Boiler Power per Square Meter: Complete Sizing Guide (2026)
Which is the best wood boiler? Which is the best pellet boiler? And which is the most economical biomass boiler? These are among the most common questions we receive at our technical support.
The honest answer: there is no single “best” or “most economical” boiler that fits everyone. Each installation has its own characteristics, floor area, building insulation, climate zone, domestic hot water requirements, radiator type, ceiling height, and budget. A 30 kW boiler that is ideal for a 150 m² home in Athens with good insulation will be undersized in an identical 150 m² home in northern Greece with old windows.
The right boiler is the one that fits your need.
The following guide shows how to select the correct power per square meter, with cost tables and specific Axinar pellet and wood boiler models from 20 to 250 kW.
- 100 m² → 12-18 kW
- 120 m² → 15-22 kW
- 150 m² → 18-27 kW
- 200 m² → 25-36 kW
- 300 m² → 36-54 kW
Actual values depend on insulation, zone, ceiling height, and domestic hot water needs.
How to Calculate Boiler Power
The basic calculation formula is:
Power (kW) = Area (m²) × Coefficient (kW/m²)
The coefficient depends on two main factors: building insulation and climate zone.
Insulation coefficients
| Building type | kW / m² |
|---|---|
| New construction, energy class A+ (KENAK) | 0.08 – 0.10 |
| Well insulated, energy class B | 0.10 – 0.13 |
| Medium insulation (homes built 1990-2010) | 0.13 – 0.17 |
| Old construction, no insulation | 0.18 – 0.25 |
Greek climate zones
| Zone | Regions | × |
|---|---|---|
| A (southernmost) | Crete, Rhodes, Aegean islands, Laconia | 0.85 |
| B | Attica, Peloponnese, S. Epirus | 1.00 |
| C | Thessaloniki, Central Macedonia, Thessaly | 1.10 |
| D (northernmost) | W. Macedonia, mountainous Epirus, Drama, Evros | 1.25 |
Sample calculation
Home 150 m², medium insulation, Thessaloniki (Zone C):
- Base power: 150 × 0.15 = 22.5 kW
- With zone C: 22.5 × 1.10 = ~25 kW
Recommended models: Axinar PELIT PL30 (30 kW), 1.768€ or Axinar BM30 Wood (30 kW), 2.170€.
Pellet Boilers, Selection Table
Pellet boilers have stable efficiency of 90-93%, so theoretical power translates to actual heating. Axinar produces three lines:
- PELIT: base boiler (burner sold separately)
- PelletWork (PW): integrated system with built-in burner
- CALOS: all-in-one with automatic cleaning, ideal for small installations
| Area | Power | PELIT (base) | PelletWork (integrated) |
|---|---|---|---|
| 60-100 m² | 8-20 kW |
CL8–32
3.651€
|
PW20
2.666€
|
| 100-150 m² | 20-30 kW |
PL20
1.711€
|
PW20
2.666€
|
| 150-220 m² | 30-45 kW |
PL30
1.768€
|
PW30
2.852€
|
| 220-330 m² | 45-75 kW |
PL45
1.953€
|
PW45
3.224€
|
| 330-500 m² | 75-95 kW |
PL75
2.703€
|
PW75
4.650€
|
| 500-700 m² | 95-120 kW |
PL95
6.396€
|
PW95
?
|
| 700-900 m² | 120-150 kW |
PL120
5.112€
|
PW120
7.914€
|
| 900+ m² (commercial) | 150 kW |
PL150
5.683€
|
PW150
9.284€
|
Wood Boilers, Selection Table
Wood boilers have slightly lower average efficiency (80-88%), so we typically choose 10-15% higher power than the pellet equivalent. Axinar produces:
- BM: base wood boilers
- BM_e: with lambda sensor and advanced software for precise combustion control
- PESKON: with integrated heat exchanger, economical solution
| Area | Power | Economical | Standard | Advanced (λ-sensor) |
|---|---|---|---|---|
| 100-150 m² | 25-35 kW |
PSK30
1.625€
|
BM30
2.170€
|
— |
| 150-250 m² | 35-60 kW |
PSK60
1.897€
|
BM60
2.666€
|
— |
| 250-400 m² | 60-95 kW | — |
BM90
2.852€
|
e_BM_e90
8.928€
|
| 400-700 m² | 95-150 kW | — | — |
e_BM_e150
14.880€
|
| 700-1200 m² (commercial) | 150-250 kW | — | — |
e_BM_e250
24.800€
|
Factors that Change the Required Power
1. Ceiling height
Standard calculation assumes 2.8-3 m ceiling. For higher:
- 3-3.5 m → +10%
- 3.5-4 m → +20%
- 4+ m (loft, hall) → +30-40%
2. Domestic Hot Water (DHW)
If the boiler will also supply DHW (bathroom/kitchen), add ~5 kW for 2-4 people. For larger families or boiler tank ≥ 200L, +8-10 kW.
3. Floor Heating vs Radiators
- Underfloor heating (~40°C): better efficiency
- Radiators (~60-70°C): standard calculation
4. Building exposure
- Mountainous / exposed slope: +15%
- Dense apartment building / middle floors: -10%
5. Window age
Old wood or aluminum → +10-15%. Modern energy-efficient (double glazing) → -5%.
What if I Choose a Boiler Bigger than I Need?
Many installers traditionally suggest “get slightly bigger for peace of mind”. This was bad practice. For modern modulating boilers:
- On/off cycling: more frequent starts + shutdowns = wear on electronics and chimney
- Lower efficiency: rarely operates at nominal power
- Higher consumption: not less, on the contrary
- Higher purchase and maintenance cost
Modern Axinar pellet boilers have 30-100% modulation, adapting power to demand without unnecessary cycles.
Frequently Asked Questions about Boiler Power
Need help choosing the right boiler?
Axinar manufactures pellet and wood boilers from 8 to 250 kW, all with EN 303-5 Class 5 certification and 5-year warranty.
