I have never taken the temp of my house in the winter, but i like to be warm, with all my aches and pains, it is a necessity really, i like feeling cosy and not having to wear heaps of layers of clothing as i find that uncomfortable, i think if it were me i would make the place a bit warmer when your parents visit and wear less clothing myself, i hate my guests to feel uncomfortable and as you get older you do seem to feel the cold more,it would be more pleasant for them, it puts me off visiting people when i feel cold,but if i know there house if going to be cooler than mine , then i will wear warmer clothing,your parents could do that too and probably do, but when you are elderly it is hard to retain the body heat.