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Reference Publication: Proctor, J and D Parker (2001). Hidden Power Drains: Trends in Residential Heating and Cooling Fan Watt Power Demand. FSEC-PF361-01, Florida Solar Energy Center, Cocoa, Florida.

Disclaimer: The views and opinions expressed in this article are solely those of the authors and are not intended to represent the views and opinions of the Florida Solar Energy Center.

Hidden Power Drains:
Trends in Residential Heating and Cooling Fan Watt Power Demand

Danny S. Parker
Florida Solar Energy Center (FSEC)


John Proctor, P.E.
President, Proctor Engineering Group
San Rafael, California



This paper compiles power draw, air flow, and static pressure measurements of residential air handlers taken during nine separate field tests of space conditioning systems in Arizona, California, Florida, Nevada, and Canada. The field tests show that air handler devices do not meet basic performance standards and that the interactions between components combine to further degrade overall system efficiency. The findings support conclusions from previous research in Canada that called for a systems approach to improving air handler efficiency. This study reports that fan power consumption in U.S. air conditioners is about 40% higher than estimates used in the DOE Central AC and Heat Pump Test Procedure when rating air conditioners. Fan power draws approach 1000 watts, similar to adding a 1000 watt electric resistance heater in the air stream. The low assumed watt draw masks the need for continued improvements in equipment performance and creates operating cost penalties - not advantages - for customers. Application of high-efficiency filters without attention to static pressure considerations would exacerbate these effects by raising air horsepower and watt draw. The paper summarizes the field test data and suggests a systems-based approach for component and product improvement.


In the early 1990s Canadian researchers investigated the influence of residential air handling devices on furnace energy consumption and estimated the potential efficiency improvements offered by these devices. One study conducted by Canada Mortgage and Housing Corporation (CMHC, 1993) concluded that residential furnace air handler efficiencies in terms of air moving load external to the furnace were less than 10%. This poor performance was attributed to a number of causes, including fan inefficiency, motor inefficiency, and poor cabinet air flow design.

Air handler flow rates on furnaces have increased about 25% in recent years. This is in spite of a general reduction in installed furnace size. This increase in flow produces higher efficiency furnaces (when efficiency is measured as heat output per heating fuel input) but duct systems have not been modified to allow for the higher flows. The resulting inadequacy of duct design causes an increase in external static pressure that adversely influences fan energy use, air flow, and total system performance. While permanent split capacitor motors have improved motor efficiencies, the fan watt draw per 100 cfm has remained almost constant.

Air Conditioner and Heat Pump efficiencies have also risen substantially in recent years. The watt draw of the compressor has been substantially reduced on these machines, so that the air handler fan watt draw has become a larger part of the total watt draw.

At the same time, more effective air filtration is being added to air handlers. The proposed ASHRAE Standard 62.2P, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings, if adopted, will further the use of more effective filtration devices. These devices could increase external static pressure beyond current levels that already exceed Department of Energy AC and Heat Pump Test Procedure default values. Fan watt draw, easily 17% of the total residential air conditioner energy consumption, will become a greater contributor to overall unit energy use, secretly degrading air conditioner efficiency.

Beyond inadequate duct sizing, air movement through space conditioning systems is compromised by the non-aerodynamic intake and exit conditions common in cabinet and heat exchanger designs. Improvements are also available in fan and motor efficiencies, but the system as a whole needs to be addressed. The electrical consumption of air handler fans will become increasingly important in coming years as the penetration of air conditioning into the residential market continues to grow. Market penetration has increased by 79% in the Northeast US and by 45% in the Midwest US between 1984 and 1994.

Since the CMHC report on furnace air handler inefficiencies, nine additional field tests conducted in the U.S. and Canada have produced corroborating data. These tests extend the significance of CMHC’s observations to U.S. air conditioning systems and build on its original findings pertaining to Canadian furnaces. The field tests were individually sponsored by a variety of utility company and industry research organizations.

