# Frequent question: How do you size a fan motor?

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## How do you match a fan blade to a motor?

Using the specifications of the fan blade is the best way to determine the correct horsepower for a replacement condenser fan motor. The diameter, angle and number of fan blades, along with the RPM of the motor, are the pieces of information necessary to make this determination.

## How is fan motor power calculated?

Divide the fan’s power consumption, measured in kilowatts, by 0.746 to convert it to horsepower. If, for instance, a fan consumes 4 kW: 4 / 0.746 = 5.36 horsepower. Multiply the result by the fan’s efficiency. If the fan operates, for instance, at 80 percent efficiency: 5.36 x 0.80 = 4.29 horsepower.

## How do I know my HP fan motor?

Step-1 Formulas:

1. When total static pressure and overall efficiency are defined, fan input power is: Pf = Vf ΔPs K1 / (ηo)
2. When motor brake horsepower is defined, input power is: Pf = BHP * K2 / ( ηe )
3. Brake Horsepower: BHP = ( ηe * Pf ) / K2.
4. Fan input power at part-load: Pf,pl = [(Pf,fl) (Rpl)] / 100.

## Are fan motors interchangeable?

They are not interchangeable. If you can’t read the label on the old motor, take it apart and look at the number of poles. A 6 pole motor will be a 1075 RPM motor and an 8 pole motor will be an 850 RPM motor.

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## Is my fan blade CW or CCW?

Look at the blade that is in the 12 o’clock position. One side of the blade will be resting on the floor and one side will be raised. – If the Right side is raised, then your fan is Clockwise. – If the Left side is raised, then your fan is CounterClockwise.

## How do you measure a replacement fan blade?

Standing on a step ladder as needed, hold one end of a tape measure to the tip of a fan blade on a fully assembled fan. If the unit has an even number of ceiling fan blades, extend the tape measure to the end of the opposite blade and record the distance from tip to tip. This is the diameter.

## How do you calculate motor efficiency?

Efficiency is simply output (useful) power divided by input power, with the difference being losses due to imperfections in design and other inevitabilities. Efficiency in this context is a decimal varying from 0 to 1.0, or sometimes a percentage.

## How much power does a fan use?

On average, fans use 0.0393 kWh of electricity per hour, 0.3144 kWh per night, 0.943 kWh per week running 24/7 and 28.3 kWh per month if left on 24/7.

## How do you convert CFM to HP?

CFM can be converted into HP by multiplying the airflow by 1.6 and then multiplying that result by 0.9.

## What is the fan law?

The Fan Laws are a group of useful equations for determining the effects of a change in the speed, the diameter of the fan and the density of air in the system. They are most useful for determining the impact of extrapolating from a known fan performance to a desired performance.

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## How is blower power calculated?

Power is the rate of work in a time: P = F·v, where P = power; F = force; and v = velocity, ft/min.

## How is fan shaft power calculated?

Now that you know the fan area it is time to multiply it by the air speed of the fan. This will give you the air flow in CFM (or cubic feet per minute). Determine the horsepower. In order to find the horsepower, multiply the air flow by the total pressure and divide the result by 6356.

## Can you replace a fan motor?

If the motor does turn out to actually be the problem, you can certainly replace it. Some motors simply plug in and out of the fan. If you’re not lucky enough to have one of those, you’ll have to wire the new motor into place, matching the colored wires.

## Do fan motors wear out?

Like any home appliance, ceiling fans wear out as they age. Motors can quit working, wires can become loose or broken, and blades can become worn.