NADCA Energy Research Project

Fouled Coil: This photo shows the upstream side of a heavily fouled A-Coil, which is essentially matted over with dust and other contaminants.

Heating, ventilation and air conditioning a home or small commercial building is a big job that requires a lot of energy. In fact, this activity accounts for 30 percent of the energy used in an average home or small building. In addition, heating and cooling larger buildings is an even tougher job and accounts for up to half of the energy use in such buildings. On the whole, heating, ventilation and air conditioning systems are by far the largest sources of energy use within a home or building. Ironically, heating and cooling systems tend to be poorly maintained. These systems, which are used every day of the year, get dirty and can become heavily contaminated with dirt, dust, animal dander, and more. Further, heating and cooling systems in new homes and buildings are often heavily fouled – even before occupants move in. Contaminated heating and cooling systems can be problematic for occupants. These systems contribute to poor indoor air quality in the form of increased airborne particulate and reduced thermal comfort. Fouled systems are also prone to failure. And from a cost perspective, these systems also use more energy than clean systems.

The Importance of Air Flow

Dirty Duct: Accumulations of dust and debris within HVAC ductwork can contribute airborne particulate within a home or commercial building, while also reducing air flow and increasing energy consumption and related costs.

When it comes to having a productive, energy-efficient heating and cooling system, air flow is everything. Increased air flow equates to better performance. But when systems become fouled, air flow is reduced. Dirty filters, clogged coils, fouled blowers and other components – all of these things impede air flow and lead to increased energy costs. The solution is to have the heating and air conditioning system professionally cleaned. You may be familiar with the term air duct cleaning, but this is actually a bit of a misnomer. Professional cleaning for a heating and air conditioning system entails cleaning not only the ductwork, but also the vents, registers, blower, coils, and other components – the surfaces that are exposed to the air flow within the system. Complete cleaning of the heating and air conditioning system is a highly specialized cleaning service that differs from the routine maintenance provided by the technician sent out to clean and adjust the furnace. Complete cleaning of the heating and air conditioning system is an important aspect of keeping the system operating at peak efficiency.

The NADCA Energy Savings Research Project

Clogged Air Duct: In extreme cases such as this, ductwork can become totally clogged, totally restricting air flow.

So how much does it cost to operate a fouled heating and cooling system? That is the question asked by the National Air Duct Cleaners Association (NADCA), a not-for-profit trade association representing companies around the world that inspect, clean and restore heating and air conditioning systems. In 2008 NADCA initiated a project with researchers from the University of Colorado at Boulder (CU) to conduct an in-depth study of this issue. The University has extensive research experience and is home to the Larson Building Systems Laboratory, one of the world’s most technologically advanced facilities for researching heating and cooling systems. The purpose of the NADCA research study was to correlate the substantial energy savings that can be attained through complete cleaning of fouled heating and cooling systems.

Research Overview

Dirty Fan: Blowers such as this can become heavily contaminated and require cleaning for maximum efficiency.

Researchers started this project by scouring the Internet and other sources to find literature produced through similar research. Using available literature, researchers developed a computer model designed to quantify the energy savings that could be attained through cleaning heating and cooling systems. From there the researchers conducted a laboratory analysis – they experimented on a house that is contained completely within the Larson Lab – as part of an effort to fine-tune and confirm the computer model. Finally, researchers conducted two field trials to assess the accuracy of the computer model. Through this process, researchers came to realize that there was no comprehensive data available to quantify the savings that can be achieved through cleaning of heavily-fouled systems – the types of systems regularly encountered by NADCA members. (For purposes of this research, “Heavily-fouled” systems are defined as systems where complete cleaning results in a pressure change of at least 30 percent. Pressure change is simply an easier way to measure air flow.) Because of the data limitations, the calculations in the computer model were based on data collected from lightly-fouled systems – systems that are not very dirty.

Key Findings

According to the results of the study, cleaning even lightly-fouled systems can produce substantial energy savings. These findings are based on complete cleaning of heating and air conditioning systems in accordance with NADCA’s ACR 2006 Standard, which includes cleaning ductwork, coils, blower, other air-side system components, and changing the filter. Based on the initial research, cleaning a lightly-fouled system provides, on average, an 11 percent savings off of the energy used for heating and air conditioning.

Next Steps

Cleaning heavily-fouled systems is expected to produce an even greater savings than cleaning systems that are essentially clean. Given the critical importance of air flow, this could be construed as common sense. However, in order to confirm this expectation, NADCA has initiated a broader research effort to quantify the energy savings that can be achieved by complete cleaning of heavily-fouled heating and cooling systems. This research involves collecting data on systems before and after cleaning, and using this data to calculate energy savings.


