Green construction comes with many different approaches but one of the fundamental issues is building with energy conservation as the cornerstone. So you spend lots of money building an energy efficient house; but do you really know if it’s energy efficient? The best way to test your home for energy efficiency is to perform a blower door test.
The blower door test is used to test a house to determine how airtight it is. The airtightness of a house is a very good indicator of how efficient a houses thermal envelope is. You can have great insulation in the walls but if there are leaks around power outlets, doors, windows and utility penetrations then the air leakage can offset the great insulation.
The blower door test is very simple to perform for a qualified technician. The photo shows a standard blower door test apparatus installed in an exterior doorway. A blower door test apparatus includes three components. The components consist of a canvas door panel, a calibrated fan, and a device to measure fan flow and building pressure.
The calibrated fan is temporarily sealed into the exterior doorway using the canvas door panel. When the fan is turned on it creates a small pressure difference between inside and outside of the house. The pressure difference between the inside and outside of the house will cause air to leak through any holes in the building envelope. The tighter the building is, the less air that’s needed from the fan to create a change in building pressure.
The results from a blower door test can be used to calculate an HERS rating which is used to certify home for the Energy Star program. The blower door test results are used in conjunction with inspections of the homes insulation installation and design values from the plans to calculate the HERS rating. The lower the HERS rating the more energy efficient a home is. A rating of 100 is considered the average home while a rating of 0 indicates a net zero home.
The really nice thing about this test is you can walk around to suspect areas (windows, doors, openings) and look for drafts by using a simple smoke device. You can easily see drafts at these locations and determine corrective actions. I’ve witnessed several of these tests and it’s amazing to see areas that you wouldn’t even think of during construction. The one area that really amazed me was a interior pocket door between a bedroom and bathroom. If you know how pocket door frames are built then you know that inside the cavity for the door it’s open to the space above within the wall framing. If you have an un-insulated area above that pocket door and you subject the house to an uneven pressure you’ll quickly see where the smoke goes!
Even if you have an old house this test can be quite beneficial. You can perform the same tests using the smoke tracer to identify leaks in the building envelope. These leaks can then be sealed to improve the airtightness of the house. Many states and public utilities even offer these types of services for free in order to improve energy efficiencies in their areas.
Excellent summary, Todd.
LEED for Homes addresses this issue in it's Energy & Atmosphere section. One interesting fact that we learned in building our home is that you can get your home almost TOO sealed. LEED recognizes that fact and urges whole-home ventilation systems built into the HVAC mechanisms.
Basically the ventilation system is designed to bring fresh air into an otherwise very sealed home. The air quality and conditioning is maintained because the incoming air is sent through the HVAC system before hitting your lungs (and not just through a hole near an electrical socket). The ventilation system that we opted for includes a heat exchange mechanism to increase the efficiency of the system (we heat/cool the outside air via a heat exchange mechanism before it hits the HVAC system itself).
One of the downsides of little natural ventilation is that LEED discourages fireplaces – even those touted as environmentally friendly – because they can still deplete oxygen levels in very sealed homes. You can install one, but only if power ventillated and sealed. We didn't like that asthetic, so we opted for no fireplace (which was disappointing).