When it comes to purchasing an industrial generator, one of the most important factors to consider is compliance with EPA emission standards. These rules determine what equipment you can legally operate, how it impacts your project approvals, and even the long-term value of your investment.
Whether you are buying a new or used unit, understanding how Tier regulations apply to diesel and natural gas generators will help you make a smarter decision.
What Are EPA Emission Standards?
The Environmental Protection Agency (EPA) sets strict requirements for nonroad diesel engines used in industrial equipment, including generators. These rules are divided into Tier levels that define how much nitrogen oxides (NOx), particulate matter (PM), hydrocarbons, and carbon monoxide a generator can emit.
- Tier 1–2: Older standards, still found in many used generators.
- Tier 3: Mid-range compliance, common in standby equipment.
- Tier 4 Final: Current strictest standard for new prime and continuous duty generators.
For a deeper look at how these standards are defined, visit the EPA’s official emission standards overview.
Diesel vs Natural Gas Generators
Diesel engines remain the most common choice for large-scale standby power because they are reliable and provide high output. However, they face more restrictive regulations, especially in urban or air-quality-sensitive regions.
Natural gas generators are often seen as a cleaner alternative since they emit fewer particulates. They are also sometimes favored by municipalities and facilities with existing gas infrastructure. However, they may not always be practical for remote sites or operations that require mobile units.
For additional insights on the differences, the U.S. Department of Energy provides updated reports on fuel use and emissions.
Common Buyer Questions About EPA Standards
Can I still buy a used Tier 2 or Tier 3 generator?
Yes. Many organizations purchase Tier 2 or Tier 3 units because they are affordable and dependable for standby applications. The key is to confirm with your local permitting authority that these units are still acceptable for your project.
Do I need Tier 4 Final compliance?
Not in every situation. Tier 4 Final is mandatory for most new generators used as prime or continuous power. If you only need standby backup, earlier Tier levels are often still allowed. Keep in mind that Tier 4 equipment may offer long-term value if your facility is in a region where air quality regulations continue to tighten.
How do rules change for standby vs prime power?
Standby units are generally subject to fewer restrictions because they run fewer hours each year. Prime power and continuous duty applications must meet the highest levels of compliance since they operate regularly under load.
What about exporting generators overseas?
Regulations vary by country. Some markets will accept older Tier levels while others mirror EPA Tier 4 Final requirements. Before exporting, make sure your generator is certified to operate in the receiving country. The U.S. International Trade Administration provides resources on global compliance.
Are diesel generators worse for compliance than natural gas?
Diesel units require more advanced aftertreatment systems to meet Tier 4 standards, but they are still widely used and remain the backbone of industrial power. Natural gas burns cleaner, but infrastructure and availability play a large role in determining if it is the right fit.
Cost and Trade-Offs
- Tier 4 units: Higher upfront cost but fully compliant and designed for long-term operation in regulated markets.
- Used Tier 2/3 units: Lower cost and widely available, but may face restrictions in certain states or industries.
- Fuel choice: Diesel remains the most reliable option for high-capacity standby power, while natural gas is appealing for sites with pipeline access and emissions concerns.
How Generator Source Helps Buyers Stay Compliant
With 50 years of industry experience, Generator Source has helped organizations across construction, healthcare, oil and gas, utilities, and property management navigate the complexities of generator compliance.
Every unit we sell is thoroughly inspected, load bank tested, and documented. Our teams in Colorado, Florida, and Texas are available to provide site-specific recommendations and ensure you select equipment that meets both EPA standards and local permitting requirements.
Final Takeaway
Meeting EPA emission standards is more than a legal requirement. It affects how your generator is permitted, how reliable your system will be, and the overall cost of ownership. Whether you need a high-capacity Tier 4 unit or a dependable Tier 2 standby generator, Generator Source can help you make the right choice.