It takes a lot of energy to heat and cool a home or building and in fact, the systems used for this purpose account for the majority of energy use.  These systems – even in new buildings – tend to be dirty, and become more heavily fouled through everyday use. Fouled heating and cooling systems can also be problematic for occupants, contributing to poor indoor air quality, system failure and increased energy use. Researchers have proven that cleaning even lightly-fouled heating and cooling systems can result in energy savings of 11 percent. In addition to these savings, consumers who have their heating and cooling system cleaned can benefit from improved indoor air quality, reduced maintenance costs and extended life expectancy for the heating and cooling system. While not yet confirmed, cleaning heavily-fouled systems is expected to produce even greater energy savings.

NADCA Energy Research Study

For decades the National Air Duct Cleaners Association (NADCA), has been educating consumers on the process and benefits of air duct cleaning. Currently there is research study underway to measure the correlation between energy pressure drop and energy savings.

NADCA Energy Research Study

In February 2008, NADCA entered into a partnership with the Colorado University to conduct a research project that will provide members with a tool for estimating the energy savings associated with HVAC cleaning and restoration projects. The research project was also commissioned to develop a field-testing protocol for NADCA members that will facilitate collection of data to provide broader support for linking HVAC cleaning and restoration to energy savings.

Current Findings and Test Results

NADCA presented the current results of the test at the 2010 Annual Meeting.  Comparisons were made by testing air flow rates when the filter, furnace, and evaporative air conditioner coil were fouled and again when the components were clean.

It was found that a dirty filter increased the filter pressure drop, system pressure drop and reduced the air flow of the ventilation system.

Surprisingly, a clean furnace and evaporative air conditioner coil increases initial energy consumption, but lessoned the amount of time that the furnace an air conditioner had to operate to achieve the desired room temperature. Though there was initial higher energy consumption, there was a net gain in overall energy efficiency.

While further data and testing is required, the current the findings show that proper exchange rate and selection of the furnace filter, routine cleaning of the evaporative air conditioner coil, and sealing of air ducts offer the greatest benefits to energy savings.

Further Testing Underway

Currently NADCA is receiving further test results from companies engaged in the assessment, cleaning, and restoration of HVAC systems.  These test results are being sent to the University of Colorado for further interpretation.

Air Pollution in Energy Efficient Homes

Air sealing the building envelope is one of the most critical features of an energy efficient home.  As new homes grow increasingly tighter to achieve ever higher levels of energy efficiency, the potential for indoor air pollution also increases.

Modern Construction

During construction, there are hundreds of penetrations through a typical home’s exterior. These gaps and holes are often incurred during framing, and from penetrations for wiring, plumbing, and ducts.  Air leakage accounts for 25–40% of the energy used for heating and cooling in a typical home.  To make a home energy efficient, these gaps and holes are closed and insulated to prevent the loss of conditioned air.

Indoor Air Quality Concern

Good indoor air quality is achieved by reducing or eliminating sources of indoor air contamination and providing sufficient fresh air through the heating and ventilation system.  While older homes were not energy efficient, they typically did not have problems with indoor air quality because they allowed for fresh air to freely circulate within the home.

As new homes grow increasingly tighter to achieve ever higher levels of energy efficiency, potential indoor air pollution also increases since many conventional building materials emit volatile organic compounds like formaldehyde.  While energy efficiency is important, gains in energy efficiency, especially in new homes, should not come at the expense of deterioration of indoor air quality and corresponding adverse health impacts.

Source Elimination and Control

The best way to address indoor air pollution is through aggressive source elimination and control.  Pollution should be prevented or reduced at the source whenever feasible.

  • Building materials:  If you are having the home constructed or remodeling your home select materials that do not emit volatile organic compounds.
  • HVAC System: Make sure your HVAC system distributes the minimum level of outdoor air throughout the home using whole-house mechanical ventilation.
  • Sealing Air Ducts:  Sealing ducts can help improve indoor air quality by reducing the risk of pollutants entering ducts and circulating through your home as well as preventing the loss of conditioned air.
  • Air Duct Cleaning: Ventilation systems distribute the air you breathe. Have the air ducts and HVAC system professionally cleaned to remove construction debris and pollutants.
  • Monitor use of household cleaning supplies:  Some household chemicals can be extremely dangerous.  Choose environmentally safe cleaning supplies, and make sure that the area is well ventilated.
  • Check exhaust systems:  Make sure exhaust fans are clean and unobstructed. Exhaust systems are responsible for removing moisture, odors, fumes, and carbon monoxide.