The 54-year-old, who does not want to be named, injured his spine and was unable to work for several weeks as a result of the incident in Woking on 17 December 2012 at a new- build head office for the World Wildlife Fund.
He was working for Wilden Services Limited, of Hemel Hempstead, which had been sub-contracted to install a ventilation system in the new building.
Guildford Crown Court heard that the fan unit, weighing some 630kg, fell over as it was being moved on a pallet truck and pinned him underneath.
Wilden Services Ltd, of Hemel Hempstead, was fined £15,000 and ordered to pay a further £7,148 in costs after pleading guilty at an earlier hearing to a breach of the Health and Safety at Work etc Act 1974.
After the hearing, HSE inspector Denis Bodger commented: “The employee was seriously injured and could have been paralysed had his spinal cord been damaged by the falling unit.
“Companies should always ensure that extreme care is taken when moving heavy items, and that includes properly assessing the risks in advance and agreeing a safe system of work.
“The incident was entirely avoidable with better planning and management.”