Having well-designed HVAC systems is important for achieving adequate indoor conditions and optimal costs. However, the building envelope is also important but often overlooked. Having efficient heating and cooling systems is great, but even better results are possible when the building envelope minimizes heat gain during the summer and heat loss during the winter.
Insulation acts as a barrier against heat transfer, reducing unwanted heat gains and losses in walls, ceilings and floors. However, heat can also move in and out of a building through air movement, which increases heating and cooling expenses.
- Any exchange of air between the inside and outside of a building increases the cooling load if it occurs during the summer.
- The opposite principle applies during winter, when air exchange increases heating loads.
- As air carries moisture, it can increase the load on humidification or dehumidification systems, depending on the difference in relative humidity between indoor and outdoor air.
In a nutshell, unwanted air movement through a building envelope increases the operating costs of many building systems. Therefore, reducing or eliminating air leaks is in the best interest of homeowners.
Does your building have adequate insulation and airtightness?
Air leaks also make your building less resilient during emergencies. As an example, suppose bad weather knocks out local power and HVAC systems stop working. In this case, a building that does not retain indoor air effectively can heat up or cool down very quickly.
How Air Leaks Affect Air Conditioning and Heating Systems
It's common knowledge that air conditioning systems lower the temperature of indoor air, but a lesser-known fact is that they also remove humidity. As we discussed in a previous article, high moisture content in the air causes problems like moisture damage and mold growth.
Energy costs are higher when air conditioning systems operate in a building with many air leaks, as unwanted air exchange brings heat and humidity into the building. Consider that air leaks have negative effects even when they occur between different areas of the building, for example, between air-conditioned rooms and unconditioned crawl spaces.
If you are considering an air conditioning upgrade, we highly recommend getting an air leak inspection first. By reducing unwanted air exchange in your building, you can calculate the cooling load of your new air conditioning system more accurately.
Air leaks have negative consequences all year round. Just as they overload air conditioning systems during the summer, they increase the heating load during the winter. The opposite behavior happens here: air leaks cause a loss of interior heat and, when the cold winter air is dry, there is also a large loss of humidity.
US Department of Energy recommendations for detecting air leaks
The location of some air leaks is very obvious. For example, you've probably noticed how air moves through the spaces around doors and windows, or between their frames and walls. Weatherstripping is an inexpensive and effective solution to air leaks between fixed components, and caulking is recommended for moving elements such as doors and windows.
Other air leaks are more difficult to detect and an energy audit will usually be required to identify their location. To find hidden air leaks and measure the rate of outdoor air infiltration, the U.S. Department of Energy recommends a blower door test:
- A large blower is placed at the main entrance of a home and all other doors and windows are closed.
- The blower draws air from your home, causing negative pressurization. If there are any leaks in the building envelope, outside air will begin to enter through them.
- Energy consultants can calculate the outdoor infiltration rate based on the airflow established by the blower door and measurements of pressure differences between the interior and exterior of the building.
- A smoke stick is used to locate individual air leaks. When it is moved near an air leak, the normal upward flow of smoke is interrupted by air infiltration.
- Only a calibrated blower can measure the air infiltration rate; Uncalibrated units are only useful for finding locations of air leaks.
- Blower door testing is one of the mandatory requirements to certify a home under the ENERGY STAR program.
Differences in air temperature cannot be detected by human vision, but they become evident when observed through a thermal imaging camera. Cold spots are displayed in dark colors, while hot spots appear bright, and sudden changes in temperature can signal air leaks or poorly insulated spots. Thermal imaging is very useful, but a professional energy auditor will complement it with other tools and methods – it is not recommended to rely on just one tool.
Although home energy auditors are qualified professionals, they can do their work more efficiently if you are with them during the inspection. For example, if you point out problem areas that are more difficult to heat or cool, home auditors can look for air leaks and insulation deficiencies more effectively.
Final Observations
Air leaks can go unnoticed for long periods of time, with the potential to rack up thousands of dollars in additional heating and cooling expenses. Energy audits are recommended for all buildings at regular intervals, but especially if you have noticed a sudden increase in your electricity and gas bills.
According to the U.S. Department of Energy, the average home has air leaks equivalent to keeping a 200-square-foot window open all the time. A home energy audit can identify measures that lead to energy savings of up to 30%.
When considering an HVAC upgrade, be sure to check insulation and airtightness first. Improvements to the building envelope reduce heating and cooling loads, achieving synergy with any high-efficiency equipment you purchase.
