Have been in some cold crawlspaces and utility rooms during these hot days. This double reflective attic insulation is clean, easy to install and very effective.
Here is the ideal installation to preserve conditioned air throughout your house. All the outgoing ducts are insulated so no cool or warm air is wasted in the utility room or inside the walls. After construction is complete your only option is to cover the exposed outgoing ducts in the basement or crawlspace. This will save some money and prevent condensate from dripping on your air handler and deterioration of your metal duct work. Seal seams with foil tape.
For attics, if you don't already have insulation on the ceiling, and you want to treat it as an indoor space, just staple it to the rafters and seal with foil tape. Click on image for link.