Vendors of small multi-user, multi-tasking automated library systems, those supporting 8 to 40 users, represent that the systems can be installed in normal office environments, but the fact is that reliable performance is achieved only if the environment is controlled. In older buildings the period between heating and cooling seasons often brings days of high temperature and humidity. Weekend shutdowns of central air conditioning as an energy conservation measure can also affect computer system performance. There are special computer room air conditioning units available for wall mounting or ceiling suspension. No ductwork is required; only a 3.5 inch diameter hole to the outside for venting. The units usually require a 15 Amp circuit. The installed cost of a unit is approximately $3,500. The most widely used units are the Sanyo models 12KL11 and 18KL12, units with 12,000 and 17,700 BTU per hour capacity respectively. Many air conditioning and electrical contractors have experience with the installation of such units because they are popular not only in small computer rooms, but also in telephone switching stations, laboratories, and studios.