When a greenhouse replaces natural-gas heating, its CO₂ budget may need rebuilding as well. If the existing plant provides both heat and enrichment gas, a cheaper heating proposal can still leave a missing service. Price and secure that service before crediting the full heating saving.
The useful comparison is the cost of running the same crop with the existing combined arrangement versus the proposed heating system plus its separately supplied CO₂. This makes the transition easier to judge and exposes dependencies that a heat-only quotation can miss.
One sector, two very different area averages
The WUR Energy Monitor of Dutch greenhouse horticulture 2024, section 3.4, published in October 2025, estimated external CO₂ purchases at 0.73 million tonnes in 2024, up 12% from 2023. Its provisional Netherlands-wide figures use two area bases:
| Published average | Area included in the denominator |
|---|---|
| Slightly above 7 kg/m² | All greenhouse area in the sector |
| 20–30 kg/m² | Greenhouse area actually using external CO₂ |
These monitoring estimates combine sector and supplier information; they are not crop trials or dosing recommendations. Using the all-area average for a farm that buys external gas could badly misrepresent its budget. Neither row establishes what a particular supplier can deliver to that farm.
Recover the service hidden in the old energy bill
Start with records of how the current greenhouse obtains enrichment gas during each crop period. Separate purchases from gas supplied through the existing heating arrangement. Then identify which contribution disappears, which remains and which changes when the new heat source is introduced.
This avoids two common budgeting errors. The first is to assume that enrichment remains available without assigning it any cost. The second is to assign the full old fuel bill to both heating and CO₂, then claim to save it twice. Keep one total cost for the existing package and explain any allocation used for comparison.
A seasonal plan is more useful than one annual number. A supplier may discuss sufficient annual tonnage while offering different delivery conditions during the crop periods when the greenhouse needs it. Ask the crop adviser to define the demand profile from the actual crop plan, then ask suppliers to confirm the corresponding service.
Put these six lines into the transition budget
- Crop basis. Record the growing area, production months and expected accepted output shared by both options. Explain any change rather than hiding it inside the energy saving.
- Replacement heat. Include the proposed heating service, operating cost and any fixed or connection charges attributable to the change.
- External CO₂ quantity. Use a documented mass by crop period. Keep tonnes and kilograms consistent with the supplier’s price unit.
- Delivered price. Confirm whether the quotation includes transport and other delivery charges. Add minimum purchases or fixed fees only once.
- Availability commitment. Record the confirmed supply window, quantity limitations, notice requirements and which party carries interruption risk.
- Fallback consequence. Identify the cost of an available alternative or the crop-performance exposure if the planned supply is interrupted. An unconfirmed alternative belongs in a risk case.
The basic purchase arithmetic is documented tonnes multiplied by the matching delivered price per tonne, plus charges not already included. It remains incomplete until the timing and contractual terms match the crop requirement. A low unit price with an unsuitable minimum purchase can be expensive for a seasonal user.
Compare complete packages before committing
Build a base case using the service the suppliers will actually stand behind. Then test what happens if external CO₂ costs more, arrives less reliably or requires additional fixed expenditure. Keep any assumed crop response visible alongside the cost change; maintaining the same yield is itself an assumption if the enrichment service changes.
The decision to proceed becomes stronger when the heat saving remains worthwhile after the full CO₂ arrangement is included and the seasonal supply is credible. If the case works only with an unsigned supply assumption, settle that dependency before removing the existing service.
For the surrounding heating and electrical demand, use the greenhouse energy-demand guide. The immediate task here is a complete operating comparison that the grower, heating supplier and CO₂ supplier can all recognize.