Most acoustic guitars are made from a natural material - wood.

Wood absorbs and gives off moisture according to its environment, making the wood expand or contract. If this happens too quickly, or the conditions are too extreme, then the guitar - especially the soundboard - can crack or distort.

Always transport the guitar in a case and allow it to come to temperature slowly in its case before taking it out. Modern hot and dry central heating can cause havoc with acoustic instruments.

More expensive "solid top" (i.e. non laminated) guitars are more at risk than cheaper instruments with plywood tops and sides.

Heat alone (e.g. direct sunlight) can cause problems on some guitars as the glue used in construction can be softened, maybe causing the bridge to lift for example.

Sunlight can also bleach or discolor the finish.

Around 45% humidity and  22deg.C is pretty much right for musical instrument storage. If you are comfortable, probably the guitar is. 

Historic collectable instrument c 1900 -1910

 Freshman Apollo 2 DCED Electro Acoustic

 Freshman Apollo 2 OCED Electro Acoustic

 Gitane GJ-15 Cigano - "Oval Hole"

 Gitane GJ-15 Cigano - "D Hole"