A greenhouse can have liquid propane left in its tank and still lack the vapor supply needed by its heaters. Remaining fuel inventory answers how much energy is stored. It does not, by itself, establish the rate at which a vapor-withdrawal system can supply that energy on a cold night.
Before accepting a heating proposal, ask the qualified fuel-supply provider to review the lowest planned temperature and minimum operating fill together with the sustained simultaneous appliance demand. Treat that review as a documented condition of the purchase.
Keep two fuel questions on separate lines
The inventory question concerns usable fuel stock, expected consumption and refill access. The delivery question concerns the fuel rate available to the appliances under the stated operating conditions. A calculation of “days remaining” can address the first question while leaving the second unanswered.
The RegO LP-Gas Serviceman's Manual explains that vapor withdrawal draws on heat transfer into the liquid. For the described aboveground natural-vaporization arrangement, colder conditions and less liquid-covered vessel surface can reduce vaporizing capacity. Its load review uses appliance fuel-input ratings. The manual is a professional reference; its installation tables and cited code editions are not a current site approval.
Fuel input and useful heat output are different ratings. Send the provider the manufacturer's fuel-input information for each appliance, along with the approved operating sequence. Do not substitute a boiler's useful output rating or a seasonal fuel bill.
Define the cold case before discussing a container
The National Greenhouse Manufacturers Association's heating guidance identifies the commercial problem directly: cold-night greenhouse demand can coincide with reduced propane vaporization. This is historical industry guidance, useful for framing the question, not for approving a current installation.
Give the fuel specialist the project's minimum design ambient condition and the planned minimum fill. Ask which liquid-temperature assumption their capacity evidence uses and how the duration of the draw is represented. “Winter service” is not a defined capacity case.
Identify the actual fuel specification. A propane capacity table cannot automatically represent an unspecified propane/butane mixture. Likewise, aboveground and buried arrangements need their own documented basis. Do not transfer a figure between containers merely because their nominal stored volume is similar.
The greenhouse team can collect these records without manipulating the gas system. Container identity and configuration should come from supplier documentation, accessible approved records or a qualified inspection. Missing information stays missing until the responsible provider resolves it.
Account for the permitted simultaneous demand
List every appliance connected to the reviewed supply, including any approved equipment outside the greenhouse that shares it. Record the maximum fuel input from its nameplate or current manufacturer document, the number installed and the proposed simultaneous operating state.
If the proposal assumes that some appliances cannot run together, attach the designer-approved basis. An operator's expectation that one heater will probably remain off is not an established demand limit. Conversely, do not invent an operating sequence to reduce the total on paper.
Keep draw duration visible. A brief startup observation does not document capacity during a sustained cold period. The provider should state the conditions and period for which its capacity assessment applies, including the defined backup case.
Send a three-case evidence sheet to the provider
Use the same appliance list and units across the cases. Record inventory/autonomy separately from delivery capacity even when both are expressed in energy-related units. Attach documents rather than filling gaps with generic internet tank tables.
| Record or decision | Warm/full reference case | Cold/low-fill or backup case |
|---|---|---|
| Case ID, purpose and sustained draw duration | ________ | ________ |
| Fuel specification and supplier document | ________ | ________ |
| Approved container identity and aboveground/buried arrangement | ________ | ________ |
| Design ambient and documented liquid-temperature assumption | ________ | ________ |
| Planned fill state and inventory unit | ________ | ________ |
| Inventory/autonomy evidence, consumption basis and refill access | ________ | ________ |
| Appliance list, fuel-input ratings and source documents | ________ | ________ |
| Permitted simultaneous demand, units and sequence approval | ________ | ________ |
| Provider vapor-capacity evidence for this exact state | ________ | ________ |
| Supported sustained supply rate and applicable conditions | ________ | ________ |
| Regulator/piping delivery confirmation from fuel specialist | ________ | ________ |
| Supported / mismatch / unresolved capacity flag | ________ | ________ |
| Required supplier resolution, reviewer and date | ________ | ________ |
Complete an additional limiting-case sheet for the defined backup arrangement; do not merge two different assumptions into one column. A backup appliance connected to the same reviewed supply must be included in the relevant demand case.
Require the whole delivery path to be supported
A favorable container-capacity statement leaves an open question if the provider has not confirmed delivery through the specified regulator and piping. Ask for one coordinated conclusion that identifies the reviewed equipment, conditions and unresolved items.
This is not an invitation to select pipe sizes or alter pressure. It is a request for the responsible fuel professional to show that the complete proposed arrangement supports the appliance requirements. The greenhouse buyer should be able to trace that conclusion to the drawings and order documents.
When evidence is incomplete or shows a mismatch, hold the supply-capacity decision and return it to the provider. The provider must propose and approve the appropriate solution under the applicable local requirements. This article cannot recommend a tank size or certify fuel-system compliance.
Do not turn the review into a field experiment
Do not heat, wrap, pour water over or otherwise modify a tank to complete this assessment. Do not adjust regulators, change manifolds or connections, purge equipment or run a live fuel-exhaustion test. A visible condition such as frosting does not establish a single cause or authorize an intervention.
The useful outcome is a supplier-supported cold/low-fill capacity decision, retained with the heating purchase. Fuel stock and refill planning remain necessary, but a full inventory record should never be mistaken for evidence of the required hourly delivery.
Download the working files
Use these CSV files with the instructions in this article.