Where in N. Raleigh/Wake Forest can I get an HVAC distribution box made?

[woodworker2000]

I need to get a small HVAC distribution box built so I can tie in a couple of bathroom exhaust fans into one roof penetration. Anyone know where in North Raleigh/Wake Forest area I can get this done? If none in the N. Raleigh/Wake Forest area, anyone else in the Raleigh area? I haven't checked any of the BORGs yet but do they sell any pre-made boxes? I'm thinking I need one approximately 12" cubed or smaller. If I really wanted to get fancy and reduce the possibility of backflow (see next paragraph), I suppose I could go with something more cone-shaped with the smaller end of the cone feeding into the roof penetration. Thanks in advance for any recommendations.

By the way, I know some people don't recommend tying bathroom exhaust fans into a single exhaust but I've done some research on this issue and have concluded that any backflow concerns are minimal with the configuration I am intending. I intend to have all hoses from the fans tie into one side of the box and the exit to the roof penetration tie into the opposite side. All piping from the exhaust fans to the box will be 3" diameter and the exit from the box will be 4" diameter. In addition, from the box through the roof will be a much shorter run than either of the runs from the box to the fans. Since air flow, like most/all things in nature take the path of least resistance, any "backflow" from one exhaust fan to another would have to enter the box, turn around 180 degrees, travel further back to the other exhaust fan than it would have to travel to exit the roof (through 3" diameter hose as opposed to the 4" pipe exhaust through the roof) and overcome the built-in one way flap at each exhaust fan. I just don't see this happening and believe that any exhaust air from one fan will instead flow out of the larger/shorter hose through the roof.

 

[Alan in Little Washington]

Your bathroom units should already have back-flow preventer flappers on them- to keep cold air from flowing into the bath and/or hot air from leaving. This required. Think what happens when you turn on the kitchen exhaust fan- that air must be replaced with outside air from some source - a bathroom is the least desirable place for it to happen.

How many baths will you be venting? I would just use a wye with two baths and two wyes with three baths. Although not as critical as DC system use 4 -4-6 and 6-4-6 wyes.

Something else to consider- replace the fan units with lighted grills and put a single fan in the attic. For much quieter bathroom venting I put one of those turnip-shaped axial fans in the attic. It draws from three locations- two tub/shower areas and a toilet room. I used double pole switches for the lights/fan in the three locations- turn on the switch in any location and the fan turns on, but only the light in that location turns on.