Duct Sealing and Air Sealing
The First Step to Healthy Air and a Comfortable Home.
By: Phil Smith of www.appleblossom.biz

Houses today are built with air handling systems and many of our older homes have been retrofitted with these same air handling systems. The modern heating, ventilation and cooling (HVAC) system is designed to be a closed system. In theory the room air in the home is filtered and sent via the return air duct to the mechanism that heats or cools the air. After treatment the air is distributed throughout the house via the supply ducts. In theory little energy is required to keep the temperature constant as the air is only slightly below or above room temperature when is recycled. When the room temperature reaches the setting of the thermostat, the system turns off the heating or cooling mechanism and when it’s safe, the air handler or blower is turned off. After the air is chilled or heated to a point, the thermostat kicks in and the process repeats.

Were it not for leaks in the duct work and the air handler itself, this system would work quite well. It is important to note that without question, duct work leaks. Air leaks through seams in the duct work, through places where supply ducts -- both hard and flexible – join the main distribution ducts and where the supply duct boots penetrate floors and ceilings. Even correctly sealed duct systems leak some air. No getting around it, duct systems leak.

It is easy to see how leaking duct work results in energy loss, but why is leaking duct work so detrimental to air quality? Here is why. The air lost through the leaking duct system is, in a manner of speaking, as if it were pumped out. This pumping of air out of our homes creates a negative pressure in our homes. This negative pressure is responsible for much of the air infiltration in our homes. Just as water is indiscriminate about where it escapes your garden hose, air under a negative pressure is indiscriminate about where air is sucked in from. The available sources are the walls, doors and windows; the crawl space; or the attic space. When we feel air coming through cracks and leaks in the perimeter of our homes, we have been told to seal those cracks and leaks to prevent the ambient outside air from coming in. But with the air handler’s need to replace the air being lost through leakage, the outside air is not stopped by sealing the obvious sources; it is merely re-directed to other entry points.

Strange as it may seem, the devices designed to heat and cool our homes are pumping an average of approximately 25% of the conditioned air out and drawing in ambient air in to replace the wasted conditioned air. The systems as they are constructed, sized and installed not only allow for unacceptable energy waste, but also account for and cause unacceptable contaminants in the air we breathe. Succinctly said the system is wasteful and contributes to serious health problems. When your HVAC unit needs replacing, make sure that your service company air and duct seals and tests your home prior to sizing your unit. Duct sealed, air sealed and homes with appropriate insulation correctly installed, will reduce the mechanical requirements for your home.

Home energy experts such as Advanced Energy in Raleigh, N.C., (www.advancedenergy.org) and Southface in Boone, N.C. ‘conservatively’ estimate nearly 100% of homes over 15 years old in the U.S.A. are inadequately duct and air sealed -- in many instances with much older homes, they are not sealed at all. Given the “low price” nature of condo construction, we have no reason to think condos and town homes are any less leaky. Duct and Air sealing is the number one priority for energy efficiency measures.

The Vicious Circle of Energy Loss and Lower Air Quality
We know anecdotally that the more extreme the ambient air temperature, the harder your HVAC system has to work to heat or cool your home. Of course, you might say. But do you realize that as your HVAC unit works harder to heat and cool your home, it is also working harder to draw in more ambient air to counter the efforts to heat or cool? Here’s how. As more air is forced into the duct system increasing the air pressure, more air escapes outside the home, creating more negative pressure in your home. This negative pressure pulls in more extreme-temperature air into the home causing the average temperature in the house to drop more than the normal drop.

In the winter do you ever wonder why the more your unit runs, the colder seems inside? As the inside air temperature drops, the air is cycled through the HVAC system to be warmed to a greater degree. This in turn causes the HVAC system to work even harder to reach the thermostat setting. In other words, the more your HVAC runs, the more it needs to run due to the need to replace the lost air due to duct leaking. As you read this does it seem like we are going in circles? Don’t change the channel. We are going in circles. It’s the vicious circle of conditioned air loss.

Conversely, the less frequently the HVAC system runs the less air leaked into crawl space or attic and therefore the less negative pressure. A lower negative pressure sucks less ambient air into the house. The four basic steps below tell you how to break the vicious circle and have your currently over-sized unit run less frequently. If you get your unit replaced with a more efficient unit, it may be more economical to have that correctly sized unit run continuously. Like a small engine in your car, it costs less to run at low rpm than it does to start and stop repeatedly. The gas guzzling V8s burn more gas regardless of what they are doing if they are running. So it is with your HVAC.

