An energy audit of a business on the Isle of Man involves recording various characteristics of the building envelope; including the walls, ceilings, floors, doors, windows, and skylights. For each of these components the area and resistance to heat flow is measured or estimated. Air leakage through the building envelope is a concern. The goal of this exercise is to quantify the building’s overall thermal mass. The audit may also assess the efficiency, physical condition, and programming of mechanical systems such as HVAC (Heating Ventilation and Air Conditioning).

Isle of Man Commercial energy audits include a written report estimating energy use given local climate criteria, thermostat settings and solar orientation. This could show energy use for a given time period, say a year, and the impact of any suggested improvements per year. The accuracy of energy estimates are calculated against billing history showing the quantities of electricity, natural gas, oil, or other energy sources consumed over a given period.

Some of the greatest effects on energy use are user behaviour, climate, and age and construction of the building. An energy audit therefore has to include interviews with certain employees to understand their patterns of use over time.

The energy history can be calibrated using local weather data in combination with the thermal energy model of the building. Advances in computer-based thermal modelling can take into account many variables affecting energy use.