Size bulk LPG storage tanks and cylinder banks from your connected gas load — get peak demand, daily consumption, required storage capacity, recommended standard tank size and a natural vaporization check. Based on NFPA 58 practice.
How to Size an LPG Storage Tank
LPG (Liquefied Petroleum Gas) storage sizing balances three things: the peak vapor demand of the connected appliances, the consumption between refills, and the tank's ability to naturally vaporize liquid LPG fast enough to feed that demand. Undersize the tank and you'll run out of gas or starve appliances in cold weather; oversize it and you pay for capacity, civil works and safety distances you don't need.
Step-by-Step Method Used by This Calculator
- Total connected load — add the nameplate gas input of every appliance (burners, ovens, fryers, boilers, water heaters). Enter it in kg/hr, kW, BTU/hr or MJ/hr.
- Apply diversity — appliances rarely all fire at once. Commercial kitchens typically use 60–80%; continuous process loads use 100%.
- Daily consumption — peak demand × equivalent full-load operating hours per day.
- Storage autonomy — multiply by the days you want between tanker refills (7–15 days is common practice; check supplier delivery frequency in your area).
- Convert to tank water capacity — LPG is stored as liquid at roughly 0.51 kg/L (propane) to 0.575 kg/L (butane), and tanks may only be filled to about 85% of water capacity per NFPA 58.
- Vaporization check — the tank must supply vapor at the peak rate using only ambient heat through its wetted shell; otherwise a forced vaporizer is required.
LPG Tank Sizing Formulas
Peak Demand (kg/hr) = Connected Load × Diversity Factor
Daily Use (kg/day) = Peak Demand × Operating Hours
Storage (kg) = Daily Use × Autonomy Days
Tank Water Capacity (L) = Storage ÷ (LPG density × Max Fill %)
Energy conversion: 1 kg of LPG ≈ 12.7–12.9 kWh ≈ 46 MJ ≈ 43,700–44,000 BTU. So a 100 kW connected load draws roughly 7.8 kg/hr of LPG at full fire.
Worked Example: Hotel Kitchen
A hotel kitchen with 350 kW total connected gas load, 70% diversity, 8 equivalent full-load hours/day and 10-day autonomy using LPG mix:
- Peak demand = 350 ÷ 12.8 × 0.70 ≈ 19.1 kg/hr
- Daily consumption = 19.1 × 8 ≈ 153 kg/day
- Storage = 153 × 10 = 1,530 kg → water capacity = 1,530 ÷ (0.54 × 0.85) ≈ 3,335 L → select a 5,000 L bulk tank
- A 5,000 L tank in a 10 °C minimum-ambient climate naturally vaporizes well above 19 kg/hr — no vaporizer needed.
Design & Safety Notes
- Fill limit: LPG liquid expands with temperature — tanks are filled to a maximum of ~85% water capacity so the relief valve never sees liquid (NFPA 58).
- Butane in winter: butane boils at ~0 °C, so butane-rich LPG will not vaporize naturally in cold climates — use propane or a vaporizer.
- Safety distances: NFPA 58 and local civil-defense rules dictate minimum separation from buildings, boundaries, ignition sources and openings based on tank capacity — verify with your local authority before finalizing location.
- Redundancy: for critical loads, consider 2 smaller tanks instead of 1 large tank, or a cylinder-bank standby.
- Vaporization margin: the vaporization figure in this tool is an indicative estimate (horizontal bullet tank, ~30% fill worst case, still air). Always confirm against the tank manufacturer's vaporization tables.
Frequently Asked Questions
How do I calculate LPG tank size?
Peak demand (kg/hr) × daily hours × storage days = storage in kg. Divide by LPG density (≈0.51–0.575 kg/L) and the 85% max fill to get tank water capacity in litres, then pick the next standard tank size.
Why only 85% fill?
Liquid LPG expands with temperature. The ~15% vapor space prevents hydraulic filling and relief-valve lift on hot days — a code requirement under NFPA 58.
What diversity factor should I use?
Commercial kitchens: 60–80%. Small multi-appliance installations: 70–80%. Continuous industrial/process burners: 100%. When unsure, size conservatively at the higher factor.
When do I need an LPG vaporizer?
When peak vapor demand exceeds the tank's natural vaporization — typical with large loads on small tanks, cold climates, or butane-rich LPG. The tool flags this automatically and a forced vaporizer (electric or hot water) solves it.
Bulk tank ya cylinder bank — which one?
Below roughly 500–1,000 kg storage, a manifolded 47.5 kg cylinder bank (duty + standby with auto changeover) is usually cheaper and easier to permit. Above that, bulk tanks refilled by tanker are more economical.
Disclaimer: Results are for preliminary engineering estimation only. Final tank selection, siting and safety distances must comply with NFPA 58, the tank manufacturer's data and local authority / civil defense regulations.