Any stay of 7 nights or LESS, is charged HKs .. housekeeping credits. The number of HKs are based on size of unit. Usually, you get enough HKs yearly IF you book full week stays ... else, when booking a stay and you do NOT have enough HKs in your account you have to BUY MORE HKs at the booking time. The Member Directory has a chart showing the HKs needed for each size unit per 1 day-7 day stays: ST(28 hk), 1BDR (63HKs), 2BDR (77HKs) and 3BDR (140HKs).
I believe, it is $2.25 per HK to buy. If a reservation is made with HKs that you had to buy, no refund of the fees for buying those HKs.
You get 1HK for each 1,000 points held in your Member ID.