Phil wrote:

Hi. I am in the process of completing a home-brew central heating
controller which will be able to measure the temperature outside of the
house as well as in 3 rooms inside.

Our house faces north/south and I plan to mount the outside sensor just
under the eaves but do I mount it on the northerly side or the
southerly?

Obviously, the northerly side never sees the sun but I am concerned that
the sensor may be affected by stored heat, or should that be cold so,
has anyone got any advice please?

Keep in mind that even if you place the sensor on a north-facing
wall, between the Spring and Autumn equinoxes the sun rises and sets
north of east and west respectively, and between those times the
sensor might give falsely-warm readings through being in the sun.
Probably not an issue in full summer, but you can get really cold
nights/days in March and April, and perhaps early May.

One of my garden fences faces north, and I had to place a temperature
sensor on it where the morning sun can't shine on it, by hiding it
behind a fence post. Evening sun isn't an issue as it sets here in
summer at about 4:30pm due to 70' high trees on the ridge-line at the
back of the house.
--
Terry Fields