How to Size a Generator for a Chicken Farm: Step-by-Step Calculation

To size a generator for a chicken farm, calculate the electrical loads that run together, then check the motor-starting demand against the generator’s transient capability. Match the voltage, phase, and operating duty before selecting a model. Barn size or bird count alone will not give you a dependable generator size.

Ventilation drives the necessity of this sizing step. An enclosed poultry barn rapidly loses ventilation during an outage, and a power unit that handles baseline lighting yet bogs down as heavy ventilation engages will fail to safeguard the flock. Establishing a clear equipment schedule provides the supplier with the necessary technical figures for accurate model selection.

Step 1: List Everything the Generator Must Power

Start with the barn’s electrical drawings, the controller documentation, and each motor nameplate. Include equipment outside the barn if it will use the same generator:

• tunnel, sidewall and minimum-ventilation fans

• circulation fans and cooling-pad pumps

• feed lines, feed-bin augers and egg-collection or manure belts

• water pumps, water-treatment equipment and egg coolers

• controllers, alarms, inlet or curtain actuators and lighting

• other connected farm loads

Record voltage, phase, frequency, horsepower or input power, full-load current, efficiency, power factor and starting method. Identify which loads run together and which can start at the same time.

Do not confuse heating fuel with electrical demand. A propane or natural-gas brooder or heater supplies heat through combustion, and its BTU/h rating is not an equivalent electrical load to add to the generator. Its blowers, igniters, and controls still count. Electric heaters or heat lamps, if fitted, must be included at their actual electrical input.

Seasonal operating conditions must also be factored into the sizing model. Ventilation controllers stage additional fans as temperatures rise, placing maximum continuous demand on the generator during extreme summer heat when the full cooling system operates. Winter power requirements drop significantly, focusing primarily on baseline ventilation. Always configure sizing around the peak demand scenario the power unit must handle, using verified documentation and equipment specs for your specific facility, including any subsequent upgrades.

Step 2: Convert Motor Output to Electrical Input

Motor horsepower normally describes mechanical output at the shaft. The generator must also supply the energy lost inside the motor.

For an illustrative full-load estimate:

Motor input kW = horsepower × 0.746 ÷ motor efficiency

Enter efficiency as a decimal. A hypothetical 1.5 hp tunnel-fan motor operating at rated output with 75% efficiency needs:

1.5 × 0.746 ÷ 0.75 = 1.49 kW of electrical input

Power factor is a separate consideration:

Running kVA = input kW ÷ power factor

At an assumed running power factor of 0.85:

1.49 ÷ 0.85 = 1.76 kVA

Efficiency connects mechanical output to electrical input. Power factor connects real electrical power, measured in kW, to apparent power, measured in kVA. Do not use one in place of the other.

Where reliable measured input is available for the operating condition, use it instead of converting horsepower again. Part-load efficiency and power factor can differ from nameplate full-load values, and small single-phase fan motors often vary more than people expect.

Step 3: Calculate the Simultaneous Running Load

Here is a hypothetical load schedule for a single barn on single-phase power. These are teaching assumptions, not specifications for a particular barn or a Toews Power installation.

Totals use unrounded intermediate values. Adding individual kVA values is a conservative planning sum; a detailed calculation combines real and reactive power using each load’s characteristics. In a real barn, the bin auger and feed lines may not run during peak ventilation, so ask which loads genuinely overlap.

This gives you the running-load baseline. It does not prove that a 24 kW or 28 kVA generator can start the system.

As Cummins explains in its generator application manual, a generator has both engine-power and alternator volt-ampere limits. Both matter during changing loads.

Step 4: Check Motor Starting Separately

Use manufacturer locked-rotor current, a verified motor code letter, or starter data to calculate the starting requirement. A blanket multiplier cannot capture every motor and driven load.

For a balanced three-phase load:

kVA = 1.732 × line-to-line volts × line amps ÷ 1,000

For single-phase equipment:

kVA = volts × amps ÷ 1,000

Suppose one example tunnel fan operates at 240 V single-phase and its verified starting current is 40 A. Its approximate initial starting demand is:

240 × 40 ÷ 1,000 = 9.6 kVA

That is far above its 1.76 kVA running demand. If a controller started all eight tunnel fans at the same instant, the combined demand would be roughly 76.8 kVA. That does not automatically mean buying a generator rated at 77 kVA continuously. The supplier still needs to check the chosen alternator's motor-starting capability, engine response, allowable voltage and frequency dip, and motor acceleration time.

