Air Conditioning Repair (Ductwork to replace or not to replace that is the question)

Q Is it time to replace my 40-year-old ductwork? Can reduced heating and cooling costs justify the high cost of replacing the ducts, or will sealing and insulating the existing ducts be just as effective?


A There is not a simple yes-or-no answer to your question. Improving your ductwork will no doubt improve the efficiency of your heating, ventilation and air conditioning (HVAC) system, although it might be difficult to justify the cost of a complete replacement. Depending on the specifics of your home, your future heating and cooling dollars might be stretched further by first addressing other components.

Consider the keystone of green building: the whole-systems approach to designing, constructing and operating a home. For example, ductwork is just one of many components of your home's heating and cooling system, which also includes:

• roofing

• shading

• insulation

• air infiltration sealing

• windows

• furnace

• air conditioner

A light-colored roof transfers less heat to the attic. Awnings and roof overhangs above south-facing windows can block direct heat gain from summer sun. Tight ductwork means that heated or cooled air isn't lost to the attic or crawl space. The list goes on, and all measures impact the amount of energy needed to heat or cool a home.

Most people have a limited budget for energy efficiency improvements. To determine the smartest way to spend your dollars, first evaluate the unique aspects of your home by having a professional energy audit performed. Professional raters called Home Energy Rating System providers offer this service and can be found on any of these Web sites: www.calcerts.com, www.cheers.org or www.cbpca.org.
If you don't have the budget for a professional audit (usually $300-$500), complete PG&E's free online energy audit at www.pge.com/myhome/saveenergymoney/analyzer.

Often, an audit will show it is most strategic to focus on efficiency improvements that do not require destruction - and expensive reinstallation - of finishes. For example, it might be more cost effective to install attic insulation and seal and insulate accessible ducts before tearing up finishes and replacing all of the ducts.

However, health and comfort concerns might override cost considerations. If the existing duct insulation is asbestos and is crumbly and potentially introducing dust into adjacent leaky ducts, there's strong reason to replace the insulation - if not all of the ductwork. If some rooms are overheated and others are under-heated, the system might have been poorly designed and would provide additional incentive to replace it.

If you opt to replace the HVAC system, ensure that your contractor performs calculations to optimally design the ductwork and size the furnace and air conditioner based on the size of your home, level of insulation, types and locations of windows and other relevant elements. Build It Green's Green Building Guidelines (www.builditgreen.org/guidelines) offer additional best practices, and the Air Conditioning Contractors of America (www.acca.org) provides a contractor locator and calculation manuals to ensure appropriate system design. Finally, PG&E offers home cooling and heating fact sheets at www.pge.com.