Basic Steps to Break the Vicious Circle of Energy Loss and Lower Air Quality
Conventional homes built approximately 15 years ago are candidates for retrofit energy saving measures. While each home is different, all conventional homes have similar fundamental characteristics. Even though a house is comfortable (could be due to the HVAC system being sized to overcome design deficiencies and construction methods that allow energy waste) all older conventional homes are guilty of wasting energy. The first part of this paper educates the reader in the fundamental design flaw of the modern heating and cooling system as it interacts with the design characteristics of the conventional home.

Budget restraints prevent many homeowners from performing the full range of energy efficient actions. The following basic steps are affordable and have a reasonable return on investment time frame. The biggest hurdle that the homeowner has to overcome is learning what to do or finding a contractor who knows what to do and how to do it.

The Four Basic Steps

1. Seal the duct system, which includes the air hander itself, The return ducts, the supply ducts, the duct boots, and the duct boot and return duct connections to the house as completely as possible.
   
   
2. Check for and seal by-passes from the ceiling and floor to interior walls of the house.
   
   
3. Seal all penetrations in the floors and ceilings to stop the infiltration of air laden with pollutants that are harmful to your respiratory system. You may need an energy auditor or experienced energy efficiency contractor to identify these penetrations. We have seen or noticed these penetrations for so long, we don’t realize they are there or we may not know how to access them.
   
   
4. Bring your insulation up to US Department of Energy standards, not local code which may be behind current USDOE standards.
1. Insulate your home with insulation and insulating methods that have high R-value per square inch and provide maximum air sealing qualities. You may have to educate yourself as to which insulations provide better air sealing qualities and which methods are suitable and cost effective for retrofit installations.


It is well known that insulation holds heat in but how and in what way does inadequate insulation contribute to the vicious circle of heat loss. The answer really is quite simple when you think about it. The better insulated the house is, the less heat will be lost from it. The right insulation helps break the vicious circle of air loss while saving energy, money and helping maintain good air quality.

Fire treated and recycled cellulose is a popular insulation source and for good reason. Recycled cellulose is no more dangerous than household dust and is especially suited for retrofit applications -- economical, versatile, fire safety-proven and not unhealthy when breathed. Just as inadequate insulation contributes to heat loss, appropriate insulation properly installed helps break the vicious circle of heat and energy loss.

Here is something that you won’t learn on the Energy Star web site or in available USDOE documents: The USDOE requires cellulose insulation to be used on all Weatherization Assistance Program homes. Why this well kept secret? The answer is not known but huge amounts of money are given by the manufacturers of a particular type of insulation and this would be detrimental to their business. Money doesn’t talk, it swears.
2. Seal your walls from excessive air penetration. Not only homes without wall insulation but also homes built before wrapping the home with an air impervious material became standard construction practice are candidates for retrofitted dense-packed cellulose. Glass fiber insulation installed in the vast majority of homes does not provide air sealing qualities.
3. In homes with spacious attics accessed by walk-up stairs where budget constraints are not a consideration, consider going to a non-vented attic using cellulose insulation on the underside of the roof. A sealed crawl space is another option for this homeowner.

Other energy saving and healthy air options
There are many more options that will increase the ability of your home to be energy efficient. Some are economical and should be seriously considered. Some can be independently added when funds and budgets allow. And some may be critical for reasons of health. The following list should be considered after the basic steps have been taken. Of course if the following options are exercised when the basic steps are taken, there likely will be savings over doing these things separately.

Air quality measures are listed here as well as energy conservation measures. More information and explanation of the health aspects of leaking ducts and the duct system as well follow these lists.

1. Do something about your windows
   1. Install storm windows on older windows that do not have insulated glass.
   2. Or replace drafty and energy inefficient windows with energy efficient ones
   3. Temporarily install plastic film over your windows on the inside.
      
      
2. Handle the quality of air you are breathing
   1. Install affordable specialized filters that filter out volatile organic compounds or VOCs as they are commonly referred to by the EPA and other institutions concerned with air quality. VOCs come from household cleaners, carpets, anti-stain treatment, glues and resins used in furniture manufacturing and the process of making the materials furniture is made from.
   2. Have your ducts vacuumed and sanitized by a duct cleaning specialist.
   3. Install ultra violet light in your air handler to kill mold spores before they are blown in your breathing space.
      
