To achieve today’s acceptable level of energy efficiency in your home, duct sealing has to be a priority. A blanket assumption can be made about most residential ductwork: It leaks. This is partly because cost-cutting was the main priority when home ducts were fabricated and installed in the past and partly because the concealed location of ductwork inside walls, the attic or crawl space means ducts typically don’t receive much attention or routine maintenance. The result? A minimum average of 20 percent of conditioned air produced by your HVAC system never gets to the living spaces it’s supposed to heat or cool.
In some older homes the situation is more extreme than average with duct leakage as high as 75 percent of conditioned air, along with an equivalent amount of wasted money in high utility costs. For installed ductwork in existing homes, the goal in most localities is to reduce duct leakage to below 15 percent of total duct airflow.
Paying More for Less Comfort
Homes with leaky ductwork suffer from inconsistent heating and cooling in living spaces. Frequently, rooms located farthest from the system air handler/blower don’t receive their share of conditioned air because it escapes through duct leakage long before it arrives at those rooms. These are usually rooms that are chronically stubborn to heat and cool without any other obvious explanation. Adjusting the thermostat to compensate for heat loss or cooling loss to these underserved rooms not only raises operating costs, but it also makes other areas of the home overly hot or cool.
The Balance of Efficiency
Duct leaks disturb the neutral air balance vital not only for maximum efficiency and comfort, but for healthy air quality, too. Leaks in the supply ducts result in a depressurized house that pulls cold or hot outdoor air in through structural gaps and cracks to equalize the pressure. This unconditioned incoming air competes with the furnace or air conditioner, raising energy costs. It also may originate from areas like the crawl space or attic and introduce contaminants into the breathing air of living spaces.
When leakage occurs in return ducts, the house may be overpressurized. This pushes expensive conditioned air of the house through small openings and also forces humid indoor air into spaces such as wall voids, the attic and elsewhere. The continuous flow of water vapor into these spaces can spawn the growth of mold, forming a hidden reservoir of toxic contamination that can continuously infect the household.
Inspect and Test
Because much of the span of ductwork is inaccessible to the average homeowner, a full inspection by a qualified HVAC professional is required prior to any duct sealing to accurately determine the extent of leakage as well as pinpoint the location of leaks. A proper inspection includes a pressure testing procedure that forces a fixed amount of air into the ductwork, then utilizes computer technology to calculate the exact amount of leakage expressed as a percentage of total airflow. In addition, artificial smoke may be injected into the pressurized ducts to reveal the location of hidden leaks or those too small to be visually evident.
The duct sealing process begins with cutting out any segments that may be rusted or corroded beyond repair and splicing in replacement segments. In addition, these sealing measures are standard:
- Any segments that have become totally disconnected are reconnected and mechanically fastened.
- Joints between duct segments are sealed with mastic and/or foil backed tape. All joints will then be mechanically fastened with sheet metal screws.
- Collapsed sections of flexible ductwork are restored.
- Uninsulated segments of ductwork that pass through unconditioned zones like the attic or crawl space will be insulated to a level of R-5.
- In spans where the number of pinhole leaks are too numerous to repair individually, the HVAC contractor may suggest injecting an aerosol sealant into the ducts to coat interior surfaces and resolve leakage.
For more advice on duct sealing and a professional inspection and pressure test for your Nashville home, contact the HVAC professionals at Ray & Son Heating & Air Conditioning.
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