The measurements of fan power consumption, external static pressure, and air flow reported here also show that the DOE test specifications used in calculating air handler performance efficiencies misrepresent the actual conditions under which the equipment operates. Utilities and manufacturers alike look to equipment SEER and HSPF ratings when planning residential marketing and energy conservation programs, and customers use these ratings when comparing equipment options. The discrepancy between assumed and actual air handler performance is creating unrealistically high air conditioning and heating systems efficiency ratings which mask the need to improve the efficiency of this equipment.

Measured indoor Fan Watt Draw, External Static Pressures, And Air Flow

The nine field tests reported in this paper were conducted from 1994 to 1998 under sponsorship of various utility companies and research organizations. The tests include a 1996 study of 28 residential air conditioner systems installed in 22 new houses in Phoenix, Arizona; a 1995 field test of 40 residential air conditioner systems used in existing housing in the Cochella Valley in central California; a 1995 test of 40 residential air conditioner systems installed in new houses in Las Vegas; a 1996 test of 37 residential air conditioner systems installed in new houses in Las Vegas; a 1998 study of 5 new evaporative cooled air conditioners installed on existing furnaces and duct systems in houses located in various areas of California; a 1995 study of 32 near new furnace systems in houses across Canada; a 1995 study of 39 pre-1990 furnace systems operating in houses across Canada; a 1997 study of 9 air conditioner systems found in existing residences in central Florida; a 1998 study of 15 air conditioner systems installed in newly constructed townhouses across New Jersey.

The results are replications from three independent organizations in a wide variety of areas. The performance characteristics of these systems are presented in Table 1.

Table 1. Measured Air Handling Equipment Performance Data for North American Installations.


Study Location
equipment and housing type

Number of Units in Sample

Average Capacity (tons)


Average Inside Fan Power (watts)

Average AC inside coil air flow

Average Watts per unit of air flow (W/1000 cfm)

Average External Static Pressure (IWC)

Blasnik et al. 1996

Phoenix new







Proctor et al. 1995

Cochella Valley California existing







Blasnik et al. 1995a

Las Vegas 1 new







Proctor et al. 1996

Las Vegas 2 new







Proctor and Downey, 1998

California Replacement







Phillips, 1995

Canada near new mostly non-AC, heating speed







Phillips, 1995

Canada pre 1990 mostly non-AC, heating speed







Parker and Sherwin, 1997

Florida existing







Proctor et al. (previously unpublished)

New Jersey new townhouses







External Static Pressure And Fan Motor Energy Consumption: Standard Assumptions vs. Field Data

The standard assumption for external static pressure, according to DOE test standards, ranges from 0.1 inches of water column (IWC) for 2-ton residential units to 0.2 IWC for units larger than 3.5 tons. As shown in Table 2, the external static pressure values measured in field tests representing both new and existing construction, are two to four times higher than DOE assumptions. The measured values for the field test units ranged from 0.41 IWC to 0.55 IWC. This is at least twice the value assumed for larger (3.5+ ton) units.

Table 2. Comparison of Static Pressure and Fan Motor Energy Consumption Test Standards with Actual Field Data for Air Conditioners.


External Static Pressure

Fan Motor Energy Consumption

Standard Assumption

0.1 to 0.2 (IWC)

365 (W per 1000 cfm)

New Construction Single Family
Air Conditioner

0.41 to 0.50 (IWC)

510 (W per 1000 cfm)

Existing Construction
Single Family
Air Conditioner

0.53 to 0.55 (IWC)

492 to 574 (W per 1000 cfm)

High static pressures produce reduced air flows and the need for higher horsepower fan motors to approach proper flow. Indoor fan motor energy consumption is a result of external static pressure, flow, fan efficiency, motor efficiency, as well as cabinet and heat exchanger design. The standard DOE assumption for indoor fan energy consumption is 365 watts per 1000 cfm. As presented in Table 2, fan motor energy consumption under actual operating conditions averages 511 watts per 1000 cfm, 40% higher than the assumed value. For a five ton air conditioner achieving 2000 cfm of air flow, this is equivalent to a one kilowatt electric resistance heater in the air stream.

