May 2, 2025

What Size Log Burner Do I Need? A Simple Guide to Finding the Perfect Fit

Not sure what size log burner you need? If your last fire left you sweating in shorts—or shivering in a parka—you’re not alone. Short answer: measure your room (in m³) and divide by 14 for the ideal kW output. Keep reading to discover what log burner to buy and why size really matters!

Understanding Heat Output (kW) and Room Size

When it comes to log burners, size really does matter—but not in the way you might think. It’s not about the stove's physical dimensions, but about how much heat it generates, measured in kilowatts (kW). If you pick the wrong size, your room could end up feeling like an oven or, worse, like a freezer.

So how do you work out what’s right for your space? Let’s dive in!

Calculating Your Room's Volume (Length x Width x Height)

The first step is to calculate your room’s volume. Grab a tape measure (don’t worry, this part’s easy) and measure your room’s length, width, and height. Then simply multiply them together to get the room’s volume in cubic metres (m³).

For example, let’s say your room is 5 metres long, 4 metres wide, and 2.5 metres high. That gives you a total volume of:

5 × 4 × 2.5 = 50m³.

Once you have that number, divide it by 14. This gives you a rough estimate of the kW output your stove should have. In this case:

50 ÷ 14 = approx. 3.6 kW.

This formula is a great starting point, but there are a few more factors to consider. Let's take a look!

General Guidelines for kW Output per Room Volume

Now that you know how to calculate your room’s volume, here’s a rough guide for choosing the right stove based on room size:

2–4 kW: Best for small rooms or well-insulated modern spaces (up to 30m³).
4–6 kW: Ideal for medium-sized living rooms (30m³–50m³).
6–8 kW: Great for larger rooms or older homes with poor insulation (50m³–70m³).
8 kW or more: Only needed for very large spaces, or rooms with poor insulation (70m³+).

Remember, if you’re in doubt, it’s always better to slightly overestimate than risk ending up cold. After all, you can always open a window to cool down if things get too hot.

Other Factors Affecting Heat Requirements

Not all rooms are created equal. While the formula is a great guide, there are other things to think about—such as how well your home holds onto heat, and where your room is located. Let’s break them down.

Insulation Quality (Walls, Roof, Windows)

If your home is old and drafty, you’ll likely need a larger stove to compensate for heat loss. Well-insulated homes, on the other hand, retain heat much better, meaning you can get away with a smaller stove.

Think of it this way: if your room’s as airtight as a thermos, a small log burner will do just fine. But if your room feels like a wind tunnel in winter, you’ll need more heat to make up for all that warmth escaping through the walls, roof, or windows.

Number of External Walls

The more external walls your room has, the more heat it loses. Rooms with two or more outside-facing walls are particularly susceptible to heat loss, so you might need a slightly larger stove for these spaces.

For instance, a corner room with three external walls will need more power than a room with just one external wall. The heat simply has to work harder to stay inside.

Glazing Area

Large windows, or a room full of glass, can be a beautiful feature, but they’re not so great when it comes to holding heat. Heat escapes much more quickly through glass than through walls.

If your room is full of large windows or has French doors leading outside, consider a stove with a higher kW output, as your room will lose heat more quickly.

Room Location (e.g., exposed corner)

The location of your room also plays a big role. Rooms in exposed corners or with lots of external exposure, like those on the north side of the house, often need more heat to maintain a comfortable temperature.

Similarly, high ceilings or open-plan spaces may require more heat to keep everything warm. Heat tends to rise, so you might find that a larger stove is needed to circulate warmth throughout the space.

Avoiding Oversized and Undersized Burners

While it might be tempting to go for the biggest stove available, bigger isn’t always better. Picking the wrong size can lead to some serious issues—whether your stove is too big or too small.

Problems with an Oversized Burner (Overheating, Inefficient Burning)

A stove that’s too big for your room will overheat the space, and not in a cosy way. The room will become unbearable, and you’ll end up opening windows to cool down. But that’s not the worst part.

Running an oversized stove on low is inefficient. It leads to poor combustion, which means smoky glass, a sooty flue, and wasted fuel. You’ll spend more on wood, and your stove’s performance will suffer.

Problems with an Undersized Burner (Insufficient Heat)

On the other hand, a stove that’s too small won’t be able to heat your room effectively. You’ll spend hours trying to get warm, constantly stoking the fire and refuelling. The heat will never quite reach a comfortable level, leaving you cold and frustrated.

If you find yourself constantly adding logs and the room still feels chilly, it’s time to rethink the size. An undersized burner may be causing more stress than comfort.

Using Online Calculators and Seeking Professional Advice

If you’re still unsure about what log burner to buy, online calculators can help you get a quick idea of what size stove you need. Many manufacturers offer online tools where you can input your room’s measurements and get a recommended kW output.

However, an online calculator is just a rough estimate. For a more accurate recommendation, it’s always best to consult a HETAS-registered installer. These professionals can assess your room in person, check your flue setup, and advise you on the best stove for your home.

It’s worth investing in expert advice—after all, it’s better to get it right the first time than deal with the hassle of returns or, worse, a chilly winter.

Final Thoughts: Size Really Does Matter

Choosing the right size log burner is key to getting the perfect warmth without the hassle. Stick to the formula, consider all the factors, and don’t forget to account for your home’s unique quirks.

Whether you’re shopping for a small room or a grand open-plan space, the right stove will keep you cosy without the risk of overheating or underheating your space.

Ready to find your perfect fit? Start with the measurements, and talk to an expert if you’re still unsure. Your winter evenings just got a whole lot warmer!

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