Heating and emitters in commercial buildings: radiators, underfloor heating, fan coil units
Regulatory framework: a 40% reduction expected by 2030
Heating accounts for 40 to 50% of the kWh consumed in an office building: it is the ONLY area that makes the -40% target by 2030 mathematically achievable. Optimising lighting or office equipment will never be enough to stay on the regulatory trajectory applicable to commercial buildings. Kytom sizes low-temperature radiators, underfloor heating, fan coil units and radiant panels according to the prevailing methodology for calculating heat losses, with target outputs of 60 to 100 W/m² and setpoints fixed at 19 °C during occupancy, controlled via BACnet or Modbus BMS. Heating in commercial offices is no longer just a boiler and a few emitters: performance is calculated, controlled and reported. Three constraints shape every project: the regulatory trajectory for reducing consumption, RE2020 for new builds, and perceived comfort measured post-occupancy. Projects delivered since 2006 document significant reductions in heating consumption from the very first year, with a 12-week integration timeline including technical works packages.
The French tertiary decree imposes a trajectory for reducing energy consumption in buildings larger than 1,000 m²: -40% in final energy consumption by 2030, -50% by 2040, -60% by 2050, compared with a reference year after 2010 (decree no. 2019-771, art. R. 174-22 et seq. of the French Construction Code). Heating concentrates 40 to 50% of the kWh consumed, making it the main source of savings in French commercial offices.
The technical requirements are cumulative:
- NF EN 12831-1:2017: calculation of heat losses by zone.
- NF EN 442-2: thermal performance of radiators.
- DTU 65.14: installation of hydronic underfloor heating.
- Regulatory carbon content of electricity for heating: 79 gCO2/kWh, compared with 210 gCO2/kWh in the earlier E+C- framework.
- BREEAM and associated voluntary certification frameworks.
Kytom’s reading, departing from professional orthodoxy. Many project managers present this as an annual declaratory constraint. In practice, the real turning point lies elsewhere: the chosen reference year, often 2015-2019, locks the trajectory for 20 years. A poor choice of reference can make the 2030 target unattainable without major renovation, or conversely make it trivial. This strategic decision is made before any HVAC sizing, not after.
Clients supported by Kytom express three converging priorities: control of the energy budget, thermal comfort for staff across floor plates of 500 to 1,000 m², and annual reporting. The rise in energy costs over the 2021-2023 period remains a structuring factor in these decisions. Labour regulations set a general obligation to maintain a suitable temperature in premises, without a direct numerical value.
The Kytom method in 5 steps planned over 12 weeks
The method unfolds over an average of 12 weeks, HVAC works packages included.
- Thermal audit: survey of existing emitters, measurement of temperatures by zone, analysis of bills over 3 financial years, calculation of heat losses according to the reference standard method for calculating building thermal loads.
- Sizing by use: division of the floor plate into zones (open space, meeting rooms, phone booths, break areas) with target outputs adapted to the insulation level of each zone.
- Choice of emitters: low-temperature radiators 45/35 °C, hydronic underfloor heating installed according to DTU 65.14, 2- or 4-pipe fan coil units for zones with high variability, radiant panels above 4 m of ceiling height.
- BMS integration: BACnet or Modbus protocol, presence sensors, night setback to 16 °C, weekly schedule.
- Commissioning: commissioning with documented hydronic balancing, training of the facility manager, 2 to 3 days minimum.
The noise level of the fan coil units stays below 38 dB(A) in enclosed offices, in line with the reference acoustic requirements for commercial buildings, a point verified at handover. Fluid engineering firms coordinate the works packages with partner HVAC companies.
When this method is not the right one. Below 300 m² or for a residual lease of less than 4 years, the return on investment of a full HVAC overhaul with BMS is generally too slow to be justified: a simple replacement of emitters with connected thermostatic valves is enough. Likewise, for a heritage building or one with a strong ABF constraint on ceiling drops, the integration of ducted fan coil units is not relevant: opt instead for surface-mounted low-temperature radiators. Beyond a legacy 70/50 °C regime retained with a recent gas boiler less than 8 years old, a forced switch to low temperature degrades the annual efficiency without significant regulatory gain before the 2030 deadline.
Comparison of emitters: 4 technologies for 4 uses
The choice of emitter depends on the flexibility of the partitioning, the ceiling height, the available heat source and the budget. Kytom’s fluid engineering firms decide zone by zone.
| Emitter | Typical regime | Output | Inertia | Priority use |
|---|---|---|---|---|
| Low-temperature radiator | 45/35 °C | 60 to 100 W/m² | Low | Stable floor plates, heat-pump compatible |
| Hydronic underfloor heating | 35/30 °C | 50 to 80 W/m² | 3 to 6 h | Lobbies, reception areas, prestige spaces |
| 4-pipe fan coil unit | Hot/chilled water | 80 to 120 W/m² | Less than 10 min | Reconfigurable open spaces, heating/cooling |
| Radiant panel | Electric or water | 70 to 110 W/m² | Less than 5 min | Ceiling height > 4 m |
The indicative output values, from 60 to 100 W/m² for a low-temperature radiator, 50 to 80 W/m² for hydronic underfloor heating, 80 to 120 W/m² for a 4-pipe fan coil unit and 70 to 110 W/m² for a radiant panel, are consistent with manufacturers’ technical data sheets and the usual orders of magnitude in commercial building HVAC engineering.
Kytom’s position, against the « underfloor heating everywhere » trend in offices. Marketing orthodoxy positions underfloor heating as the comfort benchmark. Our reading differs for commercial offices undergoing renovation: its 3 to 6 h inertia makes it unsuitable for floor plates with intermittent occupancy, unoccupied weekends or remote-working days, where the BMS must be able to restart a zone in under 30 min. On the commercial floor plates supported in renovation projects, underfloor heating was mostly chosen for lobbies and reception areas; office floor plates favoured low-temperature radiators or fan coil units, which are more compatible with the time-based scheduling required by the tertiary decree.
Switching to a low-temperature 45/35 °C regime, a prerequisite for coupling an air/water heat pump, requires oversizing the emitters by 30 to 50% compared with a legacy 70/50 °C regime.
Frequently asked questions
What heating output should be planned for a commercial office floor plate?
Between 60 and 100 W/m² depending on the building’s insulation, with a precise zone-by-zone calculation of heat losses. A preliminary audit is essential before any sizing.
Is underfloor heating suitable for a commercial open space?
Rarely in refurbishment projects. Its 3-to-6-hour inertia makes it incompatible with fine hourly control on floors with intermittent occupancy, where the French tertiary decree mandates consumption reductions that are hard to achieve with such an unresponsive system. Underfloor heating is better suited to new builds designed around this solution from the outset.
