How important is it to have a humidifier around a piano that is in a New York apartment with steam heat?

Susan, Humidity is vital for a valuable piano; but a good piano tuner can install a humidifying system to piano itself. I pour a quart or so of water into a plastic tube system and it moistens the piano interior. System plugs into regular wall socket; on the piano is a little light that blinks when system needs refilling. And a plastic watering can w. the right size spout and mouth is included. I use this only in winter since the summers are so damp.

Any competent tuner will know about the device.

Much Much easier than the free-standing humidifiers. I use one in my bedrooom at night and have to clean the parts w. bleach once/week due to bacteria build-up. A nuisance, but my sinuses feel better. You could also try pans of water on radiators in living room.