Log Burner Size Calculator
A wood burning stove that's too small will never bring a room up to temperature, while one that's too large forces you to run it inefficiently just to avoid overheating. The right kW rating depends on your room's volume and how well it retains heat. Enter your dimensions below for a starting point when shopping for a stove.
Find the right stove size for your room
Enter your room dimensions and how well insulated the room is.
Typical older UK home with some draughts
For a 48.0m³ room, you need a stove rated at approximately:
4.0kW
Look for a stove rated around 4kW — stoves are usually sold in whole or half kW sizes, so round up rather than down.
Recommended products
A few well-reviewed log burners at a range of kW outputs.
- Small Rooms
£394.75
Pros
- Compact 5kW output suits smaller UK living rooms
- Airwash system keeps the glass door clear of soot
- DEFRA approved for use in smoke control areas
Cons
- Professional HETAS installation strongly recommended
- Smoke Control Areas
£1099.00
Pros
- DEFRA tested for use in smoke control areas
- Air-wash system keeps the glass door clearer for longer
- Ready to install with no assembly required
Cons
- Professional HETAS installation strongly recommended
- Fewer Amazon reviews than the longer-established Ekol Crystal
- Multi-Fuel
Currently unavailable
Pros
- External air supply option keeps the room draught-free
- Danish design and build quality with 80%+ efficiency
- Heats rooms up to around 150m³
Cons
- Professional HETAS installation strongly recommended
- Premium Danish styling costs more than budget cast-iron stoves
Frequently asked questions
Why does an oversized stove cause problems?
An oversized stove overheats the room quickly, forcing you to run it on a low, smouldering burn to compensate. Low, cool burns produce more smoke and tar, which builds up as creosote in the flue and increases the risk of a chimney fire — so bigger isn’t always better.
Do I need a survey before buying a stove?
This calculator gives a solid starting estimate, but UK building regulations and most installers will carry out a proper heat loss calculation before fitting a stove, factoring in wall construction, window area, and ceiling height precisely. Use this figure to shortlist stoves, then confirm with your installer.
What if the room is open-plan and connects to other rooms?
Add the volume of connected, open spaces to your total room volume before calculating, since heat will circulate between them. Just note the estimate assumes reasonably even airflow between the spaces.
Can a log burner heat more than one room?
Some stoves come with a boiler back that can feed radiators elsewhere in the house, but a standard stove primarily heats the room it sits in and adjoining open-plan space through air circulation.
How this calculator works
The calculator multiplies your room length by width by height to get the volume in cubic metres, then divides that volume by a divisor based on your insulation level. A well-insulated room divides by 14, an average room by 12, and a poorly insulated room by 10. The result is the approximate kW output needed. The calculator then rounds up to the nearest standard stove size from the range of 4-14 kW.
The insulation divisors are based on the rule of thumb that 1 kW of stove output heats roughly 14m³ in a well-insulated room, 12m³ in an average room, and 10m³ in a poorly insulated room. These are starting estimates only — actual heat loss depends on window size, wall construction, ceiling height and ventilation. Always confirm with a proper heat loss calculation before buying.
Typical log burner sizes and room coverage
| Stove size | Well-insulated room | Average room | Poorly insulated room | Typical use |
|---|---|---|---|---|
| 4kW | Up to 56m³ | Up to 48m³ | Up to 40m³ | Small bedroom, study, ensuite |
| 5kW | Up to 70m³ | Up to 60m³ | Up to 50m³ | Small living room, dining room |
| 7kW | Up to 98m³ | Up to 84m³ | Up to 70m³ | Medium living room, kitchen-diner |
| 9kW | Up to 126m³ | Up to 108m³ | Up to 90m³ | Large living room, open-plan space |
| 12kW | Up to 168m³ | Up to 144m³ | Up to 120m³ | Very large room, barn conversion |
| 14kW | Up to 196m³ | Up to 168m³ | Up to 140m³ | Large open-plan, commercial space |
Worked example: A 5m x 4m x 2.4m living room with average insulation
A living room 5m long, 4m wide and 2.4m high has a volume of 5 × 4 × 2.4 = 48m³. With average insulation (divisor 12), the required output is 48 ÷ 12 = 4.0 kW. The calculator would recommend a 5kW stove, since 4kW is the next standard size up from the calculated 4.0 kW.
If the same room were poorly insulated (divisor 10), the calculation would be 48 ÷ 10 = 4.8 kW, still rounding up to 5kW. If it were well-insulated (divisor 14), it would be 48 ÷ 14 = 3.4 kW, rounding up to 4kW. This shows why insulation matters: a well-insulated room of this size could use a 4kW stove, while a draughty one needs 5kW or more.
