HVAC equipment room in vented attic

A homeowner replacing attic insulation and an HVAC system asked how to handle equipment that would otherwise sit in a vented attic, where summer temperatures can top 130°F. Rather than leave the furnace, air handler, and evaporator coil exposed to that heat, the homeowner plans to build a small insulated equipment room inside the attic, sealed off with its own air barrier, and bury the new ductwork in insulation on the attic floor as current building code allows. The main questions were whether to insulate under the equipment room floor and whether the room needs a connection to the house's conditioned air.

Building science experts responding to the post said insulating below the equipment room floor is fine, including using it for sound deadening, as long as the room itself stays conditioned (kept at a controlled temperature and humidity). They noted that connecting the equipment room's air to the rest of the house isn't strictly necessary, as long as the room is conditioned some other way. The homeowner suggested a simple option: a small insulated pipe linking the room to the house, placed away from the equipment itself.

One expert also raised a separate issue: equipment noise. He recommended vibration isolators, springs or pads that keep the furnace or air handler from transmitting noise through the floor into the house, along with flexible duct connections. For anyone building a similar space to protect HVAC equipment from attic heat, insulation alone won't quiet things down as much as isolating the equipment mechanically.