Boy, that is one question I get asked a lot.
Howard Miller used to say every year, and now it’s every two year. Some companies said “Ask a repair man”, We were given a grandmother clock when we got married years ago, and that owners manual said it was lubricated at the factory and “no further lubrication is necessary”. Yeah. It’s like saying they put in oil in your car when it was made, so no oil changes are necessary.
I tell people around 5 years if you have a fairly dust free home. If you live next to construction site, do woodworking with out dust collection, remodel or refinish your floors, have a cigar, deep fat fry, etc. I would consider getting it done much more frequently. If it’s not good for your lungs, it’s not good for your clock.
I mean, if you got your transmission fluid changed weekly, your tranny should last for ever. However, you could have given a lot of your friends new transmissions for what you spent on fluid changes.
You will need to ask your self what works best for you. Most modern grandfather clock movements range between $400-$1000 (except tubular bell, which costs a little less then our transmission example), and then you add the cost of labor, shipping and taxes, so in some respect, it is a cost analysis.
So there you have it. To protect my clocks I keep all of myy woodworking stuff is in the garage, and when we refinished our floors, I put the clocks behind closed doors and under rain coats.