Common mistakes when choosing a log burner
- Buying the biggest stove that fits the fireplace. An oversized stove overheats the room, forcing you to run it on a low, smouldering burn. Low burns produce more smoke and tar, which builds up as creosote in the flue and increases chimney fire risk. Always size to the room, not to the aperture.
- Ignoring the room's heat loss profile. A room with large single-glazed windows, high ceilings, or external walls on two sides loses heat faster than the calculator's average suggests. If your room has these features, add 20-30% to the calculated kW or get a proper heat loss survey.
- Forgetting about ventilation. Modern wood burning stoves need a permanent air vent in the room to supply combustion air. If the room is airtight (common in new builds), the stove will starve for air, smoke, and be inefficient. Check building regulations for ventilation requirements before buying.
- Assuming all stoves of the same kW output are equally efficient. A 5kW stove with 80% efficiency burns less wood and produces more heat than a 5kW stove with 65% efficiency. Look for the EU efficiency rating (aim for 75%+) and check whether it's suitable for smoke control areas if you live in a city.
What to look for when buying a log burner
Efficiency is the most important spec after kW output. Modern stoves range from 65% to 85% efficiency — the higher the percentage, the more heat you get from each log and the less ash and smoke you produce. Look for an EU type approval label (EN 13240 or EN 16584) which confirms the stove meets emissions and efficiency standards. In smoke control areas (most UK cities), you need a DEFRA-exempt stove that can burn wood without producing excessive smoke.
Construction material affects heat output and durability. Cast iron stoves retain heat well and are durable, but they can crack if overheated. Steel stoves heat up faster and are often cheaper, but they can warp over time. Soapstone or granite surrounds store heat and release it slowly, giving a more even warmth over several hours after the fire has died down. For most UK homes, a cast iron or steel stove with a good warranty (5+ years) is the best balance of cost and longevity.
Finally, think about installation. A log burner needs a suitable hearth, a flue or chimney liner, and ventilation. Hearth construction must meet building regulations (typically 12mm thick non-combustible board extending 150mm in front and 300mm each side). If you don't have an existing chimney, you'll need a twin-wall flue system, which can add £500-£1,500 to the installation cost. Always use a HETAS-registered installer.
More questions answered
Why does an oversized stove cause problems?
An oversized stove overheates the room quickly, forcing you to run it on a low, smouldering burn to compensate. Low, cool burns produce more smoke and tar, which builds up as creosote in the flue and increases the risk of a chimney fire — so bigger isn't always better.
Do I need a survey before buying a stove?
This calculator gives a solid starting estimate, but UK building regulations and most installers will carry out a proper heat loss calculation before fitting a stove, factoring in wall construction, window area, and ceiling height precisely. Use this figure to shortlist stoves, then confirm with your installer.
What if the room is open-plan and connects to other rooms?
Add the volume of connected, open spaces to your total room volume before calculating, since heat will circulate between them. Just note the estimate assumes reasonably even airflow between the spaces.
Can a log burner heat more than one room?
Some stoves come with a boiler back that can feed radiators elsewhere in the house, but a standard stove primarily heats the room it sits in and adjoining open-plan space through air circulation.
How much wood does a log burner use?
A typical 5kW stove running at full blast for 4-5 hours uses roughly 2-3kg of dry wood (about 2-3 medium logs). At a moderate burn, it might use 1-2kg per hour. A full winter's heating with a wood burner in a typical UK home uses 2-4 cubic metres of dry logs, depending on how often it's used and the insulation level.
What's the difference between seasoned and kiln-dried logs?
Seasoned logs have been air-dried for at least 12-18 months and have a moisture content of around 20-25%. Kiln-dried logs are dried in a controlled kiln to under 20% moisture, usually 10-15%. Kiln-dried logs burn hotter, cleaner and more efficiently, but they cost more. For a stove used regularly, kiln-dried is worth the extra cost — it produces more heat per log and causes less tar buildup in the flue.
Do I need a chimney liner for my log burner?
If you have an existing chimney, it should be swept and inspected before installation — many old chimneys need a stainless steel liner to ensure proper draw and prevent fumes leaking into the house. If you don't have a chimney, you'll need a twin-wall flue system running from the stove to the outside. Building regulations require that any flue is correctly sized for the stove and installed by a competent person.
Can I use my log burner in a smoke control area?
Only if the stove is DEFRA-exempt (approved for burning wood in smoke control areas). Most modern stoves sold in the UK are DEFRA-exempt, but it's worth checking before you buy. In a smoke control area, you must burn only dry wood — wet or unseasoned wood produces too much smoke and is illegal. You cannot use a log burner to burn household waste, treated wood, or coal in a smoke control area.