Forced Air Ductwork Routed In Attic

This article describes heating and air conditioning ducts that have been placed in or beneath concrete floor slabs.

Forced air ductwork routed in attic.

Forced air systems are usually the cheapest ones to install in homes today and a furnace qualifies as this type of system. With hundreds of square feet of ductwork surface area in the attic and a δt of 75 f the air coming out of the vents in your home will be significantly higher than 55 f. Hvac air ducts located inside concrete slab floors invite a surprisingly broad range of building problems that fall into two broad categories. Verify that ducts outside the conditioned zone are properly sealed.

Unfortunately this practice is all too common in our northern cold climate putting air conditioning ducts in the hottest possible place in the house during the summer and putting heating ductwork through the coldest possible part of the house in the winter. Since most homes have their hvac system serve multiple functions at once it can be cheaper to install the unit in the attic because the roof access can make inspections maintenance and repairs at lot easier. Turbine vents usually depressurize the attic sufficiently to pull conditioned air up through the air leaky ceiling into the attic which increases the cooling energy use. Flexible duct work must be stretched tightly for maximum air flow.

Hvac ductwork in floor slabs. Throw duct leakage into the mix and the problems are even worse. Keep as much of the ductwork span as possible inside the conditioned envelope of the home. Never locate ducts at the end of the trunk line run.

Last take off run to be located 12 18 from end. Functional troubles such as lack of air flow or collapsed ductwork and environmental problems such as. Heat pumps and ducts are part of it too. Use insulated duct or duct board in unheated spaces.

If your ductwork is breaking down under the slab a coating is not going to do you. Ducts that are in a ceiling tend to be a little more effective in distributing cooled air throughout a room. Where ductwork must be routed through unconditioned zones that experience temperature extremes such as the attic crawl space or basement reduce thermal loss by insulating affected spans. When you put the ducts in an unconditioned attic and have the minimum insulation allowed you want to move the air at a higher velocity pushing it up near the maximum recommended by acca manual d 900 feet per minute fpm for supply ducts and 700 fpm for return ducts.

In warm climates it is common practice to run heating and air conditioning ducting through attic spaces simply because it is easy to do. Always stagger take off ducts by 12 to maintain pressure.