How to size a whole house fan for your home
What size whole house fan do you need? Match your home's square footage and number of stories to the sizing tables below, where we list the exact Centric Air and QA Deluxe model for every home size. Or skip the tables: enter your square footage and stories in the configurator and it returns your sized recommendation in seconds.
Choosing the wrong size whole house fan is the single most common mistake homeowners make. Too small and the fan can't cool your home effectively. Too large and you're overspending on capacity you can't use. This guide shows you exactly what size your home needs, by stories and square footage.
The reason two-story homes need more airflow: hot air rises. The upper floor of a two-story home is consistently 5–10°F hotter than the lower floor. The fan needs extra force to pull that heat through the ceiling and out the attic.
Single-story sizing table
| Home Size | Centric Air (Premium) | QA Deluxe (Standard) | ECM Option |
|---|---|---|---|
| 0–900 sq ft | Centric Air 2.0 | QA Deluxe 3300 | — |
| 901–1,350 sq ft | Centric Air 2.7 | QA Deluxe 5500 | QA Deluxe 4800 ECM |
| 1,351–1,800 sq ft | Centric Air 3.4 | QA Deluxe 5500 | QA Deluxe 4800 ECM |
| 1,801–2,400 sq ft | Centric Air 3.4 | QA Deluxe 5500 | — |
| 2,401+ sq ft | Centric Air 4.0 | QA Deluxe 6500 | Centric Air ECM 4.0 |
Two-story sizing table
| Home Size | Centric Air (Premium) | QA Deluxe (Standard) | ECM Option |
|---|---|---|---|
| 0–1,400 sq ft | Centric Air 2.0 | QA Deluxe 3300 | — |
| 1,401–1,450 sq ft | Centric Air 2.7 | QA Deluxe 3300 | — |
| 1,451–1,800 sq ft | Centric Air 2.7 | QA Deluxe 5500 | QA Deluxe 4800 ECM |
| 1,801–2,800 sq ft | Centric Air 3.4 | QA Deluxe 5500 | QA Deluxe 4800 ECM |
| 2,801–3,400 sq ft | Centric Air 3.4 | QA Deluxe 5500 | — |
| 3,401+ sq ft | Centric Air 4.0 | QA Deluxe 6500 | Centric Air ECM 4.0 |
The attic ventilation factor
Your fan's actual performance depends not just on its CFM rating, but on how easily air can escape through your attic vents. This is called Net Free Area (NFA) — the actual open area through which air can pass.
The rule: 1 sq ft of NFA per 750 CFM of fan airflow. A 3,000 CFM fan needs at least 4 sq ft of NFA in your attic venting system.
How to check your existing ventilation
- Locate your soffit, ridge, and gable vents (most homes have at least two of these)
- Find the NFA rating on the vent — it's usually stamped on the product or on the packaging
- Add up all your attic vents' NFA ratings
- Compare the total to your required NFA (fan CFM ÷ 750)
Most homes are adequately vented. If your home has standard soffit and ridge vents, you likely already have enough NFA. The most common exception is older homes with only gable vents. If you're undersized, adding a single gable vent is usually an inexpensive fix.
Climate zone adjustments
In extremely hot climates where attic temperatures exceed 130°F regularly (deep Southwest desert), consider sizing up one tier in the table above. The fan has to work harder to push heat through a very hot attic. In mild coastal climates, the standard sizing in the table is entirely sufficient.
When to size down
Some homeowners have open floor plans with very high ceilings (12 ft+). In this case, calculate by volume rather than area: multiply your square footage by ceiling height and divide by 8 (standard ceiling height) to get the equivalent "standard" square footage.
Example: 2,000 sq ft with 12-ft ceilings = 2,000 × (12÷8) = 3,000 sq ft equivalent. Use the higher number when reading the sizing tables above.