater
Suitable for: most three-bedroom homes' main living areas
Very large room or whole house (80 to 150 sqm)
13 to 18 kW heater
Suitable for: large open-plan family homes, whole-house heating from one zone
Cathedral ceilings or very poorly insulated
Add 2 to 4 kW to the size you would otherwise pick
Suitable for: warehouse conversions, federation homes, holiday homes
Once you've determined the right size, the next step is understanding installation costs and requirements. Our Fireplace Installation Cost Guide explains what to expect.
Sizing Differences by Fireplace Type
Wood heaters
Wood heaters scale from about 5 kW to 25 kW. They are the most versatile sizing-wise, which is why they are the default choice for whole-home heating. A 15 kW wood heater can comfortably warm most three-bedroom homes from a single living room location. Once you've calculated the heating capacity you need, compare our range of wood heaters by kW output to find models that suit your home.
You can also explore the Australian Home Heating Association website for additional information about certified wood heaters and heating performance.
Gas log fires
Gas log fires typically scale from 4 kW to 9 kW. This makes them ideal for single rooms and open-plan zones, but a single gas log fire will struggle to heat a whole large home. If you want gas heating across multiple zones, you will need multiple units or supplementary heating. If gas is the right choice for your home, compare our range of gas log fires by heating capacity to find a model suited to your space.
Electric fireplaces
Most electric fireplaces top out at around 2 kW. They are not designed to be the primary heat source for a room over 30 square metres. They work brilliantly alongside reverse cycle air conditioning for ambience and supplementary heat. Do not buy an electric unit as your main winter heater unless your space is very small or you have other heating already.
Don't Oversize As Insurance
The temptation when you have a bigger budget is to buy a bigger fireplace just to be safe. This usually backfires for three reasons.
Wood heaters run dirty when undersized for their load
If you have a 20 kW wood heater in a room that only needs 10 kW, you will end up running it on low burn most of the time. Low burn produces more smoke, deposits more creosote in the flue, and reduces overall efficiency. It also annoys your neighbours and gets you flagged by council on high pollution days.
Gas log fires waste fuel when oversized
A bigger gas log fire uses more gas per hour. If you only need 4 kW of heat output and you buy a 7 kW unit, you will pay for gas you do not need. Modern thermostatic units mitigate this somewhat, but you are still paying upfront for capacity you will not use.
Bigger units cost more upfront
Larger-capacity fireplaces generally cost more than smaller models, and they may also require larger flue systems or additional installation work depending on the application. If your home doesn't need the extra heating capacity, choosing an oversized unit can mean paying more upfront without seeing a meaningful improvement in comfort or efficiency.
As fireplace pricing varies between manufacturers, models, and suppliers, we recommend selecting a heater based on your home's heating requirements first, then confirming current pricing with your local Evolution Fires showroom before making a final decision. For more advice on improving home heating efficiency and reducing energy use, Sustainability Victoria provides practical guidance on choosing efficient heating solutions.
How We Size Heaters In Our Showrooms
When customers come to one of our showrooms, we ask five questions before recommending a size.
1. How big is the room you want to heat? Length, width, ceiling height.
2. Is the room open to other parts of the house, or closed in?
3. What is your home built from? Brick, weatherboard, double brick, lightweight construction?
4. Do you have double-glazing or single-glazing?
5. Are you trying to heat one room or the whole house?
Those five answers usually narrow the choice to two or three units. If you want a hand sizing a unit for your specific home, book a free in-home consultation and we will measure the space and run the calculation for you.
Book a Free Sizing Consultation
Getting the size right makes the difference between a fireplace you love and one you regret. If you'd like personalised advice, book a free in-home sizing assessment and we'll measure your space and recommend the most suitable fireplace.
Geelong: 304 Melbourne Rd, North Geelong | (03) 5272 2587
Ballarat: 845 Howitt St, Wendouree | (03) 5338 2586
Traralgon: 194 Argyle St, Traralgon | (03) 5149 0344
