A focal point wall is one that can be seen from across the room, it dominates the room. In a living room this might be the wall you see when entering from the front door. It might be the wall you see when coming in from the kitchen. Usually the hearth or seating group will be centered around this focal point.
Having a large painting in this position of the room will help anchor attention and focus on the main function of the room. A 30 x 40 painting (shown at right) or larger is often the standard size for a work placed over a sofa, mantle or master bed. A large foyer may also require a work of this scale.
A large room (larger than 20 feet, or with a cathedral ceiling) may require a painting larger than 30 x 40 inches. A diptych (2 or 3-panel painting) will create a large enough focal point to hold attention in the room. This helps people function more easily, as balance in the room creates balance for it's inhabitants.
I often create custom paintings in these larger sizes. Commissioned works can be 36 x 48, 48 x 60, 48 x 72, or other custom sizes.