EHH week 08: HVAC precon

This house will be heated (and sometimes cooled) by air running through ducts out to each of the rooms and back from some of the rooms.  There are actually quite a lot of ducts in this house, and the trick is routing them through the structure so they stay hidden above the ceiling or inside the walls.  Easier said than done.

Anticipating this common design problem, VELOCIPEDE made a 3D model of all the ducts to assure there was a viable route from central mechanical room to perimeter windows.  Then once the main floor was framed, the architect, mechanical engineer, general contractor, and HVAC contractor spent a couple hours at the site spotting the route of each and every duct.

This on-site planning effort is called a “precon” for preconstruction meeting.  We considered not just the ducts, but also the plumbing pipe routes, structural obstacles, and architectural niceties like centering grilles below windows.  There were (as there always are) a few problems that we had to work out in the precon.  For example, we had to change four 8” ducts serving the great room to three 9” ducts to better fit in the available joist bays.

Then we marked the chosen routes and grille locations right on the structure for the subcontractor to follow at install.  A couple hours of planning effort should avoid problems and make things go smoothly later on.  Remarkably, duct layout is usually left to the installers to figure out the day they arrive on site with a truckload of ducts and fittings.