Fan Power
Calculator
Results
- Air power (W)
- 83.333333
- Fan shaft power (W)
- 128.205128
- Fan shaft power (kW)
- 0.128205
HVAC and plumbing results
| Air power (W) | 83.333333 |
| Fan shaft power (W) | 128.205128 |
| Fan shaft power (kW) | 0.128205 |
formula-map diagram
- Air power (W)
- 83.333333
- Fan shaft power (W)
- 128.205128
- Fan shaft power (kW)
- 0.128205
HVAC and plumbing relationship
Formula
P = Q × Δp ÷ η= 83.333333333333
Note
This is a simplified model: it applies a standard engineering formula to the numbers you entered. Conversions between BTU/h and kW use the exact factor 1 kW = 3412.142 BTU/h, but every sizing figure is an estimate. Air conditioner sizing uses the common 20 BTU/h per square foot rule of thumb, not a room-by-room load calculation, and it ignores insulation, glazing, orientation, ceiling height, infiltration and local climate. Heating loads use a single volumetric heat-loss factor in W/m³·K rather than a fabric-by-fabric U-value calculation. Air properties are fixed at 1.2 kg/m³ and water at 1000 kg/m³ and 4186 J/kg·K, with no correction for temperature, altitude or glycol. Duct and pipe results use the ideal continuity equation and ignore fittings, bends, roughness and system effect unless you enter those losses yourself. The Hazen-Williams equation is valid only for water in full turbulent flow at ordinary temperatures. Water hammer uses the Joukowsky surge, an upper bound for instant closure. Tank drainage assumes a prismatic tank and steady free discharge. Hot water recovery and condensate figures ignore standing losses and coil bypass. Size real systems with a proper heat-loss survey and have the work checked by a qualified HVAC or plumbing professional.
More in HVAC and plumbing
See all →Frequently asked questions
What inputs determine a fan's power requirement?+
Fan power depends primarily on the airflow rate (CFM) it must move and the static pressure it must overcome, along with the fan's mechanical and motor efficiency — moving more air, or pushing it through more resistance, both require more power.
Why does static pressure matter as much as airflow?+
Power requirement rises roughly in proportion to airflow multiplied by pressure, so a fan pushing air through a restrictive, high-resistance duct system needs significantly more power than one moving the same CFM through an unobstructed path.
What's the difference between the power calculated and what a fan's motor actually draws from the wall?+
The calculated air power is the theoretical minimum energy needed to move that air against that pressure. The motor draws more than this because no fan is 100% efficient — total efficiency (fan efficiency times motor efficiency) determines the gap between theoretical and actual power draw.
How does duct restriction affect fan energy costs over time?+
A dirty filter, undersized ductwork, or too many bends increases static pressure, which raises the power the fan must deliver to maintain the same airflow — this is why a fan can draw noticeably more electricity in a poorly maintained system even without any change in its rated CFM.
Why would I choose a larger fan than the minimum calculated power suggests?+
Selecting some headroom above the calculated requirement accounts for future duct restriction from dust buildup, filter loading, and manufacturing tolerances, and keeps the fan operating in a more efficient part of its performance curve rather than at its absolute limit.