Which way do you tilt venetian blinds in the winter?

This is a matter of personal choice and what one hopes to achieve.

LIGHT, VIEWS, AND VISABILITY

• Downard tilting, as seen from the inside, permits direct light from the sky to enter, but blocks the horizontal view. If the slats are the same angle as the sun, very little light will be reflected into the room, but furnishings in the direct sunlight will invariably fade.

• Acute angled upward tilting prevents most sunlight from entering. The horizontal view will also be totally blocked.

• Horizontally positioned slats can bring reflected light into the room, the sunlight or light from the sky reflecting off the horizontal surfaces of the slats, sending light upwards, and in all directions. A horizontal view to the outside will be possible through the slats, but, if privacy is desired, it may be worth noting that people passing nearby may be able to look directly into the room.
  

WARMTH
If there are radiators under the blinds, attention may need to be paid to their position in relation to hot air flows from the heating units. Downward slanting may channel hot air out from the room and into the window area, whereas upward slanting will retain more of the warm air circulation within the room.

APPEARANCE
Of course, if the venetian blinds have just one attractive surface, many would tilt the blinds so that the attractive surface is innermost to some degree. In most cases this would mean tilting them downwards, with the upper surfaces facing the room.

SAFETY/SECURITY/PRIVACY
If you have Windows that are on the bottom floor or have Windows that can be seen by neighbors... tilt the blinds so that anyone who may try to peak in will only see the ceiling. This direction is very useful for any time of the year anyway.