Other Research Findings

What Building Scientists, Researchers, Utilities and Manufacturers Have Discovered

These studies have been published in various trade journals and are collected here for your information.


Pacific Gas & Electric Study
In the Summer of 1990, Pacific Gas & Electric (PG&E) hired Proctor Engineering Group to investigate the potential energy savings in residential air conditioners and forced air gas furnaces installed in the Fresno, California area.  The Fresno study was targeted at PG&E's high utility bill complaint customers.  The objectives of the study were to:

  1. Identify the major problems with existing residential air conditioning installations

  2. Identify the major problems with existing furnace installations

  3. Determine what actions could be taken to correct those problems

  4. Estimate the potential savings from those actions

The results are startling.  Here is a summary of their findings:




Airflow less than 375 cfm/ton (dry coil)


Coil Dirty or Clogged


Filter Dirty, Clogged or Missing


Refrigerant overcharged (averaged 10% above correct level)


Refrigerant undercharged (averaged 20% below correct level)


Refrigerant leak


Other (Kinked refrigerant lines, wrong capacitor, etc.)





Fan Off Temperature above 90º F


Steady-state efficiency less than 75%


Gas leak


Low heat anticipator setting (caused short cycles)


Incomplete combustion (Carbon Monoxide present)


Cracked heat exchanger





Duct leakage greater than 150 cfm (recommended maximum in this study)





House leakier than .75 air changes per hour


No wall insulation


Ceiling insulation less than R-11


Ceiling insulation R-11 to R18.9


The PG&E study identified a significant source of untapped electrical and gas savings.  In all cases the cooling energy use could be lowered by 10% to 30% without extreme effort.  In addition, these repairs have the potential to improve customer satisfaction.  


The Fresno project showed that the existing HVAC contractor infrastructure was not able to identify and solve the problems that led to the high bill complaints.  This can be attributed to a business environment that concentrates on low first cost and lowest bid.  This business atmosphere results in poor installations and inadequate time available to diagnose and repair extreme problems that exist.


Comfort Institute Commentary: Although this study was completed in California in 1990, the facts are still very relevant today all across North America.  The HVAC industry is currently experiencing the worst shortage of skilled labor in its history and a lack of students, programs and teachers will continue to worsen the situation.  With a lack of trained technicians, many contractors tend to shy away from tackling problems that require more than a couple of hours to remedy.  Furthermore, most contractors will  invest very little in education of their staff for fear of making the employee so valuable that the competition will attempt to lure them away with higher wages.  Be sure that you hire a qualified contractor.

North Carolina Alternative Energy Corp.
This non-profit organization examined air conditioning manufacturers' efficiencies versus the actual efficiencies that resulted after installation.

  • 90% of the units tested exhibited some sort of energy-wasting problem

  • 50% had an improper refrigerant charge

  • 40% failed to meet minimum airflow criterion. 20% were barely inside the range specified by manufacturers.

  • A deficiency of only 20% in indoor airflow reduces the efficiency rating by 17%.

  • A 15% return air leak from a 120° attic could reduce efficiency by 50%!

Texas A&M University
A 23% refrigerant undercharge could result in a 52% efficiency loss.    


Florida Solar Energy Center
Researchers found that by repairing leaking ductwork, cooling energy was reduced by an average of 17.4%.  


A typical heat pump would lose almost 50% of its efficiency after 20 years, even if a typical "dust stop" filter had been installed.  Also in 20 years, a unit's efficiency could degrade  by 50% if it is not properly maintained. This would double the energy cost!


Louisiana State University & Gulf States Utility
Consumers could save about $30 per month just by making sure that their air conditioning system is cleaned and serviced regularly.

  • LSU determined that without proper air filtration, over time, air flow can be reduced by over 30%

  • Capacity can be reduced by over 12%. 

HVAC Manufacturers
Data shows a 13 Seasonal Energy Efficiency Rating (SEER) condensing unit matched with an old air handler would decrease the SEER to 9.2, resulting in 30% less efficiency.


PLEASE NOTE: None of the organizations mentioned above are affiliated with Comfort Institute in any way except as an active  participant in the HVAC industry.  Their presence here does not constitute any form of endorsement by the parties mentioned.  The information is factual and presented without modification except to clarify technical terms.  The actual source materials for these studies are available from the authors in most cases.