Do a move on everyone coming out of the steam rooms then you will come to a room with people sleeping. Make sure not to run into any buckets because that will wake everyone up. In that room there is one guard and he is on the other side of that furnace lookin thingy. knock him out then walk out the door.

When you're the Hot Boiler room, don't go around the room or the person in the centre will spot you, you'll wake the fat sleepy men and you can easily knock over a Bucket. Go straight through the room towards the man in the centre, without knocking over any buckets and going on front of him. Move behind him then stun him. On your way out towards the green arrow, don't knock any buckets!