HMP Glenochil's 20 million Harviestoun Hall opened in 2005 to replace three old buildings.
But Scotland's chief inspector of prisons, Dr Andrew McLellan, said in a report published today that soaring temperatures inside the new 244-cell complex made conditions "unbearable" for both staff and inmates.
The watchdog said sweltering conditions during the summer saw prison officers having to install portable fans to help keep the landings of the block cool.
Individual inmates have also had smaller fans placed in their cells.
Dr McLellan said about Harviestoun: "The windows in the cells are large and let in lots of natural light, but they are fitted with restrictors so they will only open a few centimetres. This means that fresh air in the cells is restricted. It is unfortunate that a new building would appear to have such problems with temperature."
He recommends that the temperature in Harviestoun Hall "is kept at a level which is comfortable for prisoners and staff".
The inspector's comments are part of his latest report on Glenochil, which houses around 440 prisoners serving more than four years. There were 67 lifers at the prison at the time of the inspection in October last year.
Dr McLellan highlighted a number of other problems with the new block. He said Harviestoun's sheer size made it difficult for officers to see everything, and also to avoid shouting. The inspector also found that long-term prisoners were angry at having to share cells in the new block. Some inmates were found to prefer staying in old cells in an existing hall rather than share in Harviestoun.
Dr McLellan called on the prison's managers to review the need for long-term prisoners to share cells.
The quality of food at Glenochil also came in for criticism from the inspection team.
Budgeted costs of food per inmate have not changed in more than a decade, Dr McLellan said, remaining at the 1.57 per person per day set in 1996. He noted that the rising cost of potatoes in particular was having an impact on the quality and quantity of what was being served up.
Fruit and vegetables are provided to inmates, but the availability falls far short of the recommended five portions per day, the inspector said.
However, staff and inmates at Glenochil were praised for coping with the long phase of building work. Prisoners told inspectors they consistently felt safe at the jail and that relationships between staff and prisoners are good.
Dr McLellan added: "Glenochil is already very much changed and there is more change to come."
The Scottish Prison Service (SPS) said Glenochil management was exploring ways of improving ventilation in Harviestoun. A new kitchen area was also being planned for the prison.
An SPS spokesman said: "We welcome this report and were delighted to see [Dr McLellan] commented favourably on some of the recent developments at the prison."
Margaret Mitchell, justice spokeswoman for the Scottish Conservatives, said there was "no excuse" for the ventilation problem inside the new building. She added: The inspector is right to bring this up, but I would also like him to highlight more worrying aspects of prison life such as the availability of drugs and mobile phones."
New hall to increase spaces for inmates as jails redeveloped
A SECOND prison hall costing more than 20 million will open at Glenochil jail next month.
Abercrombie Hall will provide places for 254 prisoners and will increase the jail's design capacity from the current 440.
A further 8 million is being spent on a health centre and 7 million on a new staff and visitors' complex.
The work is the latest stage in a massive development programme in Scottish jails costing more than 120 million.
Polmont Young Offenders Institution, as well as Perth and Edinburgh jails, is also undergoing complete redevelopment, providing what the prison service calls "fit for purpose" accommodation.
The service has proposed closing Peterhead jail, which is the only prison in Scotland where inmates have no access to in-cell sanitation.
A consultation on the future of Peterhead prison has been carried out, but any decision will be dependent on funds being available pending the Scottish Executive's next spending review later this year.