Choosing the Right Generator Size: Why It Matters More Than You Think

usedgear4sale
Apr 28
2 min read

Whether you’re running a jobsite, powering a pump, or setting up temporary power at home, generator sizing isn’t something to guess at. Choosing the wrong size can lead to poor performance, wasted fuel, or even serious engine damage.

At Puget Sound Equipment Sales, one of the most common issues we see is customers renting generators that are either too small—or more often, way too big for the job.

Let’s break down why getting it right matters, especially here in the Pacific Northwest.

The Risks of Choosing the Wrong Generator Size

Wet Stacking, The Number 1 Killer of Diesel Generators

Wet stacking happens when a diesel generator runs at too low of a load for extended periods. The engine never gets hot enough to burn fuel completely, leading to:

Unburned fuel buildup in the exhaust
Carbon deposits in injectors and cylinders
Reduced engine life
Smoky, inefficient operation

👉 Most diesel generators should run at at least 30–40% of their rated load to avoid this.

Key Concepts (Made Simple)

Running Watts (kW) → What your equipment needs to operate
Starting Watts (Surge) → Extra power needed to start motors
Load Type → Resistive (lights, heaters) vs. inductive (motors, pumps)

👉 Motors can require 2–3x their running wattage during startup.

What You Should Tell Your Rental Provider

To get the right generator—and avoid headaches—come prepared with this info:

1. Equipment List

Be specific. Include everything you plan to run:

Pumps (size, HP, voltage, phase)
Air compressors
Heaters
Lighting
Tools or trailers

2. Electrical Details

For each piece of equipment, provide:

Voltage (120V, 240V, 480V, etc.)
Phase (single-phase or 3-phase)
Amps or kW rating
Motor horsepower (if applicable)

👉 A nameplate photo goes a long way.

3. Starting vs Running Load

Let your provider know:

What equipment starts first
What runs continuously
If multiple motors start at the same time

This helps prevent overload during startup.

4. Runtime Expectations

How many hours per day?
Continuous or intermittent use?

This affects fuel planning and generator selection.

The Bottom Line

Choosing the right generator size isn’t just about having “enough power”—it’s about running efficiently, protecting your equipment, and avoiding preventable issues like wet stacking.

If you’re not sure what size you need, bring your equipment info (or even photos), and we’ll help you dial it in so your job runs smoothly from the start.