“How many heaters do I need?” is the question we answer most. The honest reply: it depends on three things you can measure in ten minutes — the size of the zone you actually sit in, how exposed it is, and what you can mount to. Here's the method we use when we size systems for customers.
Prefer to skip the math? Send us your patio dimensions and a photo via the contact page and we'll size it for you — free.
Step 1: Size the zone, not the patio
Radiant heaters warm people, not property lines. Measure the area where people actually sit — the dining table plus chairs, the lounge corner — not the full slab. A 400 sq ft patio with a 10×12 ft dining zone needs a heater sized for 120 sq ft, positioned over that zone. This is the single most common oversizing mistake.
Step 2: Classify your exposure
- Enclosed / mostly enclosed: solid roof, two or more walls or screens. Heat lingers; you need the least wattage.
- Covered but open: solid roof or pergola, open sides. The standard case — radiant heat works well, breezes steal some of it.
- Fully exposed: no roof, open to wind. Expect to need roughly half again to double the wattage of a covered space — and consider gas instead (more on that below).
Step 3: Match wattage to zone and exposure
These planning ranges assume typical cool-evening use (roughly 45–60°F outdoor temperatures) and correct mounting height. Treat them as a starting point, not physics — wind and mounting height move the numbers substantially:
| Seating zone | Enclosed | Covered, open sides | Fully exposed |
|---|---|---|---|
| Small (up to ~60 sq ft) — bistro table, 2–4 people | 2,000W | 2,000–3,000W | 3,000–4,000W |
| Medium (~60–120 sq ft) — dining table for 6 | 2,300–3,400W | 3,000–4,500W | 4,500–6,000W or gas |
| Large (~120–200 sq ft) — dining + lounge | 2 × 2,300–3,000W | 2 × 3,000–4,000W | 2+ × gas units |
Notice the pattern in the last row: past ~120 sq ft, add heaters instead of watts. Two mid-wattage units at the edges of a zone produce far more even warmth than one monster unit in the center, because radiant intensity falls off quickly with distance.
Step 4: Check mounting height against the spec sheet
Wattage and mounting height are one decision, not two. A 3,400W heater mounted at 7.5 ft warms a dining table beautifully; the same unit at 10 ft warms nobody. Every heater we sell lists the manufacturer's height window and clearance diagram on the product page — check it against your ceiling or pergola before you commit to a wattage. If your structure is tall (10 ft+), that usually pushes you to the next wattage class or to gas.
When the answer is gas
We size a lot of systems, and for fully exposed, breezy terraces we usually recommend a Tungsten Smart-Heat Gas rather than stacking electric wattage: gas radiant units simply throw more heat into moving air, and a freestanding portable propane unit needs no structure at all. Electric wins under cover — see our complete electric buying guide for that side of the decision.
The mistakes we see most
- Sizing for the whole patio instead of the seating zone — leads to overspending on wattage that warms empty concrete.
- One big heater in the middle of a long space — the ends stay cold. Distribute smaller units.
- Ignoring the electrical plan. Hardwired heaters need dedicated 240V circuits; a 2 × 4,500W setup is a 37A load. Loop in your electrician before ordering, not after.
- Skipping the dimmer. Right-sized for the coldest evening means oversized for most evenings — variable control fixes that.
Get it right the first time: browse the patio heater collection, or send us your dimensions for free sizing help and a formal quote.