The home energy audit: What to expect
By Adam Kahn
Energy waste is my enemy. As a certified Building Analyst, my job is to assist homeowners in their battle against energy waste and cold rooms, as well as ensure that their home operates safely.
Through a methodology referred to as a Whole House Approach, a building analyst documents your home’s current energy effectiveness. Specialized instruments are used to assist in accurately measuring your energy consumption. This approach considers the house as one interconnected group of systems. For example, it stresses the importance of pressure differentials in your house.
Here's what a typical energy audit will consist of, and what you can expect when a professional conducts one in your home.
An energy audit can last from two to four hours, depending on the size and complexity of the house and the systems within. It is not required, but it helps the person conducting the energy audit if you're able to provide a building sketch and any details on the building's history, which can be found on most county websites. This information is important because it will give the auditor an idea of construction methods and building materials used in the construction of your home. In addition, current and historical utility bills (usually gas and electric) will assist in setting a baseline for energy improvement and estimated savings.
After the initial data is reviewed, the building analyst will inquire about any areas of the house that may be displaying symptoms of energy inefficiency. These questions will focus on drafts, cold floors, icicles, condensation, and more. The answers will help the inspector pinpoint problem areas that may require a more thorough investigation. Typically, we collect information specific to the appliances, thermostat, electronics, lighting, toilets & showerheads and other common energy-consuming devices.
Once this survey of device consumption is complete, the building analyst will perform a physical inspection of the building materials and assembly. I prefer to start in the basement because typically that is where the furnace and water tank are located.
Building analysts will conduct a few performance tests to ensure safe operation of the combustion appliances. When it comes to combustion, making sure exhaust fumes are properly escaping the house is important. This is ensured by measuring pressure. First, the analyst will determine a baseline pressure state measured against the outside of the house.
Once a baseline is determined, the first test a building analyst will run is a worst-case spillage test. The worst case test is performed by creating as much negative pressure in the combustion zone as possible; typically turning on all bath fans, kitchen fans, whole-house exhaust fans, clothes dryer -- any mechanical device that expels air -- will establish the worst case depressurization of the house. A measure of spillage (under these worst-case conditions ensures that the exhaust from the naturally aspirating appliances is sufficient not to pollute indoor air quality.
The draft pressure from the appliance will also be measured using a monometer to assess the appropriate level of draft for the size of the appliance. These tests are followed by a combustion test, which measures the efficiency of the gas burners by measuring the presence of partially combusted gas particles.
The building analyst will use an instrument called a combustion analyzer to assess the efficiency. Most HVAC companies have this equipment, and will use it during a tune up of your system. The efficiency and size of your appliance will help your building analyst determine the percentage of total consumption your heating system in relation to other systems in your home. In most instances, the furnaces and water tanks are operating at their rated levels; only once in my experience have I seen one furnace read lower than rated, this furnace was about 45 years old and was located in a crawlspace with a dirt floor.
It is important to have your combustion appliances serviced once every few years. Once these tests are performed, the building analyst is ready to move on to other tests not involving the appliances.
After inspecting the basement and performing combustion testing, the building analyst will likely make his next stop in the attic. In the attic, he will document the qualitative aspects of the home’s insulation as well as the quantitative measure of R-value of the insulation. Most attics I encounter contain insulation levels one half of what is required by code. The Department of Energy recommends for our region of the country an R-value of 38 for ceilings.
After this visual inspection, the building analyst is ready to perform a blower door test. A blower door test is used to assess the air leakage in a house. The blower door assembly fits in an exterior door jam. This equipment has a calibrated fan and pressure gauge to measure the air leaks in a house while running. During this test, any combustion appliance should be shut off for safety and all windows and exterior doors should be closed to simulate winter conditions.
The fan will throttle up to depressurize the house to a negative 50 Pascals (a unit to measure pressure). At this point, the pressure computer, called a manometer, will give a reading in cubic feet per minute (CFM) to quantify the amount of air flowing through the house. Each house has associated with it a calculated Minimum Vent Guideline (MVG). This measure is the lowest point a house can be sealed to without adding additional ventilation. Staying above the MVG will preserve clean breathing air and interior moisture control.
The prevailing motto in the air sealing business is to "seal tight, ventilate right." This motto simply means, that sealing a house as tight as possible is appropriate, but when you do that considerations have to be made to add a mechanical ventilation system. This system is designed to create enough make-up air to preserve air quality and safety.
While the blower door is running, the analyst will inspect the interior of the house for air leakages either with a smoke pen, a thermal imaging camera, or a combination of the two. These instruments will assist in identifying problems that need to be addressed through air sealing measures.
During the blower door test, a thorough re-inspection of the house with the diagnostic tools will pinpoint most areas. Air sealing and insulating a house to specifications are the best investments because of the reasonably low cost and effectiveness. Air sealing and insulating can achieve savings in excess of 20%, depending on the age and construction type of the home.
After these tests and inspections are performed, your building analyst will explain options for rectifying the problems identified during the Home Energy Assessment. In most instances, the inspection will be documented in the form of a comprehensive report that models your current energy consumption and calculates potential energy savings and investment returns. In some cases, the report will be generated while you wait. Other times it may take a few days or a week to provide the report. Once you have received your report, it is important to have a conversation with your building analyst to discuss the measures he or she is recommending, as well as any other questions.
It's recommended to use a credentialed professional when gettting a home energy audit. There are two major credentialing organizations in the U.S. -- the Building Performance Institute (BPI) and the Residential Energy Services Network (RESNET). Both offer training and certification, enforce standards in the industry, and help connect homeowners to energy auditors.
Air sealing and insulating can achieve savings in excess of 20%, depending on the age and construction type of the home.
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