Whole House Fan Calculator
Fan size and attic outlet area for night-flush cooling of an entire home.
Without enough attic outlet the fan just pressurizes the attic and pushes hot air back down. 1 m² of net free vent per 1,000 L/s is the safe line.
Formula
Whole House Fan Calculator is a free whole house fan size for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Whole House Fan Calculator
Fan size and attic outlet area for night-flush cooling of an entire home. The calculation implements Q ≈ 30 ACH; outlet area = Q/1.0 m/s net free area (Davis Energy Group / Title 24 whole-house fan guidance). Without enough attic outlet the fan just pressurizes the attic and pushes hot air back down. 1 m² of net free vent per 1,000 L/s is the safe line.
How to use Whole House Fan Calculator
- 1Enter Conditioned floor area in m².
- 2Enter Average ceiling height in m.
- 3Read Fan size (≈ 30 volume changes/h), Net attic outlet area needed instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Whole House Fan Calculator?
- ✓Implements the standard formula — Q ≈ 30 ACH; outlet area = Q/1.0 m/s net free area
- ✓Reference cited on-page: Davis Energy Group / Title 24 whole-house fan guidance
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Whole House Fan Calculator use?+
It computes Q ≈ 30 ACH; outlet area = Q/1.0 m/s net free area, per Davis Energy Group / Title 24 whole-house fan guidance. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Without enough attic outlet the fan just pressurizes the attic and pushes hot air back down. 1 m² of net free vent per 1,000 L/s is the safe line.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Whole House Fan Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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