Ductwork insulation

Choosing the best ductwork insulation for a home.

Ductwork is the system of pipes and ducts which circulate heated or cooled air all over the house. Addition of insulation to ductwork lowers energy consumption, utility bills and gives a more comfortable home. There are many types of ductwork insulation that include; fiberglass ducts, metal ducts, ventilation ducts and lastly fabric ducts. The standard type of ductwork is fiberglass. However, a newer reflectix duct wrap is also being used lately. It is however that before ductwork insulation addition, always check for leaks first and seal them. HVAC contractors usually use mastic material to seal leaks because it doesn’t shrink or deteriorate from the joints. The proper way to use mastic material is to rub it on the ducts and leave it to dry correctly, for say, a day.  Notably, duct tape should never be used to seal ductwork despite its name. It decomposes and decomposes and deteriorates with time. When that happens, it doesn’t seal leaks anymore hence leaving useless, sticky ductwork.

Fiberglass insulation

Rolled Batts
Fiber thermal insulation for houses and facades textured background

Fiberglass is the most prevalent type of ductwork insulation because it is easy to install, cost-effective, and absorbs noise. Also fiberglass insulation is easy to replace since it’s common to find in most hardware shops. It’s important to always inspect it for any moisture absorption. Reflectix, on the other hand, is lightweight and doesn’t readily absorb moisture like fiberglass. Also, it is very stable and efficient and hence an excellent type to use too. When installed according to specifications of the manufacturer, reflectix duct wrap has an R-value of 5.6 (highest R-value is 8). Similarly, it has foil faces on the outer part which hold bubble packs between layers of polyethylene.

Importance of ductwork insulation

Ductwork insulation warrants that the air circulating through the duct system maintains the desired temperature and doesn’t ‘leak’ out. In case of leaked air, it leads to unnecessary energy loss, and that means the HVAC system will work harder. Ductwork leads to wasted energy which is not suitable for people and the environment. Poor ductwork insulation could lead to a loss of 10-30% of the overall energy that is used to heat/cool a home. Therefore proper ductwork insulation prevents energy wastage, temperature drops, leaks, and condensation build-up.

The necessity of ductwork insulation

Ducts are made of thin material like sheet metal or fiberglass, which makes it easy for the air moving through them to be lost. Appropriate insulation ensures that regulated temperature of this air is maintained as it comes from the furnace/ air conditioner to the entire house. Unconditioned areas such as floors, ceilings, and basements require more ductwork insulation compared to the rest of the building.

Insulation versus condensation

Every time fresh air passes through warm areas, it causes condensation in the ductwork.  Consequently, this condensation causes moisture build up in the enclosed space of the duct system which causes all sorts of problems like mildew growth and mold.  It is, therefore, necessary to install proper levels of insulation that prevent condensation in your ductwork and avoid mold and mildew growth.

Unconditioned ducts

Attic Crawl Space
Inside gable and joist view of ongoing project, insulation of attic with fiberglass cold barrier and reflective heat barrier between the attic joists

Unconditioned space is the area in the outermost shell of the house and is not heated or cooled. It is the area outside the thermal envelope. Such areas include attics, crawl spaces and garages, and basements. Insulating ducts in the basement makes it colder. To remedy this, the ducts and basement walls should be equally insulated. Also, a well-sealed vapor barrier should be put in place on the outside of the insulation on cooling ducts to avoid moisture condensation.

Why not use unconditioned ducts

Unconditioned ducts are considered the worst places to put ducts. Here are ways to reduce duct losses; remove the ducts out of the attic and put them into the conditioned space. This leads to zero additional loads. Also, one can encapsulate the attic, which is equivalent to putting them in a conditioned space. It leads to extra duct load, but it’s better than having them in the unconditioned attic space.  Another way is to hide ducts deeply in insulation. In humid climates, however, burying ducts is a risky strategy. Likewise, you can replace the duct system with ductless mini-split heat pumps. The last way is to take a hydronic distribution and keep pipes inside conditioned space. Water can be used instead of air to move heat out or into the conditioned space.

Heat loss via duct walls is inevitable. This heat is much needed, especially during winter, otherwise why the heating system? Therefore to remedy heat loss, effective thermal insulation is a necessity. It also reduces the cost of utility bills and improves energy efficiency.