"Bubba" wrote in message

and do you actually know trader, that if all duct systems were
properly sized and installed, you would not need a closeable flap on
them. Unfortunately, most systems are installed by the lowest bidder.
Its all driven by the builder. He builds the home, hires the lowest
bidding subs and profits at the highest sale price. This process
happens in some of the least expensive and most expensive homes
around.
Bubba

But what constitutes properly sized. You may want a bedroom warm and comfy
while I like it cool to sleep. Thus the reason to have those closeable
flaps. One size does not fit all no matter who does the install.