Stratification is not a failure, it is physics. With convective heating, columns of warm air rise to the ceiling, where the densest layer of heated air accumulates while a worker below is heated to 16 °C. The thermostat (typically at 1.8 m height) reads 16 °C and calls for more heat. With a 9 m ceiling, the roof can reach 28 °C before the thermostat hits the 18 °C setpoint. The 12 K differential × volume above the working zone = energy loss.
Typical gradient
A measurement from a real installed hall (sandwich panel, 8 m ceiling, 2× gas unit heater 80 kW):
| Height | Measured temperature |
|---|---|
| 0.1 m (floor) | 14.2 °C |
| 1.8 m (worker, thermostat) | 18.0 °C |
| 4.0 m (middle) | 22.8 °C |
| 7.5 m (under ceiling) | 26.4 °C |
Gradient: 1.5 K/m. The ceiling is heated 8.4 K above target. Across an 800 m² ceiling, 8.4 K of excess loss ≈ 16.8 kW of constant heat waste.
Three solutions, in order of preference
1. Radiant heating instead of unit heaters. Infrared radiation heats surfaces (floor, workbenches, people), not air. A gas radiant plaque at 8 m height heats the floor to 18 °C and the ceiling to 19–20 °C. The gradient practically vanishes. This is a structural fix, it prevents the problem, doesn't patch it.
2. Destratifier (air mixer). A ceiling-mounted axial fan that pushes warm air back to the floor (Solaronics CA destratifier or DR ceiling fan). Electric (~150–400 W), mounted on the roof structure. Reduces the gradient to 0.3–0.5 K/m. Effective for retrofitting convective systems, an added investment to an existing installation. Cost per unit: €350–800, one destratifier per ~200 m² of floor area.
3. Roof insulation + lower setpoint. In older halls with uninsulated roofs, the ceiling not only stores warmth but radiates loss to the outdoors. Adding 60–80 mm PUR insulation cuts total heat loss by 15–25 %, indirectly reducing stratification (less total heating required).
When to apply which
| Hall condition | Recommendation |
|---|---|
| New project, ceiling above 5 m | Radiant heating (prevention) |
| Existing unit heater, ceiling 5–8 m | Destratifier (retrofit fix) |
| Existing unit heater, ceiling above 8 m | Hybrid: unit heater + destratifier, with a planned migration to radiant over the medium term |
| Uninsulated roof, any regime | Insulate before heating (the investment pays back every year) |
Decision check
Measure the gradient (thermometer at 1.8 m vs 0.1 m) on two days: a cold one (outdoor < 0 °C) and a mild one (5–10 °C outdoor). If the cold-day gradient is > 1.2 K/m and the average ceiling height is ≥ 6 m, a destratifier or technology change is economically justified within 3–5 years.
Destratifier noise and mounting specifications
Practical numbers a vendor rarely highlights in the brochure:
- Noise at operating speed: 38–48 dB(A) measured 3 m below the fan. For static work (packing, QC) pick a quieter variant (under 42 dB). In a warehouse up to 55 dB is fine.
- Mounting clearance: minimum 0.4 m below the ceiling for airflow above the blades. At very low ceilings (5.5 m) the return flow is ineffective, alternative is radiant.
- Controller coupling: activation by temperature gradient (detects floor-to-ceiling diff > 3 K), not a timed cycle. Without gradient sensing the destratifier runs even when no stratification exists and only adds electricity cost.
- Electrical consumption: 150–400 W per unit. Annual 700–1 600 kWh at 4 000 hours of operation, cost €130–290. Against 8–12 % heat savings (≈ €800–1 500/year for a 1 500 m² hall) payback is < 12 months.