Three parameters decide: ceiling height, envelope insulation, operating hours per year. Together they tell you whether radiant gas will save you money over convection, or not. Below is the decision tree with real numbers from installations in Slovenian and French industrial sites.
The 5-metre threshold changes everything
A hall 4 metres tall behaves differently from one 8 metres tall. Warm air rises. In a 4 m hall, convection (unit heaters that heat the air) works because the warm layer cycles back down to the work zone fast. In an 8 m hall, that warm layer gets trapped under the ceiling and leaks through poorly insulated roofs.
The concrete consequence: an 8 m hall with gas unit heaters typically burns 25 to 30 percent more gas than the same 8 m hall with radiant plaque heaters. The reason is not output. The reason is heat-transfer direction. Radiation heats objects and people directly, not air. The air in the hall does not get stuck under the ceiling because we never heated it.
This rule holds from roughly 5 metres up. Below 5 m the difference is smaller, though still usually favouring radiation. Above 8 m the difference is dramatic.
The three parameters that answer the question
Before picking technology, measure or estimate three things about the building:
| Parameter | Range | Effect on choice |
|---|---|---|
| Ceiling height | 4 to 12 m + | Below 5 m: unit heater or radiant. Above 5 m: radiant strongly preferred. Above 8 m: radiant almost mandatory. |
| Envelope insulation | Old hall no insulation, average, modern | Poor insulation amplifies the radiant advantage. Good insulation narrows the gap (unit heaters become competitive). |
| Operating hours per year | 800 (seasonal, single shift) to 6000+ (24/7 production) | Over 3000 hours warrants condensing technology (investment recovered in 2 to 4 years). |
Without these three numbers, any further technology conversation is approximate guessing. With them, the choice is obvious in 80 percent of cases.
Four technologies, four use cases
Solaronics divides the catalogue into four families. Each solves a different problem.
Radiant plaque heaters (infrared)
Models: SRII, Encased SRII, SolarHP. A gas burner heats a ceramic plate to 900 °C. The plate emits infrared directly onto objects, people, and floors below. The air does not get heated directly.
Typical output: 6.2 to 25.7 kW per plate. Mounting height range: 4 to 15 m.
Real case: Aéroport de Genève hangar, 24 SRII 81 plates (25.7 kW each), 7 m mount height, G20 gas. Annual saving versus the previous convection system: 32 percent on the gas bill.
Gas unit heaters
Models: Minigaz, AC condensing. A gas burner heats air through a heat exchanger; a fan pushes warm air into the hall. Classic convection.
Typical output: 20 to 100 kW per unit. Mounting height optimum: 3 to 6 m.
Real case: cold-chain warehouse in Maribor, 4 AC 45-H condensing units, 105 percent seasonal efficiency, G31 (propane). Insulation here pays off: investment recovered in 2.8 years.
When should you pick unit heaters over radiant? When the hall is well insulated, below 5 m, and operating hours are high (condensation pays the investment back fast).
Air curtains
Models: MRA, MRA-H. Warm-air curtain over an entrance. Stops cold air entering when doors open (logistics, loading docks).
Typical output: 14 to 44 kW. Doors up to 4 m wide.
Real case: Hofer Slovenija loading dock, MRA 45-H over double sectional doors, 60-second opening cycle. Indoor-heating saving: 40 percent, because air does not escape.
Warm-air generators
Models for temporary buildings, construction sites, halls with seasonal use. Mobile or semi-mobile setup. Fast response.
Typical output: 30 to 150 kW. Lower efficiency than stationary systems, but flexibility wins.
When? When the hall is not permanent. When flexibility outweighs efficiency.
Three most common mistakes
After ten years of sizing on the Slovenian and Adriatic market, three patterns recur.
Mistake 1: choosing by burner price, not system efficiency. A cheaper condensing unit heater without modulation burns more gas in practice than a more expensive condensing unit with 30-100 percent modulation. Investment difference: 8 percent. Annual gas-bill difference: 12 to 18 percent. The premium pays back in less than two seasons.
Mistake 2: ignoring the operating regime. A hall running 6:00 to 14:00 has a different control curve from a hall running 24/7. Buyers often assume "heating is heating". Result: oversized morning-warmup capacity (unnecessary investment) or undersized steady-state capacity (failing to reach working temperature).
Mistake 3: no zoning. A large hall (over 1000 m²) with one zone heats production and storage the same way. Storage does not need 18 °C; production does. Proper zone-by-zone control saves 15 to 25 percent of the gas bill through programming alone.
Decision tree
If you have a hall under 5 m, well insulated, with 1500 operating hours, a condensing unit heater is probably right.
If you have a 5 to 8 m hall with mixed production and storage, the combination of radiant over work zones plus unit heaters over common areas gives the best system efficiency.
For a hall over 8 m with an uninsulated roof and long operating hours, radiant plaque heaters are almost always the right choice.
If you have tall entrance openings (logistics, loading docks), an air curtain is an add-on to the main system, not a replacement.
How we verify real numbers
Every concrete inquiry reaches a technical engineer, not a marketing department. We send you:
- A specific model recommendation from the catalogue, sized to your project parameters.
- An investment estimate and a saving estimate against your current system.
- A payback timeline for your specific operating curve.
- The datasheet, dimensional drawings, and warranty terms.
Response within 24 business hours. All numbers from our own installations over the last ten years, not from the manufacturer's brochures.
Related: Radiant vs unit heaters, Heating power calculation, ErP seasonal efficiency.