Distribution boxes facilitate ductwork in limited spaces.
The space available for ventilation systems can often be limited and accommodating multiple ducts into a small space without the need for structural changes can be challenging.
If you do not have the needed room for segments and fittings available, you can use a distribution box. A distribution box allows you to distribute air from one duct to several, or in extract air systems, to collect air from several ducts into one.
MagiCAD includes both generic and product-specific distribution boxes for ventilation systems.