A short answer, followed by the source guide and related questions.
Measured data comes from an observation or instrument. Modelled data is produced by a method using inputs and assumptions. Record both the method and status.
This answer is taken from Carbon Evidence Questions | Inzonex. Use the full guide for scope, assumptions and cited sources.
Use measured surface area, temperature and operating hours to calculate heat loss from boilers, kilns, heat exchangers, valves and pipework. Inzonex supplies removable modular insulation for equipment that requires maintenance access.
Do not add a calculated reduction to an emissions report until the reporting boundary, factor, implementation date and verification method have been approved.