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HVAC Ducts Should Not Have Holes Inside The Walls
HVAC duct planning is a difficult enough of a science, but some installations are designed to fail as 
HVAC ducts should not have holes inside the walls.
Why do I say planning duct work is a difficult science?
Because their job is to balance air flow and the indoor temperature, and that ain't easy!  Many, many factors go into designing the HVAC system for a house - sizes of rooms, open spaces, numbers of windows and doors, cubic this and that, and on and on.  Air has to evenly come and go.  It really is a design best done with computer programs.
Older homes had heating systems that blew air around with small, metal ducts.  Metal ducts are famously leaky. 
Someone got the idea to wrap some joints and such with tape - the infamous duct tape.  And it worked, basically, but only until the tape dried out and the leaking began again.
Now HVAC science uses a combination of metal ducts and flexible ducts.  Flexible ducts are nothing more than huge slinkies with plastic wrapped around them.  Some are insulated.  They can be extended and fitted and wrapped around things to send air where ever.  But it all must be tight!  ... more

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