Is there such a thing as having a home that is too well sealed and insulated? In other words one that is “too tight?” Many moons ago, I had a customer who worked for a precast concrete company. He was in the process of building an all-concrete earth-sheltered home along the banks of the Crow River in Minnesota. Built into a cliff overlooking this tributary to the Mississippi, he was elated to tell me about the air lock entrance to the home (a vestibule with two doors, only one of which could be opened at a time) and the fact that they would not be able to burn a single candle inside as it would use too much oxygen. It certainly sounded impressive to me at the time. Yet, even before becoming attuned to healthy construction techniques, it also sounded dangerous.
Fast forward to today with many miles behind me in my energy career and I can unequivocally say, you can make your home too tight. For many folks, the next question is, “Why is this a problem? Isn’t as tight as the International Space Station (ISS) exactly what you should shoot for?” Let’s look at why “No” is the correct answer.
Think of your home as a living structure. It changes as it ages and with each season. It “exhales” as it ages too. Houses will release (exhale) volatile organic compounds from paint, carpet, furniture, wallpaper and so on. These compounds get into the air and over time will make their way outside. Eventually, this stops as the materials reach a certain age. Yet, as these materials cease releasing their chemicals, homeowners reintroduce others with cleaning, cooking, smoking and just general living. As an example, we once lived in an 1883 farmhouse in North Carolina. Obviously, the materials used in construction had long since ceased their exhalations. However, the original owner, Mr. Pinnick, smoked a pipe with cherry tobacco. Every now and then we’d catch a whiff of cherry tobacco smoke. Local legend was that Mr. Pinnick was checking on his house. Of course, it could have been that the house absorbed the smoke and was releasing it.
Modern energy efficiency practices focus on sealing the exterior of the home to minimize gaps and cracks. Further, it focuses on using highly efficient heating and cooling equipment and the best appliances in terms of their energy sipping character. Proper efficiency standards also require a certain number of air changes per hour (ACH). This slightly technical-sounding term simply means that the air inside the home should be completely replaced with air from the outside a certain number of times each hour. Generally this is handled by the HVAC equipment but leakage can also provide a substantial portion. Industry standards recommend .35 ACH for general occupancy and allow this to be obtained by mechanical and leakage means. Like the ISS, a completely sealed home will rely on 100% mechanical means to provide the necessary ACH.
So, what is the risk to sealing your home too tightly? Indoor air quality experts cite the chemicals released inside the home as one danger. Mold is another. Especially in humid climates, a tightly sealed home becomes the perfect petri dish for cultivating unhealthy levels of mold. The health effects of both can be debilitating and difficult to diagnose.
The bottom line is to allow for proper fresh air when tightening up your home. These calculations can become complex so don’t hesitate to enlist the help of a trusted contractor to be sure you get the right information. Additionally, contact your local electric cooperative to find out what other energy efficient measures you can implement in your home.