Frequently Asked Questions

What does "the house is a system" mean? How is the principle used to improve the performance of homes and businesses?

First, let's look for a moment at the way homes and buildings have traditionally been viewed by the building industry. Each trade is seen as a stand alone entity. Their work and the sub system they install are viewed separately from the other subsystems and the structure as a whole. No one is charged with integrating the parts into a correctly functioning whole.

When the first real scientific research into how structures function began, the researchers quickly noticed that everything seemed to influence or impact the performance of everything else.

Air ducts that leak in the attic caused the water heater in the basement to backdraft CO into the house. Too many recessed ceiling can fixtures caused the fireplace to not draft properly. Closing bedroom doors increased the infiltration of outside air into the home by hundreds of percent making rooms drafty and uncomfortably cold or warm. It has taken many years to learn how these seemingly unrelated things interact and how to resolve the problems.

The scientist soon realized that the whole structure interacts and that all of the so called "sub systems and parts" function in one interactive whole. They coined the phrase, "The house is a system." to describe this new understanding of the physics of homes and buildings.

Even the climate and the occupants are considered part of the system. We have learned that what are "best building practices" in Minneapolis will cause a home in Houston to rot. The building interacts with the specific local climate and to perform well it must address these climatic demands. The occupants "operate" and interact with the building system. Their needs and the way that they intend to use the home or building must be considered to ensure that the performance they want can be delivered.


I've heard differing opinions about vapor barriers/retarders. Should we use a vapor barrier/retarder in the walls of our new home or business and if so, where should it be installed?

We have all learned growing up in this business that a vapor barrier is part of a good exterior wall. The building code for decades has required one “on the warm side of the wall in winter.” They tell us that without the vapor barrier our walls will grow mold and the studs will rot from water damage due to condensation.

Building science research has shown us that this is all a matter of where you are building. It is as untrue for the humid south as it is true for a cold climate zone. The codes and most building practices that we all grew up with were developed for the North. The South has a very different climate.

The science all comes down to the Second Law of Thermo-dynamics. This law of physics tells us the direction of moisture and heat flow among other things. Up North, the dry, cool air is outside and the moist air is inside most of the year.

In the South, the conditions are exactly the opposite. Our air conditioners create dry air inside while the outside air is very humid most of the year. For this reason, our research has found that the use of a vapor barrier in the South can cause more problems than it solves. Our winter temperatures don't get cold enough to cause condensation or frost inside of our insulated walls, so this is not a problem Southerners need to be concerned with.

The recommended best practice for the South is either to build a breathable wall, one without any vapor barrier at all or to install a vapor retarder at the exterior of the studs. This makes sense if you think about it. Vapor barriers should go on the warm side of the wall. That is the outside in the South and the inside up North.

Another thing to consider is the type of wallpaper that you intend to install and where you intend to use it. A vinyl wallpaper is a vapor barrier. It should never be installed on the inside of an exterior wall in homes or buildings in a hot and humid climate zone. Many people in the south have removed vinyl wallpaper only to find big mold colonies growing behind it. Now you know why.


Are my windows really important to comfort and efficiency? What windows are the best?

Yes, the windows you select are one of the two most important components in your overall energy efficiency and comfort package! I have completed too many air conditioning and heating equipment sizing load calculations to remember. One thing that stays consistent is that the windows account for about one half of all the heat that enters or leaves a home.

That's right. The windows normally let in or out as much heat as the walls, ceilings, doors and air leaks combined! Before the mid 1990's we had storm and double pane windows, but they did little to stop heat gain in a home. Solar window films and solar shade screens could stop about one half of the heat gain but they also made the rooms dark. They worked by blocking half or more of the light along with the heat they blocked.

We now have a new type of window product called Low-E and Low-E Squared. Both products are double pane construction and use the principle of emissivity to control the flow of heat into and out of a home. The process can be "tuned" to maximize the benefits for either a heating dominated or a cooling dominated climate.

Southern Low-E or Low-E Squared as it is sometimes called, blocks the heat from the sun, but allows the light to enter the home. This allows us to have brightly-lit rooms that remain cool and comfortable. The Northern Low-E products are "tuned" to allow the sun's heat to enter the home, then stop the heat from radiating back to the outside, trapping it inside.

These glazing products have really dropped in price in recent years. Low-E windows are now code mandated across the country and are extremely cost effective in new construction or renovations. They are only a little (5%-10%) more than standard double pane windows. They can be purchased in aluminum, fiberglass, vinyl or wood frames and thermally broken frames from all major manufacturers of windows.


Is the goal of making a home healthy at odds with making a home efficient?

