Hi,
i had an HVAC system retro-fitted in my home. The installer left some
of the work undone..such as not installing a humidifier on one unit and
failing to cover the duct openings (the part that run to the rooms).

Can someone point me to a site or documentation on how to install the
grills on these openings? Are they screwed into the sheet rock or into
the duct itself somehow? Is there anything special i need to be aware
of when adding these grill covers?

Also, are register sizes standardized? Meaning, am i likely to find
the grill covers at home depot that will fit the registers?

thanks much