What You Should Know About EPA Diesel Emissions Tiers

This open skid generator meets EPA Tier 4 emissions standards.

Over the last few decades, the EPA has put into place stricter environmental standards on many types of equipment, such as non-road engines — which includes those used in generators, or gensets. These EPA tier ratings affect every classification of generators built since the 1970s.

If you are in the market as a first-time buyer of a genset or looking to replace an older model, this discussion about EPA emission standards for diesel generators may not seem applicable to you. However, it is quite to the contrary; it’s essential you understand these standards because they will help ensure you buy the correct generator for your needs.

Let’s take a closer look at the ratings and how they can play a part in which generator you buy.


What are EPA Tier Diesel Emissions Tiers?

In an effort to reduce harmful emissions, and improve air quality, the U.S. government began to implement regulations in the 1950s, which culminated in the establishment of the Environmental Protection Agency (EPA) and the passage of the Clean Air Act in 1970. These standards would impact on and off-road vehicles and engines, including those built for generator use. A formal tiered structure was undertaken across several years to help manufacturers develop technologies necessary to achieve the regulatory goals.

Tier 1

This first federal standard, published in 1991 and implemented in 1996, focused on diesel engines over 50 hp. It set goals to limit harmful gases such as NOx (nitrogen oxides) by 27% before 2010 and 37% by 2025. To help you further understand the tiers and the gensets they affect according to their horsepower (HP), take a look at the EPA diesel engine chart.

Tiers 2 and 3

Both second and third tiers introduced stricter regulations beginning in 1998 with Tier 2. This phase addressed carbon monoxide, unburned hydrocarbons and NOx along with emitted particulate matter (PM). While Tier 2 covered engines of all sizes manufactured between 2001 and 2005, Tier 3 was specific to engines with 50 to 750 hp. Tier 3 further restricted exhaust emissions and was implemented from 2006-2008.

Tier 4

Deemed the last phase and signed in 2004, Tier 4 set the transition to run from 2008 to 2015 with a 90% reduction in PM and NOx as the new standard. A new ultra-low sulfur diesel fuel would be required to achieve this target, along with the need for manufacturers to establish advanced engine technologies and innovative after-treatment of exhaust gas.

It is through this final transition period that the Environmental Protection Agency provided machine builders a few additional years until 2020 or 2021 to meet regulations. The government further stipulated that manufacturers with an existing inventory of Tier 1, 2, or 3 engines would be permitted to continue to use these engines in their generators until the stock is consumed.

Emergency Versus Non-Emergency Generator Standards

There was one important exception made between emergency and non-emergency generators regarding the Tier 4 regulations.  Standby (emergency) gensets, which are those used for temporary purposes, are exempt from Tier 4 emissions standards and are only subject to Tiers 2 and 3. Prime on-site generators, on the other hand, should meet Tier 4 standards.

It is vital to note, although there are federal exceptions to Tier 4 standards, local ordinances take precedence over the use of diesel gensets. Therefore, it is essential that you check your regional regulations to ensure your generator is compliant.

How Does This Tier Information Help You?

If you are environmentally conscious, you will want your genset to meet Tier 4 standards, as they are the strictest of all the tiers. The advancements in control technologies used in Tier 4 diesel engines result in near-zero emission levels. In part because of the EPA Tier ratings for non-road diesel engines, NOx saw a 62% reduction during the period from 1980 to 2018, whereas Direct PM2.5 declined by 30% between 1990 and 2018, according to the EPA.

Along with helping to improve air quality,  Tier 4 generators offer several advantages to you as a consumer including:

  • Quiet and smooth operation
  • Increase in fuel efficiency
  • Advanced performance technologies
  • Less maintenance
  • Lower operating costs

What the Future Holds

Although it’s considered the final rating, many countries and manufacturers are looking past Tier 4 to a possible Tier 5 in the future. If and when the EPA moves toward the next tier, most expect the agency to continue its focus on more advanced technologies that will result in a greater reduction in emissions and an increase in genset efficiency.

Look to the General Power Team for Your Next Generator

We know that tier ratings can be confusing and misunderstood. However, we also recognize it is important that you purchase the highest-quality generator for your home or business. Don’t settle for anything less than the best. We can answer your questions, so please contact General Power’s team for more help with your generator needs.