Radiant plaque heaters vs. gas unit heaters: when to pick which
Radiant heats objects and people directly via infrared; a unit heater heats air (convective heating). A unit heater heats air through a heat exchanger and pushes it into the hall. The physics difference becomes a gas-bill difference. Below: the decision table, three real installations, and three cases where the unit heater is still the right pick.
Quick reference: when which
| Condition | Radiant wins | Unit heater wins |
|---|---|---|
| Ceiling height | over 5 m | under 5 m |
| Envelope insulation | poor to average | good (modern build) |
| Operating hours | long (>3000 h/year) | short or seasonal |
| Work pattern | local workstations, assembly | uniform heated zone |
| Air movement tolerance | must be minimal (welding, dust) | acceptable |
| Entrance openings | rare | frequent, small |
| Investment | higher | lower |
| Annual gas bill | 25 to 30 % lower | higher |
In 80 percent of cases the table answers itself. The remaining 20 percent are edge cases where sizing needs a specific calculation.
The physics in two sentences
Radiant (infrared): a gas burner heats a ceramic plate to 900 °C; the plate emits infrared down. The hall air does not get heated directly; objects that absorb the infrared do. People in the work zone reach working temperature without us heating the full volume above them.
Unit heater (convection): a gas burner heats air through a heat exchanger; a fan pushes the warm air into the hall. Hot air rises, cools, cycles back down. The whole hall warms uniformly, including the volume above the work zone.
What this means in practice: in an 8 m hall, radiant heats 4 m of volume in the work zone. The unit heater heats all 8 m of volume. Warm air above 4 m does nothing useful until it cools back to 18 °C at work-zone level. In a poorly insulated building that air cools through the roof before it cycles back, so the unit heater burns extra gas to reheat.
Three real installations
Case 1: 9 m production hall, poor insulation, radiant wins
Automotive components factory, 9 m tall, ceiling insulation from the 1980s, four work zones. Before: six gas unit heaters, annual gas bill 18 000 EUR over 2200 operating hours.
Replacement: twelve SRII radiant plaque heaters, 8.5 kW each, mounted at 7 m, G20 gas. Investment 32 000 EUR.
Annual bill after: 12 200 EUR. Saving 5 800 EUR/year. Payback: 5.5 years.
Why it worked: the old insulation made unit heaters inefficient. Radiant bypassed the whole-volume heating problem.
Case 2: 4.5 m modern warehouse, good insulation, unit heater wins
Cold-chain logistics centre, 4.5 m tall, PIR insulation 12 cm, dual-zone distributor. Before: eight old radiant plaque heaters from the 1990s, annual gas bill 14 000 EUR.
Replacement: four Solaronics AC 45-H condensing unit heaters, 45 kW each, G31 (propane). Seasonal efficiency 105 percent. Investment 28 000 EUR.
Annual bill after: 8 400 EUR. Saving 5 600 EUR/year. Payback: 5 years.
Why it worked: good insulation means a unit heater retains heated air instead of losing it. Condensation saves an additional 15 percent of gas by recovering latent heat from flue-gas water vapour.
Case 3: 6 m showroom + 4 m workshop, hybrid wins
Car dealership with showroom (6 m) and workshop (4 m). Different temperature profiles: showroom 22 °C all day, workshop 16 °C only during work hours.
Solution: SRII radiant plate 12.8 kW over showroom (local heat without draught) plus Minigaz condensing unit heater 30 kW in the workshop (uniform heating). Total investment 18 000 EUR.
Annual bill: 9 600 EUR over 2400 operating hours. A uniform radiant-only system would have crossed 13 000 EUR (heating the workshop volume completely), a uniform unit-heater system would have crossed 14 500 EUR (showroom draught loss).
Investment comparison
| System | Investment EUR / 1000 m² | Annual gas EUR / 1000 m² | Payback |
|---|---|---|---|
| Old unit heater (>15 years, inefficient) | 0 (existing) | 20 000 - 28 000 | n/a |
| Classic new unit heater | 18 000 - 25 000 | 14 000 - 18 000 | 4-7 years depending on hours |
| Condensing unit heater | 28 000 - 38 000 | 10 000 - 13 000 | 5-8 years |
| SRII radiant plaque heaters | 28 000 - 42 000 | 9 000 - 12 000 | 4-7 years |
| Radiant + condensing hybrid | 40 000 - 55 000 | 8 000 - 11 000 | 6-9 years |
Numbers from eight installations in the Slovenian industrial sector, 2019 to 2025. Gas prices normalised to 2024 average (EUR/MWh).
Three common myths
Myth 1: "Radiant only heats directly under the plate." The plate emits infrared in a cone with full angle 60 to 90 degrees. At 7 m mount height, the heated floor zone is a square 8 to 12 m on a side. Plate layout achieves homogeneous work-zone heating.
Myth 2: "Unit heaters are always cheaper for seasonal use." For seasonal use under 1500 hours/year the unit heater is cheaper to install. But seasonal use is usually paired with heavy building insulation (modern build). In old buildings with long operating seasons, radiant is cheaper after two years.
Myth 3: "Radiant dries out the air." Radiant does not heat air, so it does not change humidity directly. The "dry air" feeling in radiant-heated halls comes from dust that convection does not displace (a unit heater's air movement partially clears it). That is a work-comfort issue, not a technical property of radiant.
Four-step decision path
- Measure ceiling height. Under 5 m: consider a condensing unit heater. Over 5 m: consider radiant.
- Assess insulation. Poor: strongly prefer radiant. Good: the gap between technologies narrows.
- Count operating hours. Under 1500: condensing or radiant investments don't pay back. Over 3000: both pay back.
- Identify mixed-regime zones. Multiple zones with different profiles: consider a hybrid (radiant + condensing).
Four steps make the decision. After step four, send us the parameters; we return a specific model proposal within 24 hours.
Related: Radiant heaters and unit heaters in the catalogue, power sizing, stratification.