The discrepancy between assumed and actual fan watt draw has a number of deleterious effects. First, the total capacity of the air conditioner is diminished from the specification sheet value by approximately 2%. Second, the total unit watt draw is increased by approximately 5%, to give an overall efficiency drop of approximately 7%. Third, the unrealistically low external static pressure assumption promotes use of indoor fan/motor/cabinet designs that often cannot provide the static pressure needed to produce the proper air flow. In negotiating the ISO test procedure, these discrepancies should be addressed.

An implication suggested by these data is that duct distribution systems should be more adequately sized. While the authors champion this goal, reality shows that most residential duct systems are being undersized using duct slide rules with an arbitrary 0.1 IWC/100 ft. input for duct selection without regard for available static pressure, actual duct length, or fittings. While this is not the approved method for sizing, it is the most common method. Preaching improved duct design is important but air moving systems, which meet current and realistic circumstances, are definitely needed.

Equipment performance at low air flow and Correcting Low Air Flow

Air conditioners are generally designed to have an air flow rate of about 400 cfm per ton across the inside coil. For 3.5- to 4-ton units, the air flow rate should range from 1400 to 1600 cfm. As documented in Table 1, the units tested in these studies did not achieve the design airflow rate even in new construction and even in new townhomes with minimal ductwork.

Low air flow across the inside coil has adverse effects on unit performance. It lowers evaporator temperatures, reduces total capacity, increases latent capacity, and lowers sensible capacity. These effects have been measured in laboratory situations including, Parker et al. 1997, and Proctor et al. 1996b.

The effects of low air flow on unit capacity must be carefully considered, both on a gross basis (without fan motor heat and watt draw) and a net basis (with fan motor effects). Correction of low air flow needs to take into account the fan motor and external static pressure effects. This is illustrated in Table 3.

Table 3. Air Conditioner Performance with Degraded Air Flow

Test Case

Air Flow (cfm/ton)


Percentage increase in EER per 10% increase in air flow
(from next lower air flow test)


Gross Total

Net Sensible (constant static pressure)

Net Sensible (constant duct restriction)

Gross Total

Net Sensible (constant static pressure)

Net Sensible (constant duct restriction)

Proctor (Proctor et al., 1996b)

Avg. 3 Tests








Avg. 3 Tests





Parker (Parker et. al., 1997)













































When low air flow is corrected, the gross total capacity increases as the air flow increases. This is due in part to higher evaporator temperature. When the air flow is increased and duct sizing is increased sufficiently to maintain the same external static pressure, the net sensible efficiency is also increased. However if the same duct system is maintained on the air conditioner, the net efficiencies (both total and sensible) drop in cases where the initial air flow is greater than the base test (the test with 500 watts per 1000 cfm). This is due to fan watt draws that increase approximately as the cube of the air flow (for a constant restriction to air flow).


Reporting on their studies of Canadian furnace performance, CMHC researchers in 1992 observed that a systems approach was needed for optimizing the performance of space conditioning equipment. They concluded their study by issuing a challenge to the industry: "Nobody is looking at the big picture: how can we match the furnace heat exchanger, blower compartment, motor, blower, and controls so as to achieve optimum space heating and ventilation?"

The nine field tests of both U.S. air conditioning and Canadian heating systems reported here substantiate the severity of air handler inefficiencies and emphasize the need for continued improvement of air handler devices within the framework of the entire HVAC system. The tests also quantify the inaccuracies in standard assumptions used when rating residential air conditioners and estimating the demand impacts. The discrepancies between assumed and actual air hander performance are masking the industry’s need to improve the efficiency of this equipment and causing higher than estimated customer energy costs.

Manufacturers aiming to remedy these problems may find the benefit through reconfiguring HVAC cabinets and heat exchangers, which control the entrance and discharge conditions of the fan. Performance of fans and motors can also be addressed. While a piecemeal approach holds promise for some improvements, the greatest gains would come through the structurally more difficult whole system approach that includes all these items plus the duct system and the refrigerant circuit.

