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Calculation Machine

Battery Room Ventilation Calculator

Hydrogen dilution airflow for battery banks.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Required ventilation
12.9 CFM
With 25% safety factor
16.1 CFM
Air changes provided
0.65
Minimum 1 ACH
20 CFM
Design airflow
20 CFM

Quick answer

Battery ventilation is based on hydrogen evolution during charging, sized to hold concentration under 1% by volume.

The formula

CFM = 0.0269 x cells x charge current (per IEEE)

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Number of cells24
  • Charge current20 A
  • Room volume1200 cu ft

Result

  • Required ventilation12.9 CFM
  • With 25% safety factor16.1 CFM
  • Air changes provided0.65
  • Minimum 1 ACH20 CFM
  • Design airflow20 CFM

How to use the Battery Room Ventilation Calculator

  1. 1Count the cells and take the maximum charge current from the charger nameplate.
  2. 2Compare the hydrogen-based figure with a 1 ACH minimum and use the larger.
  3. 3Place the exhaust point high — hydrogen collects at the ceiling.

Frequently asked questions

Do sealed AGM batteries need this?

Much less, but valve-regulated cells still vent under overcharge, so codes often still require ventilation.

What is the danger threshold?

Hydrogen is flammable at 4% in air; designs target 1% for a wide margin.

About this calculator