All ducts, air controllers, and filter boxes must be sealed. While the ducts of conditioned spaces do not need to be insulated, they must be sealed. It is important to note that not all air conditioning systems require sealing and insulation. So, which ducts don't need to be sealed and insulated? The answer is aluminum ducts in an attic or mezzanine, supply or return ducts located in the conditioned space, and return ducts located in a ventilated attic.
For proper ventilation of a building, windows must be opened near the top and bottom of the walls to allow warm air near the roof and cold air near the bottom. The heat transfer constant between zone A and the outside is 2 h, between zone B and the outside is 4 hr, and the extraction of surface condenser air causes a drop in condenser pressure. If the ducts remain inside the conditioned enclosure, they do not need insulation or testing, although it is necessary to seal them with airtight materials. Additionally, insulating the ducts that stay within the conditioned wrapper may still be a good idea, particularly if you live in a warm or mixed climate where cold ducts can become a dehumidifier and cause sweating.
If the ducts are behind finishing materials such as drywall, it's tempting to make the smallest openings possible in existing ceilings and walls to reduce disturbances. All joints and joints in air ducts, air treatment systems, and filter boxes are practically hermetic using tapes, putties, liquid sealants, gaskets, or other approved sealing systems. The well-sealed, low-delta P low heat pump air treatment system in the garage seems to be fine as long as all the inlets are well sealed. This notch in the ceiling beams, as shown in the photo on the left, allowed for framing of the flat roof after installation of the ducts. Fibrous glass duct plates are available with a hard and durable inner surface treatment to prevent erosion of agglomerated fiberglass; however, this type of fiberboard is very expensive.
When redirecting ducts, access them directly from the basement, mezzanine, or attic if possible. Attic supply and return ducts must be insulated with an R value not lower than R-8 for 3-inch ducts. With regard to the builder who is trying to plan out the location of the duct works for a ceiling or lattice design, Manual D contains essential information. The supply ducts of attics are insulated with a minimum of R-8 and all other ducts with a minimum of R-6 except for those located in conditioned spaces. It requires some planning but it is best practice to keep heating and cooling equipment and ducts inside the house. Ducts have temperatures close to 120°F and ventilated attics are close to outside temperatures; usually there is a temperature difference of more than 100°F.When designing heating and cooling systems it is best to use HVAC design services to calculate heating loads (calculation of heating and cooling loads from Manual J), select equipment based on performance criteria (Manual S), and design distribution of ducts so that appropriate amount of heat and air flow reaches each room (Manual D).
Fibreboard ducts are manufactured with specially designed hand tools or with grooving and sealing machines. In conclusion, aluminum ducts in an attic or mezzanine, supply or return ducts located in conditioned spaces, and return ducts located in ventilated attics do not need sealing or insulation. However, it is important to note that all other types of ducts must be sealed with airtight materials such as tapes, putties, liquid sealants, gaskets or other approved sealing systems.
