Conditioned Attic Ventilation

If there is no hvac in the attic why not just air seal and insulate at the attic level much easier and less expensive.

Conditioned attic ventilation.

In cold climates attic ventilation is a common method to remove humid air. The loss of energy efficiency means some designers choose to move the ductwork into the conditioned areas of the home and leave the attics unvented. In cold climates the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow and to vent moisture that moves from the conditioned space to the attic ventilation acts to bypass the vapour barrier created by most roof membranes. A vapor retarder is recommended in cold climates.

When the hvac system is located in a vented attic it is exposed to extremes of hot and cold. The energy needed for air conditioning and heating typically goes up 10 when ducts are in the attic ueno 2003. Creating a conditioned attic without a hvac unit in the attic. Seems to me the only reason to create a conditioned attic is to bring the hvac system and ductwork into the thermal envelope of the home.

Poorly insulated ducting can cause heat loss in colder months and the loss of conditioned air in the summer in vented attics. In some cases a conditioned attic assembly may be desired where scissor trusses make it difficult to insulate the floor or in cathedral ceilings where the intent is to turn the attic into living space. At first it may seem odd to add insulation for warmth and then purposely allow cold air to. Attic fans are intended to cool hot attics by drawing in cooler outside air from attic vents.

Insufficient ventilation can lead to moisture problems during the winter and decreased energy efficiency during the summer but too much ventilation can be just as bad if not worse. In theory if you install a small exhaust fan in the gable wall of an unvented attic along with a passive duct or grille that allows conditioned air from the floor below to enter the attic as makeup air the humid air in the attic will be exhausted and will be replaced with less humid air from the home. A design decision to have a central ducted heating and cooling system with ducts and air handler located in the attic is another good reason to insulate and air seal at the roof line which will provide a conditioned or semi conditioned space for the hvac equipment. Just like properly sizing your furnace and air conditioning unit you want precisely the right amount of attic ventilation for your home.

Intake vents located at the lowest part of the roof under. Oversized heating and cooling units are often installed to make up for the inefficiency of leaky ducts further increasing the purchase cost and energy bills.