If you must put furniture near an air duct, use a shield or guard plate to direct heat away. Frequent and sudden changes in relative humidity are especially bad. Wood is most likely to crack when the climate in a home suddenly changes from hot and humid to cool and dry. Avoid placing furniture in front of radiators, heat runs or fireplaces. Store table leaves as close as possible to the table so they adjust to the same humidity conditions.
Air can hold more moisture at a high temperature than at a low one.
Wood can best handle temperature and relative humidity changes if they occur gradually. When air conditioning your home, it is best to keep the intake of outside humid air to a minimum. Dehumidifiers need to be used during wet, rainy times and in damp rooms to remove excess moisture from the air. The ultraviolet rays of the sun will damage a finish and bleach the wood underneath. Prolonged exposure to sunlight can cause the finish to crack, sometimes in a pattern resembling the skin of an alligator.