Step 1: A Trombe wall is a passive solar heating system.
Step 2: It consists of a thick heat storage wall, usually made of concrete or masonry, placed behind glazing.
Step 3: Solar radiation passes through the glazing and heats the wall.
Step 4: The space between glazing and concrete wall allows heat collection and air movement.
Step 5: In Trombe wall arrangement, this distance is generally:
\[
10\text{ to }20\ \text{cm}
\]
\[
\boxed{10\text{ to }20\ \text{cm}}
\]