John Gillion Watson, 56, of Vicarage Court, Sleaford, will go on trial in September after he entered not guilty pleas during a hearing at Lincoln Crown Court.
The unit was evacuated with no injuries to patients or staff, but ambulances were diverted to other hospitals in Lincolnshire, as well as further afield.
Councillors have since criticised plans to further centralise services at Lincoln in light of the incident.
Watson appeared in court to face a charge of arson with intent to endanger life on March 29 and an alternative offence of arson being reckless to endanger life on the same date.
It is alleged damage of £180,000 was caused to Lincoln County Hospital.
Wearing a grey jacket and grey jogging bottoms, Watson, who was a temporary patient at the hospital, spoke to confirm his date of birth and then pleaded not guilty to the two arson charges.
Judge John Pini QC adjourned the case for a trial at Lincoln Crown Court on September 26.
The trial is expected to last several days.
Watson was remanded back into custody and will next appear at Lincoln Crown Court for a pre-trial hearing on September 5.
Judge Pini told Watson: "I am adjourning your case for trial."