Big house, small snake, oh boy. I wouldn't even know where to start. I guess the best I can say is to slowly take the reptile room apart. With a snake that small I would even check your racks or other enclosures in case it got into one of them. Check the normal drawers, closets, boxes, furniture, etc., and of course anything that produces heat. I wish you the best of luck, I know that will be a hard snake to find.