      
3. Install a properly sized, induced fresh air system.
   Filtered, pre-conditioned fresh air induced into the HVAC system will virtually eliminate negative pressure in your home. A slightly positive pressure holds the ambient, unfiltered air outside your home. In some instances this is the only viable solution to the leaking-duct caused negative pressure.
   
   
4. Seal the moisture out of your home and prevent mold growth.
   1. Install a vapor barrier on the ground in your crawl space. An effective vapor barrier is 6 mil polyethylene turned up on the foundation wall. Seal the seams and at the foundation walls with mastic.
   2. I finances are not a deterrent, have your crawl space professionally sealed and insulated. Eliminate the insulation on the floor to eliminate breading places for mold and allow some of the floor heat to heat the crawl space. This is by far the best procedure if space and conditions allow. Sealing the duct work in the crawl space is unnecessary as the crawl space becomes part of the conditioned space envelop. In some cases opening a register into the crawl space is advisable. A professional can advise you of these matters.

We breathe unhealthy air
Unsealed duct work both wastes energy and creates a health hazard in the home. We can readily see how leaking ductwork wastes energy but how can leaking duct work create a health hazard. How can that be? We once believed our doors, windows and accompanying cracks to be the sole source of hot and cold air entering our homes and we have educated ourselves to seal these sources of air. Air coming in through the floor and ceiling was more indirect and not as easily detected.

We just did not know the air handling unit is pulling air from our crawl space and our attic. We did not realize that mole spores, damp and dirty air from the crawl space and dust mites, mineral fibers and dirty air from the attic was being drawn in and mixed with the air in our homes. This sheds light on what the EPA has been saying for years. Respiratory problems and allergies are leading health care concerns in America today.

For years home energy experts have been concerned about lost energy through these leaks. It is time to stop the energy waste and correct a health issue in our homes.

Retrofit duct sealing and air sealing is not an easy correction to make. First there has to be a commitment to clean air and to energy conservation. Energy savings alone often will not justify the expense of duct sealing and air sealing and appropriate insulation correctly installed, however, when comfort and health are factored in, many are seeing the financial benefits. The only financial return on a trip to the doctor’s office goes to the doctor.

Respiratory health hazards are not seen immediately. It took time to discover that asbestos was causing lung cancer. When you put a frog in a pan of cold water and turn the heat on, the frog doesn’t know he is being boiled until it is too late. And so it is with breathing unhealthy air.

What can you do?
If you are not comfortable doing the work yourself, there are qualified energy efficiency contractors who have the training and experience to do the job correctly. Experienced and trained contractors not only know how to make your home energy efficient but also know the dangers of over sealing, i.e., tightening a home beyond its ability to breathe. Your home has to breathe; you just want it to breathe fresh air. Ask a contractor if he has a blower door before you contract with him to do any energy efficiency work. He may not need it to do the work, but if he does not have one, he likely has not been trained properly in duct and air sealing technology. Induced fresh air may be required to help your system function optimally. If your contractor does not do this he can recommend an HVAC contractor who does.

Most homes can be air sealed, duct sealed and correctly insulated for about $1.50/sq. ft. of foot print or ground floor space -- newer homes for much less. Our older homes can be much more difficult and expensive to make energy efficient. Fortunately, these homes are often the easiest to quantify savings and justify the expenditure and get the greatest benefits.

It’s your choice – pay for air sealing and duct sealing and get a return on investment for as long as you own your home or pay for the treatment of respiratory and allergy ailments with no return on investment. We think it’s a ‘no-brainer.

Are you afraid of the cost or do you worry that you cannot afford to “do it all?” Programs are opening up to help with low cost or interest free loans. With reputable contractors consultation is free and they can make priority and do-it-yourself recommendations.

Apple Blossom Insulators -- An Energy Efficiency Contractor
We stand for a healthy environment with every person living in a comfortable home – conserving our energy, saving your money. We have been making existing homes energy efficient for over 15 years. Our portfolio of successful retrofit energy savings projects includes some homes 100 years old and older.

We partner with government agencies, energy companies and private businesses to impact the energy efficiency of existing homes. Our business is centered in the retrofit market.