Building Operating Management

What Tier 4 Emissions Rules For Backup Generators Mean

In 1996, the Environmental Protection Agency (EPA) introduced new emission standards aimed at non-road mobile diesel engines such as construction and agriculture equipment. To be phased in over a four-year period beginning January 2007, these regulations require new stationary diesel engines, including engine generators, to comply with a tiered timing structure of emission allowances. Based on the systems’ engine horsepower rating, generators are rated from Tier 1 to 4, with most non-emergency diesel engine generators required to arrive at Tier 4 by 2012 (see table). Tier 4 requirements are the most stringent.

Because emergency standby engine generators typically operate for a low number of hours, EPA exempts emergency diesel engine generator sets from Tier 4 regulations and requires Tier 2 and 3 compliance accordingly. (Emergency standby is defined as those engine generators that only operate when normal power is lost.) However, if the engine generator is used to support the load when normal power is present, it will be required to comply with Tier 4. This includes applications such as peak shaving and operating during storm conditions. Additionally, many state and local municipalities have more stringent regulations. It’s important to note that systems commissioning is calculated toward yearly emission allowances and may account for a large percentage of it, if not all. When this happens, there may be a fine or other legal repercussions. For more information, visit

— Paul Schlattman and Robert W. Weber

EPA Non-Road Mobile Diesel Engine Compliance Table

HP ekW** 2009 2010 2011 2012 2013 2014 2015
>3000 >2000 Tier 1 Tier 1 Tier 4* Tier 4* Tier 4* Tier 4 Tier 4
752 - 2999 500 - 2000 Tier 2 Tie 2 Tier 4* Tier 4* Tier 4* Tier 4 Tier 4
174 - 751 125 - 450 Tier 3 Tier 3 Tier 4* Tier 4* Tier 4* Tier 4 Tier 4
75 - 173   Tier 3 Tier 3 Tier 3 Tier 4* Tier 4* Tier 4* Tier 4
*Tier 4 Interim (Not full Tier 4 requirement)
**eKW is the output electric KW rating of the engine generator set, not the KW rating as it relates to horsepower. eKW may vary by manufacturer.


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What Tier 4 Emissions Rules For Backup Generators Mean

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  posted on 10/5/2009   Article Use Policy