← Marine · Marine Electrical Systems
Add running watts of all AC loads. Add startup surge for biggest motor (typically AC). 13,500 BTU marine AC: ~1,500W running, 2,500–3,500W startup. Size generator above total. See marine electrical systems.
Boat generator sizing: AC load math, air conditioning, startup surge. NFPA 70 and ABYC govern marine generator installations. Same principles as RV generator sizing.
Add running watts: AC (1,500W) + refrigeration (200W) + battery charger (300W) + outlets (500W) = 2,500W base. AC startup surge: 2,500–3,500W. Generator must handle surge.
| Load | Running | Startup |
|---|---|---|
| 13,500 BTU AC | 1,500W | 2,500–3,500W |
| 16,000 BTU AC | 1,800W | 3,000–4,500W |
| Microwave | 1,000W | 1,000W |
| Battery charger (20A) | 300W | 300W |
AC compressors draw 2–3× running watts at startup. Size generator for surge, not running. Soft-start kits reduce surge—allows smaller generator.
Add running watts of all AC loads. Add startup surge for biggest motor (typically AC). 13,500 BTU marine AC: ~1,500W running, 2,500–3,500W startup.
AC load (1,500W) + refrigeration (200W) + battery charger (300W) + outlets (500W) = base. Add 2× for AC startup surge. Size generator above total.
Soft-start kits reduce AC startup surge. Without one, size for startup. With soft-start, smaller generators may work.
Related: 30A vs 50A Shore Power · RV generator sizing.
If you're diagnosing RV electrical or appliance problems, these guides may help:
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Last updated: March 2026 · Reviewed for technical accuracy