Find Tonnage on AHU | HVAC Equipment Nomenclature - How do I find out the tonnage on an AHU (Air Handling Unit)? The label/tag has faded all I have on file is the model number and the serial number, make.

Question Posted By Francisco the Building Engineer on May 3, 2011

Refer to the manufacturer’s website for their HVAC nomenclature of the model number and serial numbers and how those numbers correspond to the tonnage and other technical data. Or you can call your local dealer for the manufacturer and they will tell you.

Find Tonnage on AHU | Equipment Nomenclature

If you use the website route then be prepared to decipher the model number from the HVAC nomenclature chart which the HVAC manufacturer probably has in PDF format for download. An example of a nomenclature chart for HVAC equipment is below:

Find Tonnage on AHU - Equipment Nomenclature

Find Tonnage on AHU | Equipment Nomenclature

In your case, you will want to see number 5 for your reference if you had this type of HVAC equipment which correlates to Unit Size in MBtuh. HVAC Nomenclature charts are not only available for HVAC equipment but also some HVAC components such as compressors, motors, and other HVAC components.  These nomenclature charts are used extensively in engineering including HVAC and science to decipher lists and sometimes to keep things simple and orderly even though the layman may not see it that way.

The origin of the word goes back to the Roman days where a steward commonly referred to as a nomenclator has a system of naming and would maintain a catalog of political names so it is most likely completely derived in Latin.

Find Tonnage on AHU | Equipment Nomenclature - Conclusion

There are some pieces of HVAC equipment that may not or will not have any nomenclature type model numbers attached to the air handler or the HVAC equipment. These are usually modular units that are assembled on the job site and typically apply to large air handlers and other types of modular equipment that are very large and field assembled. To find the tonnage information along with other pertinent HVAC data finds the final stamped set of drawings for the job.

The final stamped set of drawings are stamped by the design engineer who is supposed to be a P.E. or a licensed Professional Engineer.  If you look at the schedule usually in “M” drawings for mechanical you should be able to find the equipment as installed by the mechanical contractor and approved by the engineer.


One other way to determine the size of the equipment if you can find all the drawings and paperwork for the job is to find the TABBs report. Sometimes the equipment size and sizing calculations are noted in the TABBs report. In the TABBs report you can also go by the airflow amount and divide by 400 E.G. an air handler that has a capacity for 1200 CFMs is a 3 ton unit.

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Find Tonnage on AHU - Equipment Nomenclature