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Toilet fan battery calculator

Budget ventilation energy and rated battery capacity for a period without charging.

No account needed. Results update here as you change the inputs. Measurements stay in this tab unless you choose to share a link; shared links contain the inputs, including any location coordinates.

Your inputs

The starting values are examples. Replace them with your own measurements, prices or documented requirements.

What to have ready
  • Fan input watts and the manufacturer-required daily duty.
  • Days without charging and nominal battery voltage.
  • The Ah actually allocated to the fan, after allowing for other equipment separately.
Measurements for Toilet fan battery calculator

Calculated from your inputs

Your plan

The example will calculate here when JavaScript is ready.

What to do next

    Calculation details

    Inputs used in this result

    Compare a change before committing

    Keep this plan, change the inputs and see the difference. The comparison stays in this tab.

    Does the fan’s allocated battery cover the period without charging?

    A small fan can be a continuous load. This toilet fan power calculator turns the entered watts and required operating hours into daily energy, then applies losses and reserve to the battery capacity needed for the uncharged period.

    The available-allocation field lets you check whether the fan’s share of a battery is large enough. It deliberately excludes the rest of the van or cabin loads, so do not confuse a fan-only result with a complete electrical plan.

    How to use this planner

    1. Enter the required ventilation schedule rather than reducing it to fit a battery.
    2. Set the uncharged period, losses and reserve.
    3. Read the capacity needed and days covered, then check the complete electrical system separately.

    The calculation

    Daily Wh = watts × hours. Rated battery Wh = daily Wh × days ÷ efficiency ÷ (1 − reserve). Rated Ah = rated Wh ÷ nominal battery voltage.

    A worked example

    A 2 W fan running 24 hours uses 48 Wh/day. Three days at 90% efficiency and 20% reserve need 200 rated Wh, or 16.67 Ah at 12 V.

    Example inputs are demonstrations. Replace them with your own measurements, prices or documented requirements.

    Assumptions and limits

    Follow the manufacturer-required ventilation schedule; reducing hours to save energy may make the installation unsuitable. This budget covers the fan only, without recharging. Battery ageing, cold, other loads, peak output and converter limits need separate checks. Do not count conversion losses twice.

    Questions about this calculation

    Can I turn the fan off for part of the day to reduce the result?

    Only use a duty allowed for your actual model and conditions. This page calculates the entered schedule; it cannot establish that reducing required ventilation is suitable.

    Are solar charging and other loads included?

    No. It is a no-charging fan-only energy model. Charging reliability, other equipment, cold, ageing, supply ratings and wiring require the complete system budget and appropriate installation checks.

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