Generator Sizing Guide

Ownership a generator is typically a significant investment for a home or business owner. It'south as well something most consumers don't do very often, so there'southward a lot of confusion around which fuel type to employ (diesel, natural gas, propane), which brand is best (Caterpillar, Cummins, MTU, Generac, Kohler, HIPOWER), and almost peculiarly, what size generator is appropriate.

To respond that last question, your first and all-time option is e'er to consult a certified electrician to appraise your specific needs. Nevertheless, if yous opt to do information technology yourself, yous can yet brand an informed generator purchase or rental by post-obit a few basic guidelines. Nosotros're laying those out in this guide to aid you know how to determine what size generator you need.

Cummins generator Cat C15 generator set HIPOWER Generator Cat Generators

Generator Classes: Residential vs. Industrial

You lot should already have an idea of what class of generator y'all need. If you're a homeowner looking for backup or standby power, you need either a small, portable generator or a stationary standby generator. These sizes run from 2kW-2000 watts or less for a recreational unit, up to about 50kW for a whole-house standby generator. These generators typically use a single-phase electric current, which are sufficient to power smaller equipment that don't require abiding, high-voltage power.

Industrial generators are available in a range of sizes, from around 20kW to well over 3MW. Larger business organization and industrial applications obviously require more chapters and thus often utilise three-phase motors for college power. Role buildings, manufacturing facilities, data centers, and building complexes such as shopping malls, educational institutions, and living centers all require larger-capacity generators. This is the example whether it's regarding primary power supply or emergency dorsum-up power generation.

Cat Olympian Residential GeneratorData Center Generator

How to Size a Generator

The basic generator sizing formula goes similar this:

  1. Grade a list of all items that will be powered.
  2. Decide the starting wattage (energy needed to turn it on) and running wattage (energy needed to operate information technology) for each piece of equipment. These figures are typically inscribed somewhere on the equipment itself, equally well every bit recorded in the owner's manual.
  3. Calculate your full power requirement past adding up these kW or KVA figures.

Click here to employ our Ability Estimator

For equipment rated in amperes, you can catechumen amps to watts with the post-obit formula:

  • For resistive loads (nigh mutual type): Wattage = amperes ten volts
  • For reactive loads: Wattage = amperes x volts 10 load cistron

Load factor is the ratio of your electric energy use in kilowatt-hours to your peak need in kilowatts. You lot can calculate it by consulting your utility bill for data and using it in the post-obit formula:

  • Total kWh for the previous month / (your pinnacle demand for the period 10 30 days x 24 hours)

Fifty-fifty if you lose the manual, you should exist able to find wattage details online. However, if you can't decide a piece of equipment'south ability draw figures, you tin can use a ballpark number. For example, these are the starting and running figures for some common tools and electronics:

Appliance Starting Load (West) Running Load (W)
Air compressor 4000 2000
Disc grinder 4000 2000
Router 1500 600
Electric chainsaw 2400 1200
Table saw 4500 1800
Water heater 4500 4500
Laptop 250 250
Printer 500 500
Air conditioner (10k BTU) 2200 1500
Dishwasher 1450 1400
LCD Tv (55") 230 230

One time you lot know the estimated wattage needed, the generator size is easier to choose. Whatever number you lot come up upwards with, cull a generator with a chapters that'south x-20% larger than your requirement . This will give you lot some leeway when and if you update your equipment and finish upwardly needing more than ability as a outcome. It also helps you manage "de-rating," or under performance of the generator compared to its manufacturer-claimed abilities due to agin operating atmospheric condition, such as extreme temperatures or high altitudes.

Generator sizing tip

Buying a Unmarried Generator vs. Paralleling

If your power needs are big enough, you may wonder whether information technology'southward better to go with a single, huge diesel fuel generator, or split the burden between two or more than smaller generators. For example, instead of a 1200kW generator, you could install three 400kW generators. This is called paralleling, and it can be a great option in the right circumstances. Here'south why:

#ane. Greater flexibility. It's very likely the reason you lot're ownership a generator at all is the boosted reliability, a hedge against an interrupted power supply causing a slowdown or halt to your business's operations. With multiple generators, you lot don't have to worry if 1 has to be close down for maintenance. Yous just shift the brunt to the others and keep correct on working.

With just ane generator, if information technology has to finish, so do yous.

#2. Can be more cost-effective. Manifestly the economic science will vary widely depending on brands, new vs. used generators, prices in your geographic location, etc. But all things being equal, once you alienation a certain generator size, it becomes more than economical to parallel than employ a unmarried unit. Specifically, once you go over the sizes of gas or diesel engines mass-produced for employ in cars, also, those engines are harder to come by and are thus more expensive. And the engine comprises more than than one-half the toll of a generator.

The threshold for diesel fuel engines is 600kW and for gas engines it's 150kW.

#3. Can be more than practical. Depending on your physical infinite, it may be easier to fit two or three parallel generators into a room than 1 oversized unit. Among large commercial generators, smaller capacities can mean the difference in 25 or more square feet per unit.

#4. Easier on the generators. Load sharing among two or more generators can extend the life of each generator and avert the risk of overburdening a single unit. For continuous usage, loads up to 80% generator capacity are ideal.

Demand Help Sizing Your Generator?
WPP Is Here to Aid!

  • WPP has the engineering and technical expertise to properly size and custom package the right ability solution to fit you unique applications.
  • For Commercial, Industrial, Municipal, Marine and Oil & Gas applications.
  • Improve the reliability of your power, increase the life span of your equipment, and lower your maintenance costs.

Get Assistance Sizing Your Generator

Generator Sizing and Fuel Consumption

In the same manner a 3500-level truck uses more fuel than a 1500, larger generators consume fuel faster than smaller units. This is important to remember when "running the numbers" on what a new or used generator may cost. Not only do you take to refuel larger generators more than ofttimes, it may be necessary to store extra fuel on-site, precipitating the need for boosted storage tanks.

For this reason, when it comes to residential generators, Consumer Reports recommends getting the smallest portable or home standby generator that meets your needs to limit the corporeality of fuel you have to store to run information technology.

For industrial-strength generators, consult our approximate diesel fuel consumption nautical chart to estimate how much fuel you lot'll burn down in a particular generator size operated at either a quarter-, half-, 3-quarter, or total load.

Why It's Crucial to Choose the Right Generator Size

It may be tempting to skimp on the size of your generator, especially when doing so might save you a couple one thousand dollars. However, selecting a generator that's too small for your applications is a recipe for disaster. Not merely tin can yous harm the appliances and devices pulling ability from the generator, you can harm the generator itself.

Here are some more benefits of erring on the side of a generator that'southward too powerful, as opposed to likewise weak:

  • Increased usable life of the generator
  • Consistent production performance
  • Limited incidence of capacity overloads
  • Express incidence of unexpected organization failures
  • Reduced likelihood of asset damage
  • Increased personnel rubber
  • Decreased risk of overheating and electrical fires
  • Reduction in frequency and cost of maintenance
  • Increased ease and speed of maintenance