“How many heaters” rarely has a single answer because a terrace is almost never one zone. The pro approach is to size by genuinely occupied zones, then validate the geometry (height/angle/distance), wind exposure and the level of enclosure.
1) Rule #1: size zones, not square metres
“Table” zone
Seated, static: needs consistent, even comfort.
“Lounge” zone
Larger area, varied posture: prioritise wide, gentle coverage.
“Walkway / waiting” zone
Short stay: a small top-up is enough—don’t oversize it.
Goal: focus heat on people and surfaces within the useful zone. Heating “all the air” on an open terrace is inefficient.
2) The pro method in 5 steps (simple & repeatable)
- Draw occupied zones (tables, lounge, bar) and note dimensions.
- Validate mounting constraints: available height, structure (wall/ceiling), obstacles.
- Classify exposure: open / under pergola / partly enclosed / enclosed (veranda-like).
- Choose a coverage strategy: multiple aimed points vs one very powerful unit.
- Add a “reality” buffer: prevailing wind, large voids, table rotation, peak occupancy.
3) Why “one big heater” is often a mistake
Radiant density issue
One unit often pushes you to mount higher or spread wider. Result: radiant density drops and warmth feels weaker.
Comfort issue
Too hot directly underneath, too cool on the sides. Multiple well-aimed points deliver more even comfort.
Pro principle: better 2 to 4 points correctly placed than one “very strong” point in the wrong spot.
4) Quick guide: which terrace profile means more (or fewer) units?
| Configuration | Impact on quantity | What works best |
|---|---|---|
| Very open & windy | ↑ (more points, more targeted) | Strict zoning, closer mounting, precise aiming |
| Under pergola / canopy | ↔ (more stable sizing) | Even coverage, regular distribution |
| Partly enclosed (screens/panels) | ↓ (lower losses) | Fewer units, ideally zone-controllable |
| Enclosed (veranda-like) | ↓ (near-indoor logic) | Soft distribution + control to avoid overheating |
5) Real examples (logic, not “magic”)
- Zones: 2 tables (2 separate occupied zones)
- Strategy: 1 point per table, or 2 points covering both depending on layout
- Goal: heat seating, not circulation paths
Under a pergola, geometry is stable: comfort is predictable with clean distribution.
- Zone: sofa + armchairs (wide occupied zone)
- Strategy: multiple aimed points to avoid a central “hot spot”
- Goal: soft, distributed comfort for varied positions
The wider the open-air zone, the more you should multiply points instead of pushing one unit.
- Zones: table rows + waiting areas
- Strategy: zoning by “rows” + zone control
- Goal: power only occupied areas and handle peak times
Zone control isn’t a “nice to have”: it often enables correct sizing without overspend.
6) Final checklist (anti-mistakes)
Geometry & mounting
- Realistic mounting height (not “higher to cover more”)
- Aim into the occupied zone (seating)
- Obstacles: beams, lights, awnings
- Safety clearances respected
Context & use
- Prevailing wind / airflow corridors
- Enclosure level (screens/panels)
- Real occupancy (peak periods)
- Need for zoning/control (pro)
7) FAQ
Outdoors, per-m² rules are too rough. Size occupied zones and optimise height + angle + distribution.
Too many: hot spots, glare, constant need to turn down. Too few: diffuse warmth, weak sensation. Check geometry first, then zone distribution.
Because occupancy varies. Zoning powers only what’s needed and avoids oversizing.