Using science and technology to measure home performance.

How many miles per gallon does your home get? While it's relatively easy to obtain an efficiency rating for an automobile these days, it seems rather impossible to get a good grasp on exactly how efficient your house is. Just as there are guidelines to evaluating the mpg of a vehicle, there is an approved process for evaluating the efficiency of a building. This process has been labeled as the "Home Energy Rating System," or HERS rating. By taking into account all things that determine the efficiency of a building, a certified HERS rater can easily determine how well your home performs, as well as how your home will benefit from improvements.

Using high-tech software, proposed improvements are modeled to determine exactly how much energy will be saved. This quantitative method puts an end to guessing about where you should spend home improvement dollars. The system not only illustrates where a homeowner may get the most "bang-for-the-buck," but it is also recognized by the mortgage industry. The HERS rating is so accurate that the mortgage industry will actually loan you more money if it is used to make cost-effective improvements to your home; up to fifteen percent of a home's appraised value is available for every home that is bought or refinanced!

Surprisingly enough, the things that have the greatest effect on a home's performance are most often invisible to the naked eye. Professional building diagnostic tools are essential to the HERS rating. Without them, an accurate examination of a home is impossible. The blower door, duct blaster, manometer, and infrared camera are the backbone of the rating system.

A blower door is a large fan that is used to depressurize the home by forcing air out. When combined with a manometer (a device that measures pressure differences), a blower door provides an accurate measurement of how "leaky" your house is. The leak factor is one of the main components of energy modeling because the more leaky the home, the less efficient it is. The more "air-changes-per-hour" that your house undergoes, the more it costs you to reheat the new air that has replaced the old. If you could pay to heat your indoor air only once, and keep it inside the home, then you would undoubtedly be much happier when you receive your monthly utility bill .

What are most often overlooked are the pathways that air takes within the walls of your home. These interior chaseways and soffits typically contribute as much to inefficiency as would a door that was left open all winter long. These airways are easily documented with a blower door and proper use of pressure gauges.

The ductblaster is very similar to the blower door, yet smaller. This tool, as the name suggests, is used to measure the leakiness of ductwork. As with the leakiness of the walls, the more holes that are in your ductwork, the less efficient it is. Leaky ductwork is a bad scenario for a number of reasons. Let's begin with the efficiency side of the Coin. Think of ductwork as a large vacuum that pulls air from one place and sends it to another. Air is either blown out of a supply duct or sucked into a return duct.

On the supply side, conditioned air is lost to the attic, crawlspace, or unfinished basement. This not only heats an unconditioned area, but it also depressurizes your living space. The depressurization causes air to enter the house to replace the air that was lost due to leakage. This replacement air is not "fresh" air, as it is often considered, but originates from your crawlspace, basement, attic, or the worst-case scenario, the flue pipe of a combustion appliance.

On the return-side of a system, the holes pull in air from the attic, crawlspace, or basement (most of which are unconditioned), and distribute it to the rest of your home via your ductwork. This introduction of cold air (wintertime) not only makes for an inefficient system, but it can create serious air quality problems. Most of us would not want to breathe the air found within our crawlspace, but that's essentially what we're doing if the air handler is on and we have leaky ducts. As you can tell, duct leakage can certainly affect the efficiency and overall health of a home. Therefore, it is one of the main factors within the HERS rating.

With all of these thoughts about tightening a home, the question is often asked, "Is it possible to create a house that is too. tight?" This is the most frequently asked question of a rater. As we have discovered, in order to have an efficient house, the house must be tight. But, shouldn't there be a little fresh air? Yes, there should be fresh air. But there should befresh air. Not air that originates from the dank, moldy crawlspaces ... not air that enters through the cracks in the wall where the critters live ... not air that comes from the attic that is filled with fiberglass insulation and old snake skins. The fresh air should truly be fresh. It should be introduced into the home through a mechanical system. This enables the homeowner to control when they get fresh air (often on a times'), how much fresh air they get (maybe a little more on poker night), and it enables the control of where the fresh air is delivered (to every room with a supply duct). By tightening the house and. introducing fresh air mechanically, it is possible to create an efficient home that also has healthy indoor air quality.

Perhaps the most fascinating tool used by HERS raters is the infrared camera. This high-tech device allows the viewer to see the relative temperature of surfaces. This enables one to see how well their insulation is performing, or if it's even there to begin with! When combined with the use of a blower door (and a temperature differential between inside and outside), the infrared camera allows the rater to locate the holes in the building envelope. When the cold outside air comes in to replace the air being pulled out of the house by the blower door, the surfaces around the holes are cooled, and therefore are easily identified. This allows the homeowner to see exactly where their heating dollars are escaping their home!

As the cost of fuel rises and indoor environmental quality becomes more important to families across the nation, people are realizing the benefits of home performance. raters have begun to fill the need for home inspections that reflect the principles of building-science. A typical home performance evaluation includes an energy modeling of your home, a list of cost-effective improvements (focusing on efficiency, health, and comfort), guidance through the Energy Efficient Mortgage process, and most importantly, insight into how home performance actually works.

Isaac Savage is President of Home Energy Partners, Inc., a home performance retrofit company, based in NC. He can be reached at 828-359-1155 of [e-mail]