Energy Audits and HERS Rating for Existing Homes


A home with HERS index and dollars (saving money)

A HERS energy audit for an existing home includes a complete assessment of your home’s “Thermal Envelope”. The thermal envelope idea is that the conditioned space (heated and cooled) within your home wants to be completely surrounded with an insulation barrier between you and the unconditioned elements outside. Breaks in the thermal envelope greatly compromise the ability of your heating and cooling systems to meet your conditioning needs.

National model energy codes for building first appeared in the 1970s, largely due to the energy and economic crises during that decade. The first national code for residential and commercial buildings came out in 1975.

All homes that were built prior to 1975 were built without any mandated insulation levels. Since 1975 insulation and efficiency standards have been continuously updated as the benefits have been more completely recognized and understood.

It’s easy to tell efficient houses from inefficient houses in the winter when snow covers house roofs. On well insulated houses the snow stays looking like a thick white blanket. On poorly insulated homes there are ice dams and icicles at the roof edge.

What is included in an Energy Audit for Existing Homes

An energy audit of your existing home will include the following elements:

  • Visual inspection of attic and basement
  • Assessment of mechanical equipment age, condition and efficiency
  • Assessment of appliance efficiency
  • Blower door test for building air leakage
  • Thermal imaging (weather permitting) of heat loss

Learn more about the HERS ratings process and how a HERS rating is calculated and scored.


Attic and basement

When we inspect your attic and basement we are looking to assess the thermal barrier between space which is heated and cooled (conditioned space) and space which in not intended to be conditioned. An incomplete or ineffective thermal barrier results in heating and cooling losses to which cost money and result in less comfort in the conditioned areas. Many older homes have partial thermal barriers which are ineffective.

Mechanical equipment

Many older homes have heating, cooling, and hot water heating equipment which is over 20 years old. In recent times technological advances have led to options in equipment which offer far greater efficiency. Many gas and propane furnaces and boilers are over 95% efficient.

Electric air source heat pumps are available which can replace older oil fired systems and offer great cost savings and efficiency upgrades. “Mini-split” (air source heat pump) systems are available to provide heating and cooling without ductwork. Hot water heating options now include on demand heaters and heat pump heaters. Advances have been made in cooling system efficiency as well. We assess and make recommendations where upgrades offer potential for cost savings or added comfort

Appliance Efficiency

We’re all familiar with the yellow tags that come on appliances now that rate how efficient that they are relative to other available models and the Energy Star label. Here’s how much Energy Star appliances can save compared to other current options:

Refrigerators 20%
Dishwashers 30%
Washing machines 25%
Dryers 20%

These figures are comparing Energy Star appliance options vs. other current options. If you have appliances that are over 15 years old then potential savings are even greater. For more information visit Energy Star - Appliances

Blower door testing

A blower door tool to identify house leakage

In trying to identify weak points in your house’s thermal envelope one of the best tools is a blower door. In a blower door test one of your exterior doors is sealed off with a metal frame and nylon cover which has a hole for a big fan. When the blower door is set up all windows and doors are closed, and the fan is set up to blow air of your house which depressurizes the house interior. When the fan is running the rate of air leakage can be determined and compared with the code standard as well as historical data of similar age homes.

In addition, the blower door test allows an opportunity to identify the source of air leaks. With the fan running we inspect the house room by room and feel where air is leaking in. This process is assisted by a smoke pencil which can indicate smaller leaks. We inspect connections to unheated basements and attics in this same manner.

The information and diagnosis of a blower door test provide a great tool for identifying potential areas which can be remediated. Some homeowners perform a post-test following air sealing and insulation upgrades.

Visit the HERS Rating Process page for more information and a video on how a blower door test works.

Thermal imaging

Infrared thermal imaging allow us a way to see into your walls to find out the state of your thermal envelope without tearing your walls apart. In older homes this an invaluable tool. Thermal images depict temperature differences. In residential use we can look at walls, roofs, foundations, doors, and windows. The images that we see in the infrared pictures show us where heat is being transferred. In our area the best time of year to use this technology is during the cooler months when there is the greatest difference in temperature between conditioned space and outdoor temperatures.

Thermal imaging is an effective way to direct remediation efforts. Thermal imaging is enhanced when used in combination with a blower door.

Visit the energy.gov website for more information on how thermographic inspections work.