What a planning estimate is good for
- Comparing options. Diesel heater vs electric, 200 Ah vs 400 Ah, fixed bed vs lift.
- Budget. Roughly what each system costs and where the money goes.
- Layout. How much space a battery bank, inverter or water tank needs.
- Spotting conflicts early. Payload getting tight, a power budget that doesn't close, a fan that would sit under a solar panel.
- Knowing what to ask. Which parts of your build will need a professional.
What a planning estimate isn't
- A wire and fuse spec to install from.
- A load rating for a mount or a bed.
- A heat-loss calculation for final heater sizing.
- Approval of anything by anyone.
What it depends on
How close an estimate gets to reality depends on what it's built from:
- Assumptions: typical draw, typical weight, typical sun hours. Useful for choosing, loose for building.
- Manufacturer specs: the exact product's manual. Better.
- Your measurements: cable run lengths, scale weights, interior dimensions. Better again.
- A professional's design and review: what you build the high-risk parts from.
Most of a build moves from the top of that list toward the bottom as decisions get made.
Worked sample (planning estimates)
A 2,000 W inverter on a 12 V system.
The planning estimate:
- 2,000 W ÷ 12 V ≈ 167 A.
- Inverters lose some power converting. At an assumed 90% efficiency, about 185 A at the battery.
That's enough to plan with. It tells you this is a very high-current run, that it needs heavy cable and a large fuse, and that the inverter should sit close to the battery. You can now budget for it, leave room for it in the layout, and know it's a job to get help with.
The professional design adds:
- The exact inverter's manual: its required cable size, fuse type and size, and terminal torque.
- The measured cable run, which changes cable size.
- A main fuse rated for the fault current a lithium battery can deliver.
- Correct grounding and how the inverter's AC output is wired.
- A qualified person who designs or checks it before it's connected.
Same inverter. The estimate tells you what you're dealing with. The design is what you build from.
When to get a professional
Briefly, the parts of a van build to hand to a qualified professional, or at least have one design or check:
- High-current DC: battery main cables and fusing, the inverter, the alternator charging run.
- Anything on 120 V AC, including shore power.
- Seats and seat belts.
- Roof or body cuts that touch structure.
- Fuel, propane and exhaust.
How Vansembly labels numbers
Vansembly marks its numbers as planning estimates and keeps what still needs checking visible. It's planning support, not a professional stamp.