How to Perform Fuel Flow to Load or Gross Heat Rate Checks

Learn how to perform a quarterly stack flow-to-load (F/L) or gross heat rate (GHR) check on your fuel flow monitor.

What are Fuel Flow-to-Load (F/L) Ratio Tests and Gross Heat Rate Evaluation (GHR) Checks?

Under Appendix D of the 40 CFR Part 75 regulations, the United States Environmental Protection Agency (EPA) requires facilities to conduct periodic accuracy testing as part of ongoing quality assurance (QA) activities. Included in these ongoing requirements are quarterly fuel flowmeter accuracy tests, such as Fuel Flow-to-Load (F/L) and Gross Heat Rate Evaluation (GHR) checks, which are interchangeable.


A flow-to-load ratio test of a flow monitor is a data analysis that is typically performed automatically by the data acquisition system (DAS). The purpose of F/L ratios and GHR checks are to ensure that fuel flow monitors have maintained their accuracy between schedules relative accuracy test audits (RATAs).


How to Perform a Flow-to-Load (F/L) or Gross Heat Rate (GHR) Check

Perform  F/L and GHR tests, according to Per 40 CFR Appendix D, as follows:


  • Calculate the hourly ratio of the stack gas flow rate to unit load for a segment of the quarterly flow rate data (i.e., those hours where the load was within 10% of the average load during the last normal load flow RATA).
  • These hourly ratios are then compared against a “reference” flow-to-load ratio, which is the average reference method flow rate ratio to the average unit load from the last normal-load RATA.
  • Alternatively, operators may perform data analysis based on the “gross heat rate,” which is the ratio of heat input rate to unit load, rather than using the flow-to-load ratio.


If there is a shift or decrease in the performance of a flow monitor, the result would be reflected in the hourly F/L ratios and would lead to an investigation of the flow monitor itself. Automatically update results of the quarterly checks to the EPA in the quarterly emissions file. The EPA may also require Abbreviated Flow-to-Load checks after corrective actions in response to instrumental malfunctions (review Section 3 of the Part 75 Emissions Monitoring Policy Manual for more information).


How Can StackVision Help You Perform Flow-to-Load (F/L) or Gross Heat Rate (GHR) Checks?

StackVision™ makes organizing your quarterly QA activities easy. First, configure the fuel flow or gross heat input parameters through StackVision’s configuration editor, StackStudio. Then, either perform your F/L or GHR check manually or as a configured sequence in ProcessNow.


Once you have performed the tests, StackVision allows you to review the data reports with ease. All you have to do is select “Stack Flow Monitoring” under QA and Certification in the Tools tab on StackVision’s Main Menu. The Flow/Load tab will be the default view. You can then select your parameter of interest and click the “Retrieve” button to display all of the data results associated with the previous and current F/L test.


We are happy to answer questions or provide more information. Contact us to learn more about StackVision.

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