Industry observers have warned that the new Part L of the Building Regulations could make it impossible for building control officers to pass schemes with standard air-conditioning systems.

The regulation, which finally came into force this week, may make it impossible for schemes with fan coil systems, which use fans to blow air over pipes containing hot or cooled water, to comply with Part L, even though they are extremely common.

Nick Cullen, a partner at engineer Hoare Lea, said it was likely that this was an inadvertent result of the Part L revision.

He said: "Assuming you are doing the calculations in the proper manner it is very difficult to get compliance using fan coils.

"I don't think that was what the government intended."

He added: "Perhaps it's time we moved on from fan coils, but the ODPM should make it explicit."

The problem is probably due to bugs in the software needed to calculate compliance with Part L of the regulations.

Observers have complained bitterly that the ODPM has not given the industry long enough to adjust to the regulations. The final approved document was only published three weeks ago.

Experts have also told Building that it remains easy to get approval for all-glass buildings even though these were expected to be phased out by Part L.