Home Energy Audit: Evaluating Efficiency

Don't dive into energy efficiency home improvements without a plan.

Before you replace windows and doors, insulate the attic or install new siding, find out exactly where the home is leaking energy and dollars. The best way to do this is to get a home energy audit-- an evaluation of your home's energy performance. Energy audits generally cost between $250 and $350, depending on how long it takes for the energy auditor, or rater, to get to your home.

Jeff meets with the energy auditor

Jeff Wilson paid $350 for a Home Energy Rating System (HERS) audit, which is administered by the Residential Energy Services Network (RESNET). RESNET trains HERS raters to evaluate the energy efficiency of your home, and they come prepared with tools to help you decide where to start making repairs. "The nice thing about a HERS rating is that it gives you a cost-benefit analysis so you can make better decisions," Wilson says. Wilson learned he might as well be leaving a window wide open, year-round. That's how much air was passing through all of the leaky joints and weak walls and windows of his home. It didn't help that when he knocked out a knee-wall in his kids' bedroom to construct a built-in bookcase, he didn't properly seal the area. A daylong visit from the HERS rater covered every mechanical aspect of the home (HVAC, appliances, lighting) and its envelope (windows, doors, insulation, roof). The rater conducted a blower door test to assess the leakiness of the house, and a duct test to locate leaks in the HVAC duct system. He checked electrical outlets -- for, yes, more leaks -- and compiled all this information into a handy report with charts.

Jeff Knocks a Hole in the Kids' Bedroom Wall

Wilson learned he might as well be leaving a window wide open, year-round. That's how much air was passing through all of the leaky joints and weak walls and windows of his home. He didn't know it at the time, but he had made matters worse when he knocked out a knee-wall in his kids' bedroom to construct a built-in bookcase (as seen in this picture). That's because he didn't properly seal the area afterwards.

The Blower Door Test

A day-long visit from a HERS rater involves inspecting every mechanical aspect of the home (HVAC, appliances, lighting) and its envelope (windows, doors, insulation, roof). The rater conducts a blower door test to test the leakiness of the house.

The Duct Test

The rater also conducts a duct test to find additional leaks. He checks electrical outlets—for, yes, more leaks—and compiles all this information into a handy report with charts.

Diagnosing the House

Here are some highlights of Wilson's HERS test, what the rater determined about the home's efficiency, and what you might experience if you enlist a HERS auditor. Blower door test: A fan mounted inside the doorway is connected to a digital pressure meter. This way, it can measure any air escaping or entering the home. This is how Wilson learned that his home's "holes" amounted to 160 square inches of total open space—a sizeable gap. Infrared imaging: Wilson got his HERS test in the summer, so the rater used an infrared camera to show where heat was leaking into the air-conditioned home. Humidity is a problem in his region, and the reason most people crank up the A.C. during summer weather, Wilson says. So keeping humidity out can reduce energy use to keep the home "cool," when really the A.C. is mostly removing moisture from the air. Electric outlet tests: By testing individual switch plates, Wilson learned that their recessed lighting is an energy suck.

The Analysis

The HERS rater collected data from tests and, using a software program, compiled a detailed report to help Wilson understand exactly where his home stood on the efficiency spectrum. The Wilsons scored an 87 HERS rating, with 100 being the HERS baseline. Higher than 100 means a home is relatively inefficient; a score of zero means the home uses only the energy it creates, such as through solar or wind power. Wilson wasn't disappointed with his score, 87, but with a goal of net-zero, he has a long way to go with his Deep Energy Retrofit (DER) plan.

Energy Star Insulation

Interested in making energy efficient upgrades, but don't know where to start? Many municipalities and utility companies offer rebates or free energy audits under a variety of programs. Search www.dsireusa.org, the Database of State Incentives for Renewables & Efficiency, to find out where these programs are available. You'll find a map where you can search your area for HERS rating or other energy audit offerings. RESNET also administers online home energy surveys. "There is so much conflicting information about the best, least-expensive solutions, what homeowners should do, what contractors should do," Wilson says. "By checking incentives, you can find out which items on your HERS list you could do at a vastly reduced rate right now."

Maximize Your Audit

Wilson suggests these tips for making the most of a HERS test:

  • Monitor your home energy use before the HERS test, preferably up to 6 months in advance. This gives you historical data to provide the rater.
  • Be at home during the audit so you can discuss your goals with the rater.
  • Ask lots of questions during the process.
  • Request a range of testing information, from the actual energy use data to solid steps you can take in the short-, medium- and long-term to tighten up your house.

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Wilson's rater used a thermal image camera to check the heat leakage around the recessed light in the top of the cabinet in the main bathroom. Wilson learned that recessed lighting can be one of the worst culprits in air leakage into unconditioned space and is correcting it as part of his DER. The Wilsons will have another HERS rating done in early winter to determine how effective their DER was in eliminating leaks. Their goal is to get a score of zero.