Design improvements should consider the collective impact of each component’s performance on the whole system. Absent that consideration, air handling devices will not necessarily have the ability to keep up with other system improvements, such as high-efficiency filters now entering the market.


This work was sponsored in parts by Arizona Public Service, Nevada Power, Electric Power Research Institute, Southern California Edison, Public Service Electric and Gas, and Pacific Gas and Electric. Conservation Services Group provided the experienced technicians for portions of the field testing. The work of Florida Energy was sponsored by the Florida Energy Office. Field and laboratory measurements were made by John Sherwin, Rich Raustad and Don Shirey.


ASHRAE. 1999. ASHRAE Standard 62.2P Ventilation for Acceptable Indoor Air Quality. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Blasnik, M., J.P. Proctor, T.D. Downey, J. Sundal, and G. Peterson. 1995a. Assessment of HVAC installations in new homes in Nevada Power Company’s service territory. Research Project 3841-03, Final Report. Palo Alto: Electric Power Research Institute, Inc. TR-105309.

Blasnik, M., J.P. Proctor, T.D. Downey, J. Sundal, and G. Peterson. 1995b. Assessment of HVAC installations in new homes in Southern California Edison’s service territory. Research Project Final Report. San Dimas, CA: Southern California Edison.

Blasnik, M., T.D. Downey, J.P. Proctor, and G. Peterson. 1996. Assessment of HVAC installations in new homes in APS service territory. Research Project Final Report. Phoenix: Arizona Public Service Company, Inc.

CMHC, 1992. "Barriers to the Use of Energy Efficient Residential Ventilation Devices, A Survey of Industry Opinion, and A Review of Strategies for Change". Prepared by Sheltair Scientific, Ltd. for Canada Mortgage and Housing Corporation, Ottawa, Ontario, Canada.

CMHC, 1993. "Efficient and Effective Residential Air Handling Devices," Final Report. Prepared by Allen Associates with Browser Technical, Geddes Enterprises, Brian Woods, and Ontario Hydro for Canada Mortgage and Housing Corporation, Ottawa, Ontario, Canada.

Downey, T and J. Proctor. 1998. Investigation of the AC2 Air Conditioner. Final Report. Pacific Gas and Electric Company, Research and Development Department, San Ramon, CA.

Farzad, M. and D. O’Neal. 1988. An evaluation of improper refrigerant charge of a split-system air conditioner with capillary tube expansion. Final Report. College Station, TX: Energy Systems Laboratory, Texas A&M University. ESL/CON/88-1.

Parker, D.S., J.R. Sherwin , R.A. Raustad and D.B. Shirey III. 1997 Impact of Evaporator Coil Air Flow in Residential Air Conditioning Systems. ASHRAE Transactions, Summer Meeting, June 23-July 2, 1997, Boston, MA.

Parker, D.S., 1997 "Measured Air Handler Fan Power and Flow," memorandum to Armin Rudd, Florida Solar Energy Center, October 8, 1997.

Proctor, J.P, M. Blasnik and T.D. Downey. 1995. Southern California Edison Coachella Valley Duct and HVAC Retrofit Efficiency Improvements Pilot Project. Southern California Edison Company, San Dimas, CA

Proctor, J.P. , M. Blasnik T.D. Downey, J. Sundal, and G. Peterson. 1996a. Assessment of HVAC installations in new homes in Nevada Power Company’s Service Territory. 1995 Update, Nevada Power Company, Las Vegas, Nevada.

Proctor, J.P., T.D. Downey, C. Boecker, Z. Katznelson, G. Peterson, and D. O’Neal. 1996b. Investigation of Peak Electric Load Impacts of High SEER Residential HVAC Units. Assembly, Testing, and Investigation of a Reduced Peak Load Air Conditioner. Pacific Gas and Electric Company Research and Development Department, San Ramon, CA.

Presented at:

2000 ACEEE Summer Study on Energy Efficiency in Buildings
August 20-25, 2000
Pacific Grove, CA