DIY: Ducts

Prepare a detailed design for your system, determining the necessary sizes for your ducts, furnace and air conditioner. Consider carefully the best location for fan units and boilers and make sure your system complies with all necessary building codes and regulations before starting work.

Draw up a schematic that shows all the components of your system. Ensure all the details are noted here, including the size of your ducts and the number and size of the holes that need to be drilled in floors and ceilings for installation. It is worth taking the time to double-check this before you begin drilling and installing. It is much harder and messier to make alterations at later stages.

Mark out the locations for all drilling to take place. Make sure supply locations in the walls are fitted to allow for curtains or other hangings. Drilling into the floors must be between the floor joists and not directly above them. Details of all drilling needed will be on your plans; an example is included in the references below.

Put your furnace or central air conditioning unit into place. When fixing, ensure that plenty of space is left for all the ducting and air return fittings that will be needed. At this stage you will also fit the plenum, the large duct positioned on top of your central unit.

Install the ducting itself, measuring and checking each section before fitting it. Metal ducting is most common, but there is flexible ducting available if that is preferred. If using the flexible ducting you must avoid bending lengths too sharply as this may damage them or obstruct air flow through the system.

Finish by installing all grilles and remaining registers. This will be done after any paintwork, plastering or other decorating has been completed.