Infrared Patio Heaters: How to Size Wattage and Number of Units (by Area)
This guide is about sizing: how much power (watts) you need for a given occupied area, and how many infrared heaters make sense. Infrared heaters are typically used for zone heating (a seating area, a table, a bar/standing spot), so the key input is the area people actually use, not the total patio size.
For outdoor zone heating, this guide uses a deliberately conservative minimum: 200 W per m² of occupied area. That avoids the common “on paper it should work” outcome that feels underpowered once you factor in mounting height, edge losses and light draughts.
UK units: We’ll use m² (common in UK product specs as “sqm”) and include ft² in brackets.
1 m² ˜ 10.8 ft².
Calculate the required wattage
Outdoor zone heating: minimum 200 W/m² (occupied area)
Formula:
Total power (W) = Occupied area (m²) × 200
So:
- 6 m² (˜ 65 ft²) ? 6 × 200 = 1200 W minimum
This baseline is intentionally conservative. Outdoor heating rarely happens in still air, and real seating layouts have edges that otherwise end up noticeably cooler.
Convert total wattage into the number of heaters
Total watts answer “how much”, but comfort depends on “how evenly”. A single heater often creates a warm centre and cooler edges, so the number of heaters is part of the sizing.
Practical rules of thumb:
- Up to 6 m² (˜ 65 ft²): 1 heater can work if it’s aimed well and the zone is compact
- 6–10 m² (˜ 65–108 ft²): 2 heaters are often better (more even comfort)
- 10–12 m²+ (˜ 108–129 ft²) or long/narrow zones: usually 2–3 heaters spaced along the area
Many UK electric infrared heaters are simply On/Off (some have steps; true dimming isn’t universal). If there’s no dimmer, using two smaller heaters gives practical control: one heater in milder conditions, both when it’s colder.
Worked example: 6 m² seating area outdoors (minimum 1200 W)
Occupied area: 6 m² (˜ 65 ft²)
Minimum power: 6 × 200 = 1200 W
Option A (one unit): 1× 1200–1500 W
Works if the heater is positioned so the main seats sit within the primary beam.
Option B (more even, no dimmer needed): 2× 600–800 W
Often better coverage across two sides of a table, and you can run one or both depending on conditions.
Quick sizing table (area? minimum watts? typical split)
Occupied area
4 m² (˜ 43 ft²)5
5 m² (˜ 54 ft²)7
6 m² (˜ 65 ft²)9
8 m² (˜ 86 ft²)
10 m² (˜ 108 ft²)15
12 m² (˜ 129 ft²)
15 m² (˜ 162 ft²)
Minimum outdoor power
800 W
1000 W
1200 W
1600 W
2000 W
2400 W
3000 W
Typical number of heaters
1
1
1-2
1-2
2
2
2
2-3
2-3
Typical split
1× 800–1200 W
1× 1000–1200 W
1× 1200–1500 W or 2× 600–800
2× 800–1000 W
2× 1000 W
2× 1200 W or 3× 800 W
2× 1500 W or 3× 1000 W
These are practical splits, not strict rules. Mounting height and aiming can change how strong it feels. But the table is reliable for purchase decisions: area ? minimum watts ? sensible distribution.
Worked example: 6 m² seating area outdoors (minimum 1200 W)
Occupied area: 6 m² (˜ 65 ft²)
Minimum power: 6 × 200 = 1200 W
Option A (one unit): 1× 1200–1500 W
Works if the heater is positioned so the main seats sit within the primary beam.
Option B (more even, no dimmer needed): 2× 600–800 W
Often better coverage across two sides of a table, and you can run one or both depending on conditions.
Optional: quick m² ? ft² cheat sheet
m²approx. ft²
4 43
5 54
6 65
8 86
10 108
12 129
15 162
No dimmer? How to control heat in daily use
Many infrared heaters are simply On/Off (sometimes with a few power steps, but not always). Do not plan your system assuming you can dim.
A practical solution is:
- use two heaters instead of one, or
- wire/switch them separately (if your setup allows it)
Then you can run:
- one heater in mild weather
- both heaters when it is colder
This gives you basic control without a dimmer.
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