How much air is your house leaking? Are you unknowingly slurping in dirty air from your garage and attic? Perhaps a blower door test can help you find out. Tom White is the Publisher of Home Energy (aka "my boss"). He's gotten to know a lot about home performance in this job over the last few years. He knows about blower doors and pressure envelopes, duct blasters and thermal envelopes; and has been initiated into the knowledge that you never use duct tape on ducts. But there was one more initiation to go. So he went to the Web to find someone to do an energy audit on his house.

"I went to the ServiceMagic Web site that I learned about editing a Home Energy article," says Tom. "Within less than a minute after I entered some basic information about my house and what I was looking for in the way of an energy audit, the phone rang." It was Sustainable Spaces, a home performance contractor located in San Francisco. Tom made an appointment for his audit for the next week. "They were offering a 'Stimulus Special' for $395."

The house Tom shares with his partner Dmitri was built in 1907. "The home has never been remodeled," says Tom. "We recently had the furnace replaced with a hot water radiant system. We have been careful to keep to the original features of the home, so we got our radiators from buildings built around the same time that used to be part of the heating systems in buildings at Fort Baker." They also installed a renewable energy source. "We installed photovoltaic (PV) panels on our roof, but we should have had the audit first to show us how to use less energy and save on the PV.  Our annual true-up statement says we owe $75 for electricity, but I want to get that down to $0!"

Rob Mitchell, an experienced contractor who knows a lot about Bay Area houses, came with two younger men for an audit of Tom and Dmitri's 102-year-old home. The crew closed all the exterior doors and windows, installed a "blower door" in the main doorframe, and depressurized the house. Immediately, dust and insulation particles began to pour through the "pocket doors" from the attic. After taking some measurements to get a general sense of how leaky the house is, and blocking some of the major air leaks, the crew from Sustainable Spaces then pressurized the house. "We walked around the house with a liquid pencil, which showed there is airflow around switch plates, gaps in the baseboard where the home is connected to the outside, and the cabinet in our kitchen where there used to be 'torpedo tubes,' which used to hold hot water heated by the wood stove, and other places" says Tom.

So the old house has some problems with air leakage, which means heating energy being lost to the outside. The crew also found out that the humidity in the kitchen was 20% higher than that on the outside of the house. "We both took showers that morning, and I had a cup of hot tea," says Tom. That was enough to keep the humidity high a few hours later.

Since the home has no mechanical ventilation, moisture build up could lead to mold growth on surfaces in the living spaces, or-even worse because it is hidden-within the walls. Mold can degrade building materials and create poor indoor air quality. Tom has allergies and a moldy house could make it difficult for him to breathe. Since Tom is living in the mild climate of the Bay Area, where we can open windows and get fresh air other ways in our leaky houses, the moisture may not hang around long enough to be a problem. If he lived in a cold climate such as Minnesota's, or a hot-humid climate such as Atlanta's, fixing the air leaks in his house without adding mechanical ventilation could create a "sick house", meaning one with poor indoor air quality due to mold.

"We won't get the report until next week," says Tom. The report will include specific numbers for air leakage from the house to the outside-or in this case between the living spaces and the attic and basement. Too much air flow means lost energy and too little means a sick house. The report will also give a range of measures that will make Tom and Dmitri's house healthier and more energy efficient. "We'll decide what measures we want done when we get the report. We made our heating system more efficient with the radiant system that heats the living spaces and provides us with hot water. We use half the gas now to heat water than we did before. So spending a lot more on fixing the building envelope doesn't make so much sense to us right now. We'll probably fix the big leaks by air sealing around the attic. And we may insulate under the floor between the living spaces and the basement."

"I wanted to have our house audited mostly because I'm curious," says Tom. "And we want to save energy." But from now on when Tom talks about home performance, and the importance of healthy and efficient homes, it will take on a whole new dimension-the homeowner's perspective.

Blower door equipment is used to measure a home's
air leaks. A blower door test is part of the evaluation for
determining a home's HERS Index.
Photo by: D&R International

Remember the day when most men knew the horsepower of their muscle cars? Now most of us are concerned about miles per gallon. But what can we use to bring prestige to our houses? It used to be that a large square footage gave us bragging rights. But if all goes according to the plan of the Residential Energy Services Network (RESNET), the talk around the water cooler will be "What's your house's HERS score?"

Home energy ratings have been around since 1981. The idea began in the mortgage industry to credit the energy efficiency of homes towards the home mortgage. An energy efficient home means that the homeowner is spending less each month on electricity and natural gas and therefore has more to spend on the mortgage. RESNET has been developing the Home Energy Rating System (HERS) since 1981. In the beginning, it was the higher the HERS score the better. But because of the more widespread introduction of renewable energy systems, such as photovoltaics (PV) and solar hot water systems, into homes, and the ability of many houses today to produce as much electricity and/or hot water as they need over the course of a year-these are called net zero-energy houses-a HERS Index of "0″ is the goal. A HERS score of 85 means that a new home meets Energy Star standards. A HERS score of 150 means you're living with an Energy Hog. The typical existing home in the United States has a HERS Index of 130.

HERS raters look at a home's heating and cooling efficiency, insulation levels, appliance and lighting energy use, window efficiency, a home's solar orientation, and other factors that are tailored to the home's climate region, and use computer software to calculate a HERS index.

Some readers my be asking, "Why should I care?" You should care because the HERS score is becoming the standard du jour for homebuilders. If you want a bigger, energy efficiency mortgage, you'll need a HERS rater to measure the efficiency of the home you want to buy and to tell you what retrofits you need to do to qualify. If you are a builder and want to catch the "green wave" by earning an Energy Star rating for the new homes you are selling, you've got to get those homes rated by a certified HERS rater.

Many states have Energy Efficiency Portfolio Standards and Energy Efficiency Credit trading, and many more will in the future as we move towards national standards for meeting greenhouse gas emissions goals. The HERS Index is in place to serve the need for a third-party verifier of energy efficiency improvements.

Want energy efficiency tax credits for your new home? Better find a RESNET-certified rater. Moving to Canada? The Canadian RESNET, or CRESNET, is in the process of accepting the U.S. standards. I don't know the HERS Index of my home, but we did recently have some air sealing and insulation work done-but not quite to Energy Star standards. My guess is we'd score about 100. What's your HERS score?