Imagine walking through the house in summer and feeling a steady, silent breeze in every room, or ditching the pull chains for clean wall switches that actually match your decor. Knocking this out all at once means the mess happens once, your rooms finally match, and you can lock in a better rate from an electrician who wants a multi-room job instead of a single small fix. Late winter home improvement sales are the sweet spot for picking up the fan units themselves at a discount before the spring rush hits.
You will want to get at least three different quotes from local electricians before you buy a thing. Electricians price things differently when they see multiple rooms on the list, and having options keeps everyone honest. Once you know what the labor is going to cost, you can match it up with the price of the fans you picked out during the winter sales.
Remember that the 0% intro APR for 15 months on purchases and balance transfers is a hard deadline, not free money. If you still have a balance left when those 15 months are up, interest will kick in on what is left over.