To allow facility managers and engineers to quantifiably estimate the total financial impact of delayed filter maintenance
Filter Type
MERV (Efficiency) 

Filter Manufacturer / Model 

Filter Price (each) 
$

Number of Filters in Bank or Building 

Filter Initial Resistance ("wg) 

Recommended Final Resistance ("wg) 

System Airflow (cfm) 

Operating Days / Year (system) 

Hours Operated / Day 

Energy Cost ($/kWh) 
$

CO2 Emission Rate (lbs CO2/kWh) 

Drive Efficiency % 

Motor Efficiency % 

Fan Efficiency % 

Typical Filter Change Frequency (months) 

Proposed Filter Change Frequency (months) 

Annual Filtration Cost for System with Routine Maintenance
Filter Cost  $0 
Energy Cost  $0 
Total Cost  $0 
kWh Consumed  0 
CO2 Emissions (tons)  0 tons 
Annual Filtration Cost for System with Delayed Maintenance
Filter Cost  $0 
Energy Cost  $0 
Total Cost  $0 
kWh Consumed  0 
CO2 Emissions (tons)  0 tons 
Cost of Delayed Maintenance
Filter Cost  $0  Filter Cost Savings 
Energy Cost  $0  Increased Energy Cost 
Total Cost  $0  Decreased Total Cost 
kWh Consumed  0  Increased Energy Consumption 
CO2 Emissions (tons)  0  Increased CO2 Emissions 
Calculation Assumptions
Filter pressure drop is calculated as the straight line average between the initial pressure drop and the final pressure drop.
The relationship between airflow resistance and energy is captured in the calculation below
This calculator is based solely on the fan energy to move air through the filter system, so it applies directly to variable frequency drive systems only.
No effort has been made to calculate the cost to condition (heat or cool) the air flowing through the system In simple systems the run time (which equates to energy) is determined by the systems ability to bring room temperature to setpoint.
Typical values have been used for drive efficiency, motor efficiency, and fan efficiency as determined by the National Air Filtration Association. These values may be changed to reflect the design and capability of your system.
CO2 emissions are calculated from increase in energy consumption which drives production of electricity, based on EIA/DOE published values of CO2 emissions per kilowatt hour of electricity produced.
Basic Theory
Filters create airflow resistance within the HVAC system due to the drag of air flowing through the filter fibers.
Filters increase in airflow resistance as they capture airborne contaminants and drag increases. Filter manufacturers publish the initial and recommended final airflow resistance of their filters. These values, typically reported in inches of water gauge, are reported in filter literature.
The energy required to move air through a filter is directly related to its airflow resistance. ASHRAE and NAFA have published an equation to calculate energy consumption based on this resistance. This model is based on that equation (see above).
A new filter will require less energy to move air through it than a filter that has reached it's final airflow resistance.
This calculator assumes that the routine maintenance period entered by the user spans the duration from installation until the filter reaches it's final airflow resistance.
This model calculates the difference in duration between routine and delayed filter maintenance and assumes that the filters being modeled are running at their final airflow resistance during this period. It allows the user to calculate the total cost/benefit of delaying filter purchases vs the extra energy required to operate the dirty filters.