This particular question is asked more often than one might think.  The first aspect of a proper answer would be to ask “at what temperature are you and other occupants normally comfortable at?”  Recommended temperatures where energy conservation is concerned is 68 degrees in the winter and 78 degrees in the summer.  Once a comfortable temperature is agreed upon you should not raise the thermostat setting more than 5 degrees above the normal setting during a typical work day absence.  If you turn the system off or raise the thermostat setting higher than 5 degrees the system will generally run longer in the evening to catch up than it would have during the day to maintain the setting. If you move the setting up or down because you might be a little too hot or cool you lose all advantages.  Try to have cool water available when the need to cool down is apparent.  Here is the USA we tend to drink too little water and warm deep tissue temperatures are the first thing that happens with a lack of hydration. 

If we talk about a safe home where furnishings or the structure begin to suffer damage then we are talking temperatures above 85 degrees and below 60 degrees.  Temperature effects are more likely to cause damage from contraction and expansion at the extreme temperatures above.  Maintaining humidity levels within the range of 55% at the high-end and 35% on the low-end is very important to the comfort of the occupants and the furnishings.  High humidity levels can cause mold growth, corrosion, swelling or glue deterioration in construction materials or furniture.  Low humidity levels are not common is our location but can cause construction materials and wood to shrink, split, crack or warp.  Regardless of the indoor temperature, direct sunlight properties (UV) can cause fading of fabric, flooring and painted surfaces.  Low E windows, window film or solar shades can reduce UV damage by about 90%.

As a side note, dust mites (their wastes) cause a majority of allergic and asthmatic symptoms in children and teens. The little critters are everywhere.  Homes that maintain a relative humidity of 50% or less are homes without dust mites.  Their bodies can’t tolerate low humidity and they dry up and go away.

If you have consistently warm or cold temperatures during extreme weather events your dwelling might not maintain the desired setting.  When this happens do not set the thermostat to a higher or lower setting.  Raising or lowering the setting will not make the temperature rise or fall faster.  You can lose track of overriding the temperature, forget to correct the higher or lower setting and ultimately pay higher bills.  Our homes are designed to meet average high and or low temperatures in specific locations.  In our region (Austin Texas) and the surrounding area, homes are designed to maintain indoor temperatures of 75 degrees with an ambient (outdoor) temperature of 100 degrees.  If the temperature reaches 105 degrees outdoors the best we can hope for is about 78 to 83 degrees indoors.   Why don’t we design for the worst case weather?  Extended cases of hot weather such as we had during the drought years (2010 thru 2014) generally don’t happen but one of every seven years or so.  If your cooling system runs about 2,200 hours a year over two thirds of the time is during part load (cooler during the evening, overnight and early morning) so sizing for extreme weather doesn’t make sense.   In essence if you designed for the worst case weather your utility bill could run up to half again as high each year (hot or not) and indoor comfort will suffer as a system too large for a home will leave humidity behind.  You will wind up with a higher bill and an uncomfortable home.