Is it inside or is it outside? Is the perfect climate for what's inside reflected in what is happening outside? Probably not. Pianos are very delicate, hand made instruments made from wood and metal. They are not supposed to get wet or even damp. If the normal air in the house is extremely dry, there might be a need for a humidifying system. If there's too much humidity in the air, a dehumidifying system might be in order.

There are also practical measures to take that don't take extra money, nor prep work or installations. First, make sure that the piano is away from any drafts or possible drafts, like windows and forced air vents. Don't put the piano so that it will be hit by sunlight coming through windows. The piano should always be in the 'shade' of the room.

Another practical step is to prevent drastic decreases or increases in temperature, from hot to cold or cold to hot. If nothing else, the piano will surely go out of tune if subject to substantial shifts in temperatures over a short period of time. Let the room adjust to new temperatures gradually, as gradually as possible.

More: Living in Climate: Wet and Muggy? Dry and Windy? From One Extreme to the Next?
Also: Tips for Taking Care of Your Piano