Changes coming to temperature compensation requirements

February 2, 2025 By     0 Comments

Occasionally, I get to put on my weights-and-measures hat. Today is one of those times, courtesy of the National Institute of Standards and Technology (NIST) and the National Conference of Weights and Measures (NCWM).

You are likely familiar with temperature compensation (TC) for propane deliveries by bobtail truck. That same requirement will come to propane dispensers in about a year.

The revised requirements are:

  • Delivery trucks with meters rated greater than 20 gallons per minute (gpm) must have temperature compensation. This requirement is not a change; they have been doing this for many years.
  • Dispensers with meters rated at 20 gpm or less installed after Jan. 1, 2026, must have temperature compensation.
  • All metered sales must have temperature compensation by Jan. 1, 2030. There will be no grandfathering in after that time, depending on comments below.

The change is in NIST Handbook 130, section 2.21.2. Check with your state’s weights and measures office to see how this revision applies in your state. Your state’s adoption may modify the requirement.
The intent behind this change is probably to make the cost per Btu of energy the same at all temperatures in the name of fairness.

Here, I’m limiting my discussion to nominal 20-pound cylinders.

In pre-overfill prevention device (OPD) cylinders filled by weight (no meters), temperature compensation was automatic. Indeed, any cylinder filled by weight is automatically compensated. You could put 20 pounds of propane into the cylinder at any temperature. It would fill to 80 percent at 40 degrees F and about 85.3 percent at 80 degrees. The OPD changed that. Instead, the OPD stops the filling at 80 percent, no matter the temperature. You can’t put 20 pounds into that cylinder at 80 degrees. The OPD stops the filling at about 18.7 pounds. That’s because a “gallon” with the same number of Btus is bigger at 80 degrees.

The cost to fill an empty propane cylinder with a non-TC meter to 80 percent full is $16.67, assuming $3.50 a gallon and 40 degrees. The meter will show 4.76 gallons. Increase the temperature to 80 degrees and fill to 80 percent, where the OPD will stop the flow, and the meter will still show 4.76 gallons, and the cost will still be $16.67. However, the customer received only 93.7 percent of the Btus of the fill at 40 degrees.

Using a TC meter makes it even more complicated. Meters are normalized to 60 degrees by NIST Handbook 44, 3.32, S.2.8. The fixed maximum liquid level gauge – and thus the OPD – is set to fill the stated weight capacity at 80 percent when the product is 40 degrees (NFPA 58-2024 section 7.4.3.2(A)). This means that the grill cylinder is filled to 80 percent with “smaller gallons” since a gallon at 40 degrees is slightly smaller in volume than a gallon at 60 degrees but with the same number of Btus. Fill the cylinder to “full” at 40 degrees, and the TC meter will show 4.91 gallons. Fill it at 8 degrees, and that meter will show 4.60 gallons. The prices will be $17.18 and $16.10, respectively. The customer will pay about a dollar less for the fill at the higher temperature but will pay the same amount per Btu.

Note that mass-flow meters automatically compensate for temperature.

TC meters cost more than non-TC meters. I’m not one to discourage meter use, but you may decide that filling tanks by weight is better, especially if you don’t have enough business to justify a more expensive meter.

I’ll share one example of pricing one model from one supplier. I won’t say the brand, model or supplier. These are parts prices only and may not include all parts required.

  • A 1-in. non-TC meter is $4,323.
  • Adding a mechanical TC to that meter is $1,940.
  • The same model meter with mechanical TC included is $5,823.

Richard Fredenburg is an LP gas engineer at the North Carolina Department of Agriculture and Consumer Services, Standards Division. He is also a member of NFPA’s Technical Committee on LP Gases. Contact him at richard.fredenburg@ncagr.gov or 984-236-4752.


NOTE: The opinions and viewpoints expressed herein are solely the author’s and should in no way be interpreted as those of LP Gas magazine or any of its staff members.

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