You need to review the specifications of the items you calibrate, and assure your calibration laboratory (room) area is environmentally controlled to the spec for the unit(s) with the tightest environmental requirement. If you are doing relatively low accuracy electrical calibrations, the requirements may not be that tight. Some examples of tighter specs I have seen are as narrow as 23 Deg C +/- 1 Deg C with no greater than 1 Deg change per hour and %RH 45% RH +/- 5% RH. That is for a higher accuracy environment. I have also seen as loose as 23 Deg C +/-5 Deg C and %RH Greater than 30 %RH and less than 60 %RH. For low accuracy electrical calibrations, your environmental requirements are likely to be closer to the second set of requirements. But you MUST review the specs of the units you actually use. Whatever the manufacturer specifies for those units is the limits you must maintain. There may be units where the manufacturer does not specify environmental limits. Electrical power plant switchboard meters, for example are designed for a very wide range of environmental conditions. The calibrator you use, however, may have much tighter limits. Review all of the items, and spec to meet the tightest one.