Hello. I live in the bottom unit of a flat (two unit building) in San
Francisco, about a mile from the ocean. The top flat is kept unoccupied
most of the time so the owner, who lives in another nearby city, can make
use of it when he or one of his grown kids needs / wants to stay in SF. The
weather in the coldest parts of winter is typically in the upper 40's /
lower 50's during the day and in the upper 30's / lower 40's at night. This
winter has not been typical as it's been warmer this winter than I can ever
remember it being (except for the last couple days).

To save money, I don't turn on the heat in the flat, and will instead put on
additional clothing to stay warm which is fine with me. Thus the house for
the most part is never heated.

Somebody mentioned to me that perhaps this is not good for the house to
never be heated during the winter. There's no mold anywhere in the house
except for a little scattering of it on the two most bottom 1" aluminum
slats of the blinds at the three west-facing windows in the front of the
house (which I intend to clean off real soon) and a bit on the window sills
that those aluminum slats rest on. There's no mold on the walls or anywhere
else.

Am I damaging the house to not turn on the heat in the winter weather
conditions of San Francisco that I described? Is there any code or
standards or discussion that I could read online that covers the necessity
(or non-necessity) of heating a house in various climates to prevent damage
from mold? I do not want to do any damage to the house and will heat the
house if I am damaging it.

Thanks for any help.

Chris.