No, this is not at all true. This is a myth. In fact, a sustainable home by definition has all of the following performance attributes:

  • Healthy

  • Efficient

  • Durable with low maintenance

  • Safe

  • Comfortable

What we are describing is a home that performs properly. We should not and do not have to make choices between these desirable attributes in our homes and buildings. These goals can only be met by understanding the relationships that comprise the "system" that is the whole the structure. The climate in which you are building forms a part of the "system." The impacts of the occupants (also part of the "system") must be understood as they can have very significant impacts on how the building functions and what it is asked to provide.


We have family members or staff who have allergies, asthma, or chemical sensitivity and that demands that our home or business have excellent indoor air quality. How can that be efficiently done in an environment like a major American city?

The key to providing the indoor air quality that you are looking for is to control the quantity, quality, and source of the air in the facility. In new construction, we should also address source control by selecting the best materials to contribute to a healthy indoor environment. Our homes and buildings today often depend on infiltration (accidental leaks and drafts) to provide our "fresh" air and produce good indoor air quality. This is much like depending on the tooth fairy to provide for your retirement savings.

By definition, infiltration is the unplanned entry of an unknown quantity of air, of uncertain qualities, in varying amounts, from an unknown source and at irregular times. Ventilation is the planned introduction of a known amount of air, of controlled qualities, at predetermined times, from a known source. Our current codes require mechanical ventilation of all new or remodeled homes and businesses. The standard is ASHRAE Std. 62.2 for homes. There are several ways to meet this requirement and we can help to design a system right for you.

One of the best ways to solve Indoor Air Quality (IAQ) concerns is to remove or not use products that off gas VOC's or act as pollutant sinks to trap and hold pollution in the building or home. Avoiding products with particleboard components or sealing them to stop them from off gassing would be one example of this approach.


We have been given a wide range of suggested sizes for the heating and cooling system in our home or business. Everybody seems to be sure that they are right. How can we select the correct contractor and unit to provide comfort and efficiency?

Relax, there is a recognized way to be sure that the air conditioning and heating system you install will efficiently maintain comfortable temperature and humidity conditions in your home or building. The Air Conditioning Contractors of America (ACCA) represent the professional heating and cooling contractors across the country.

ACCA publishes manuals containing scientific and long tested methodologies to accurately determine the amount of heating, cooling and airflow each room in the home or business will require. The ACCA Manual J sizes equipment for homes and ACCA Manual N addresses small commercial buildings.

The best way to do this is to use one of the computer programs that are available today. These programs, when properly used, size your equipment to serve the space on the hottest or coldest day with a margin for error built in. They also tell you how much air each room will require. This information is essential to sizing the air distribution system or ducts as they are often called.


We have a problem with our air conditioning and heating system. Some rooms get too much air while others get too little. What is the problem and how can it be solved?

This is a common complaint today. The most often seen scenario is that the rooms close to the air conditioner/furnace get too much air while those further away get progressively less.

This is caused by the HVAC contractor failing to correctly design the air duct system that distributes the air among your rooms. The contractors most often use a simple slide rule type of device they call a "ductalator" or "duct calculator." Most of the time they use a ductalator intended to size for sheet metal ducts then they install flexible duct that carries about one third less air than metal ducts of the same diameter.

They often don't adjust the size to compensate for what is called the "effective length" of each duct run. The duct calculator assumes that all runs are 20 feet long and leaves it to the designer to adjust this recommended size to the true length of that run including turns and other impediments. This step is virtually never done. Therefore, we end up with the short runs being oversized while the long runs are undersized.

The solution to this comfort and efficiency problem is to use the Air Conditioning Contractors of America (ACCA) duct design methodology know as Manual D to size all air duct runs. We must then install balancing dampers on each run to allow us to fine tune the system so that each room receives +/- 10% of the airflow that the Manual J indicates it needs. In an existing situation, we may be able to correctly balance the airflow with balancing dampers and a flow hood to measure airflow from each grille. We often need to install some new duct runs to solve the comfort problems.

There may be other contributing factors too. If the grille and duct that carry the air back to the equipment are undersized, the fan will not be able to move enough air to make distant rooms comfortable. This is a very common problem. Two recently completed national field tests (US Dept. of Energy - NCI) concluded that the average system is moving less than two thirds as much air as they are designed to move. This has a direct negative impact on comfort, efficiency and delivered heating/cooling capacity to each room.

In this case, we would need to add a larger return air grille and duct to allow the system to produce its full heating/cooling capacity and airflow. This often leads to the unit producing and delivering as much as thirty percent more total capacity than it did before.

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