Keeping your world up and running.®

At a log home: energy inspection utilizing thermal imaging and blower door technology

See process and results at a modern log home

By Greg Jourdan

July 2012

Sealing and insulating the "envelope" or "shell" of your home - its outer walls, ceiling, windows, doors, and floors - is often the most-cost effective way to improve energy efficiency and comfort. The US Environmental Protection Agency (EPA) ENERGY STAR program estimates that a knowledgeable homeowner or skilled contractor can save up to 20 percent on heating and cooling costs (or up to 10 percent on the total annual energy bill) by sealing and insulating a home.

Whether your home is a traditional stick frame house, manufactured home, or custom log cabin, single story or multistory, air leaks within your home are a form of energy loss and need to be eliminated to minimize energy losses and reduce utility costs.

Utilizing modern tools such as thermal imaging, blower door technology, and duct testing can help the homeowner and energy utilities identify key energy losses and repair components of the structure, while conserving overall energy within the home. This article will primarily discuss thermal imaging used in conjunction with blower door technology, emphasizing the importance of sealing and insulating your home. However, heating, ventilating, and air conditioning (HVAC) duct losses can contribute to large energy losses, as well. Thus, duct testing and repair should not be ignored, but are not discussed in this article. Note that the pictures in this article are of a modern log home, but the principles discussed here apply to all types of residential and commercial construction.

Taking thermograms

Thermal imaging cameras detect energy in the infrared range of the electromagnetic spectrum (roughly 7000 - 14,000 nanometers or 7 - 14 µm) and produce images of that energy, called thermograms or thermal images. The Fluke Ti-32, which was used for this article, has an infrared spectral band sensitivity of 7.5 μm to 14 μm (long wave).

the orange and red areas show hot air leaking to the outside.

Figure 3. Outside the home, the orange and red areas show hot air leaking to the outside.

Cooler air infiltrating between the logs of the wall.

Figure 4. Cooler air (dark blue and black) infiltrating between the logs of the wall.

Homeowner points out cool air infiltration

Figure 5. Homeowner points out cool air infiltration.

Setting up the blower door device

Figure 6. Setting up the blower door device.

Using a thermal imager with blower door

Figure 7. Using a thermal imager with blower door temporarily installed, to look for air exfiltration. Be careful to understand the impact of solar loading.

Since infrared energy is emitted by all objects above absolute zero, thermography makes it possible to see energy losses in a home without visible illumination. The amount of energy emitted from the home increases with temperature; therefore, thermography allows you to see variations in temperature in a home. When viewed through a thermal imaging camera, warm objects or heat leaking out of, or into, a house stand out well against cooler backgrounds; thus energy losses or gains from the home become easily visible, day or night, winter or summer. (See Figure 3.)

Thermal imaging cameras reveal temperature changes and differences in real time that are invisible to the naked eye. This technology allows testing for energy losses without requiring contact with or damage to the building. Infrared cameras are therefore very suitable for home inspections, as no exterior or interior finishes need to be taken down and you can inspect large areas in a short time. Infrared thermography has become one of the most trusted and common residential inspection tools available. The real-time picture of a thermal imaging camera shows instant and documentable areas of potential energy loss. Notice in Figure 4 that the cold air is falling into the room and hot air is rising up onto the ceiling.

What's to be gained from a thermal imaging inspection?

Homeowners, residential property managers, real estate agents, insurance companies, and contractors all need residential inspection services, and will be best served by a thermal imaging inspection. Homeowners wish to preserve and protect their investment, as well as lower energy costs. Property management firms, or those who own large real estate units, benefit from being apprised early of insect infestations, moisture issues, and mechanical or electrical problems. Additionally, a property owner with a large building, or a row-housing complex with a shared front façade or roof, can use the information from an infrared inspection to make economically smart decisions.

Many times the homeowner or the general contractor who built the home is surprised to see the air leaking or energy losses. In Figure 5 a homeowner points out the air leakage penetrating the home.

Air leakage testing using the blower door

Most state energy codes require air leakage testing for all new houses. The test must be performed using a blower door device, which consists of a large fan, a door-panel system, and a manometer (pressure gauge) to read house and fan pressures. See Figure 6. All penetrations in the building envelope must be sealed, including those for utilities, plumbing, electrical, ventilation, and combustion appliances.

The air leakage test is only required (in most states) for new construction. However, it is a good recommendation to have this test done when an energy inspector is evaluating your home with a thermal imager, because it will help to pinpoint specific air leaks and problems in the structure.

A blower door has a frame and shroud that fit inside a doorframe. Mounted in each blower door is a variable-speed fan that allows it to induce pressure on the inside of a dwelling. Instrumentation that accompanies a blower door includes pressure gauges with which a technician can measure the flow of air through the fan as well as the pressure differential between the living space and the outdoors. With a blower door in operation, a technician armed with a thermal imager and a pressure gauge (to verify the pressure differential in various parts of a dwelling) can find areas that contribute to the loss of conditioned air (heated in the winter and cooled in the summer) by convection. See Figure 7.

What does this mean to you?

In construction projects, the building contractor who uses thermal imaging technology will have an advantage by being able to identify clear problems and prove that repairs have been completed correctly. Insulation, restoration, and repair costs can be minimized by conducting an infrared inspection before valuations, transactions, or major system upgrades. A thermal imaging camera detects small temperature differences and can be used indoors and outdoors, and on wood, concrete, drywall, and electrical wiring. This technology can be used in the following applications:

  • Conditioned air leakage
  • Missing, mis-installed, or damaged insulation
  • Door and window seal inspection
  • In-floor heating system inspection
  • Inspection for areas of unexpected condensation
  • Moisture detection within the structure, floor, and roof
  • Covered openings searches within walls
  • HVAC and electrical systems inspections
  • Pest inspections

Infrared inspections were seen in the past as affordable solely for large commercial organizations, but now thermal imagers are more available and lower in price. Homeowners want to use the technology to find sources of energy losses: air leaks, insufficient insulation, and moisture problems. Over time, correction of these problems will save the homeowner a significant amount of money.

Log home after it was sealed and caulked

Figure 8. Log home after it was sealed and caulked.

Remedies for air leaks in a residence

  • Seal air leaks throughout the home to stop drafts
  • Add insulation to block heat loss in winter and heat gain in summer
  • Choose ENERGY STAR qualified windows when replacing windows

You can hire a contractor who is certified with special diagnostic tools, such as thermal imagers and blower doors, to pinpoint and seal the hidden air leaks in your home.

Figure 8 shows the log home with chinking after the house was sealed. Sealing and chinking this log home was very effective, but the contractor failed to seal the cracks in the log walls, and additional sealing will be required to completely minimize energy losses.