Do not multiply starting kVA by the running power factor to claim a precise starting kW value. Starting power factor and torque requirements differ. The manufacturer’s transient analysis needs those starting characteristics.

Step 5: Model the Actual Starting Sequence

Starting the largest motor while little else is connected can reduce the demand imposed on an already-loaded generator. Cummins identifies staged loading as one way to manage generator sizing.

Barn controllers often stage fans already, which can work in your favour. Ask the controller and equipment supplier what stage delays are set and whether they can be changed without compromising ventilation. Airflow requirements, bird welfare and equipment safety interlocks must remain intact.

For the example, the supplier might evaluate:

1. Controls, alarms and lighting energize.

2. Minimum-ventilation fans start.

3. Tunnel fans stage in as barn temperature rises.

4. Feed lines, the bin auger and the water pump start on their normal schedule.

Each step needs a check. The largest single motor does not necessarily create the worst event if several fans stage in while the rest of the barn is fully loaded.

Document the precise operating behavior during power loss and transfer events. Generator cranking intervals, transfer switch delay times, and automated equipment re-engagement directly determine how rapidly ventilation resumes. Implementing a staged startup model becomes ineffective if fan motor contactors reclose simultaneously upon power restoration. Evaluate controller reboot sequences, staggered starting timers, and alarm signaling as part of the facility plan.

Step 6: Confirm Supply, Duty and Site Conditions

A generator with enough kW can still be the wrong equipment.

Verify the facility's true utility voltage, phase configuration, and operating frequency. Single-phase service cannot be substituted for three-phase capacity, and altering alternator lead connections directly impacts available power output. Integrating transformers, phase converters, or secondary power conditioning introduces distinct electrical factors into the calculation.

Clarify the expected operational role of the power unit. Brief emergency standby duty demands a different power unit profile than continuous operation through multi-day grid failures. Match your load profile to the manufacturer's primary or standby output continuous-duty thresholds rather than relying on max standby nameplates for sustained running. On-site fuel storage capabilities must also be verified, as a properly matched generator remains ineffective if on-site fuel reserves fail during a prolonged outage.

Elevated site altitude, high ambient temperatures, and restricted enclosure ventilation cause measurable generator derating. As Cummins details in its application engineering documentation, environmental deratings must be calculated using exact manufacturer curves rather than generic correction factors. Atmospheric dust, moisture, and engine exhaust orientation present serious operational risks. Ensure engine exhaust remains fully isolated from building air intake louvers, and verify installation clearance with your generator distributor and certified electrical contractor.

When planning variable-frequency drives or solid-state soft starters for large fan motors, request a comprehensive application review from the supplier. Lowering motor inrush current helps control transient dip, but total starting torque, harmonic distortion, and alternator excitation stability require thorough technical verification.

What to Send Toews Power

Toews Power supplies standby and primary power generators for agricultural and other applications. For a useful sizing discussion, send:

• barn layout, number of barns and whether they share one service

• electrical drawings and controller model

• fan schedule with clear motor-nameplate photographs and starter details

• the running-load schedule and required startup sequence

• site voltage, phase, frequency and expected outage duration to cover

• other connected loads and any definite expansion plans

Ask for a recommendation supported by the actual load steps and site conditions. Have a qualified electrical contractor plan the connection, transfer equipment and installation. This calculation is not wiring guidance.

Frequently Asked Questions

Can I size the generator from the number of birds?

No. Barns with similar bird counts can have different fan counts, heating systems and auxiliary equipment. Start with the electrical specifications.

Is a 20% allowance enough for motor starting?

Not reliably. An allowance above running demand does not prove that the generator can handle the starting transient. Check the motor-starting data and generator response separately.

Can I back up only some of the fans?

Possibly, but that is a ventilation design decision as much as an electrical one. Bird age, weather and barn design all affect how much airflow is needed, so confirm the plan with your equipment supplier before sizing the generator around it..

Get the Load Schedule Checked Before You Order

Send the equipment details before asking for a generator recommendation. Contact Toews Power with your barn specifications and operating plan to discuss a generator that can handle both startup and the work that follows.