How to Size an Infrared Heater: Watts and Number of Units by Area
This guide is only about sizing: how many watts you need for a given usable area, and how many heaters make sense. With infrared heaters, you usually heat a zone (people at a table, a seating area, a work spot), not the whole room or the whole terrace. That is why the key input is the usable area in m²—the area where people actually sit or stand.
For outdoor use, this guide uses a conservative minimum that works in real life (wind, imperfect mounting, and edge zones): 200 W per m² of usable area. With this rule, 6 m² always means at least 1200 W. The goal is to avoid the common “on paper it should be enough, but it feels weak” problem.
Step 1: Measure the usable area (not the total area)
Measure the area you want to feel warm as a simple rectangle:
Usable area (m²) = length (m) × width (m)
Examples:
- Seating group: 2.0 m × 3.0 m = 6 m²
- Table zone: 2.5 m × 2.5 m = 6.25 m²
- Long bench zone: 1.5 m × 4.0 m = 6 m²
If the area is not a perfect rectangle, estimate it as one. For sizing, a clear, practical estimate is better than an “exact” number that does not match real use.
Step 2: Calculate the required power (outdoor zone heating)
Outdoor zone heating: minimum 200 W/m²
Formula:
Total power (W) = usable area (m²) × 200
So you get:
- 4 m² ≙ 800 W
- 5 m² ≙ 1000 W
- 6 m² ≙ 1200 W (minimum)
- 8 m² ≙ 1600 W
- 10 m² ≙ 2000 W
- 12 m² ≙ 2400 W
Step 3: Decide how many heaters you need (comfort and even heat)
Watts answer “how much power,” but not “how evenly it feels.” One strong heater can create a hot spot in the middle and cold edges. In many cases, two smaller heaters feel better than one big heater, even if the total watts are the same.
Practical rules:
- Up to 6 m²: 1 heater can work if it hits the zone well
- 6–10 m²: often 2 heaters feel more even
- 10–12+ m² or long zones: usually 2–3 heaters along the length
This is especially important when you do not have dimming (many infrared heaters are just On/Off).
Why this minimum? Outdoors, even light air movement can reduce the heat feeling. Also, real installations are rarely perfect: mounting height, angle, and the “edges” of the zone matter. 200 W/m² is a safe starting point for outdoor comfort.
Note (simple): Indoors, you can often use less for local heating. This guide focuses on outdoor-style zone sizing because it is the most demanding use case.
Quick sizing table (area ? minimum watts ? typical split)
Usable area (m²)
4
5
6
7
8
9
10
12
15
Minimum power (W)
800
1000
1200
1400
1600
1800
2000
2400
3000
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 W
1× 1400–1500 W or 2× 700–800W
2× 800–1000 W
2× 900 W oder 2× 1000 W
2× 1000 W (often better than 1×2000 W)
2× 1200 W oder 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)
Usable area: 6 m²
Minimum power: 6 × 200 = 1200 W
Option A (one heater): 1× 1200–1500 W
Works if the zone is compact and the heater is aimed so people are inside the main heat beam.
Option B (more even heat, no dimming needed): 2× 600–800 W
Often better if you want both sides of the seating area to feel similar. Also, in mild weather you can switch on only one heater.
Heater “types” (only how they affect sizing)
You do not need deep technical details. This only helps you choose how much reserve and how many units you need.
- Short-wave (often bright / “low glare”): feels more direct outdoors, often better with light wind. If aimed correctly, the minimum sizing often works well.
- “Dark” / medium-wave: pleasant in sheltered areas. In more open areas, it often needs more distribution (two units) for good comfort.
- Long-wave / panel-like: usually not the first choice for open outdoor areas. More suitable for indoor, steady heating.
Important: The sizing rule (area × 200 W/m² outdoors) stays the same. The heater type mainly affects whether you should choose one stronger unit or two smaller units.
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.
FAQ (only sizing questions)
How many watts per m² do I need?
For outdoor zone heating, use minimum 200 W/m² of usable area in this guide.
Why do you size by usable area, not total terrace area?
Because infrared heaters warm people in a zone. Total area often includes space nobody uses, which leads to wrong sizing.
Is 1200 W enough for 6 m²?
It is the minimum here. If edges feel cool, the next step is often a second heater (2×600–800 W), not just a bigger single unit.
How much area does 2000 W cover?
With the minimum rule: 2000 W ˜ 10 m² usable area outdoors.
What is better: 1×2000 W or 2×1000 W?
In many cases 2×1000 W feels more even and gives simple control (one or both), especially without dimming.
How do I size a long table row?
Keep the same watts rule (area × 200 W/m²), but distribute the power along the length with 2–3 heaters so the ends are not cold.
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