Why are you guessing? Just measure it! 70º is far too cold. At the dead lowest 75ºF it is quite likely with 70ºF ambients you will get RI (perhaps you know that already?) Generally 80ºF is a good target with periods as low as 75 and as high as 85ºF 18ºF or C I am guessing C 18ºF makes no sense at all. Has this changed (like when the heating got turned down at the beginnings of spring?) Often our homes (especially us in cold climates) have changes indoors dry in winter and cool in fall and spring before the heating is on all the time. This change can mean rebalancing the enclosure.