Improving the efficiency of your HVAC unit
Duct leakage is a real problem within the industry with little comprehension by many contractors. The smallest of leaks can truly impact the efficiency of any HVAC unit impacting customer’s bottom dollar. Since 2006 when Energy Star Homes started specifying a duct leakage threshold there has been some general improvements however overall the issue of prevention is still not being addressed by many contractors as it should. Even in the best of homes with varying price levels the results can be quite disappointing.
Acceptable Air Leakage Levels
The requirement for acceptable air leakage is no more than 6 cfm/sf; however most homes far surpass this recommendation demonstrating much greater air loss via leaks. Homeowner’s are often in the dark about the loss of dollars escaping from their air systems, and too often contractors don’t want to take accountability for ensuring that all steps are taken to provide their customers with not just a finished product, but the best finished product that will support their customer’s comfort and long term financial needs.
Effective HVAC Installation Methods
Steps should be taken to ensure that duct systems are not only functional but also efficient. One of the most effective installation methods is to seal all register boots to drywall or subfloor as the duct enters the living space. In difficult cases, infrared scan devices can be utilized to locate leaks behind the drywall. This specialization comes at a cost but in some instances the upfront cost may be worth it when evaluating long term savings.
Duct Leaks between Floors and Framing Cavities
It has come to be known that floor and wall cavities are not entirely in the thermal envelope, thought to be the pressure boundary of the structure. Although not obvious during construction duct leaks that occur between floors or framing cavities can easily make its way out of the thermal envelope to the exterior of the structure. LEED for Homes Green Raters and Home Energy Rating Systems (HERS) testers report that during whole house blower door testing in which floor cavities are also analyzed, as much as 50% of pressure is identified outside the cavity.
Open Web Trusses pose Disadvantage to Homeowners
The results are baffling particularly during these economic times where no one can afford to be throwing money away. Open web floor trusses only worsen this situation. Since there is no compartmentalization within a truss floor system, an envelope leak in one location of the building can easily be measured on the opposite side of the structure. Open web trusses offer many advantages for ductwork installation; however it is easily comprehensible why they also pose a great disadvantage to the customer.
Factors to consider in Ductwork Design and Layout
Many of the schematics encountered represent duct systems without actual duct component dimensions. It is the responsibility of the installer to understand:
- The design of the structure
- The customer’s desires for comfort
- Constraints for:
All of these items will impact ductwork design and layout. This is not an easy task, and most certainly not something in which you want an unqualified inexperienced installer becoming involved. Most often than not I am called in to evaluate poorly functioning systems and find myself explaining to customers that poor design and layout is the root cause for their problems. When ductwork systems are crammed into tight spaces inaccessibility results in seams and connections getting missed.