Complex sentence: Owing to variations in humidity and likely clothing, recommendations for summer and winter may vary; one for summer is to, with that for winter being to, although by other considerations the maximum should be below--for sick building syndrome avoidance, below.
Split into simpler sentences: Owing to variations in humidity and likely clothing, recommendations for summer and winter may vary; one for summer is to, with that for winter being to. Although by other considerations the maximum should be below--for sick building syndrome avoidance, below.