Like humidity, temperature is extremely important for your piano
Changes in temperature will affect basically the metal
structure of your instrument, and that includes the strings.
When warm strings expand and pitch goes down, when cooled strings
contract and pitch goes up, and because they are not the same
length If the piano was tuned at 76F it will go out of tune at
80F and it will also sound out of tune at 72F.
Constant changes of temperature will greatly help loosing the
tuning of the piano and will make the instrument unstable. If
this condition is maintained for long period it will even shorten
your piano life the same as humidity does. Ideally, the
temperature should be kept even all year long, between
74 oF and 78 oF.