2 Chronicles 29:17

Now they began on the first day of the first month A happy beginning of the new year! Thus should every year begin with a reformation of what is amiss, and the purging away of all the defilements contracted the foregoing year. In the sixteenth day they made an end

Cleansing the house, and porch, and courts, and all the chambers belonging to the temple, in sixteen days. This is mentioned to signify, partly the universal abuse and defilement of all the parts of it by Ahaz, to remove which so much time was required; and partly the diligence of the priests in this work.