ASHRAE Guideline 14-2014 (updated as 14-2023) is the standard complementary to IPMVP that defines the detailed statistical thresholds (R-squared, CV(RMSE), NMBE) for M&V baseline models, and is the absolute reference in case of contractual dispute.

ASHRAE 14 is a normative US standard that is also widely used internationally. It provides formal definitions of M&V metrics, calibration thresholds at monthly and hourly resolution, uncertainty calculation methods, and sampling and instrumentation procedures. The full document costs around USD 250 from ANSI but a public preview is available. The combination of IPMVP (method) and ASHRAE 14 (numerical thresholds) forms the complete M&V reference framework.

Quote the ASHRAE thresholds verbatim in the M&V Plan — paraphrasing them is a common source of post-hoc disagreement.