Condensing Boiler Annual Efficiency

Condensing boilers can achieve thermal efficiencies up to 98%. However, boiler efficiency is highly dependent on the return water temperature of your system and the percentage of the full load capacity that your system operates at. Use this calculator to estimate the mean boiler efficiency of your system given a return water temperature and percent load at different time intervals.

Time Running at (%)
Time Running at (%)
Time Running at (%)
Time Running at (%)
Operating time (hours)
Operating time (hours)
Operating time (hours)
Operating time (hours)
Mean Capacity (%) 0%
Return Water Temperature (°C)
Overall Boiler Efficiency 0%

Replacing Throttling Valve with VFD for Pumps

For many years, it was common practice for a constant-speed centrifugal pump to control the flow of a system with a control valve in the discharge line. This valve controls the flow delivered to the system. The valve takes a pressure drop equal to the difference between the pressure supplied by the pump and the pressure required by the system. However, this method wastes energy by creating an artificial pressure drop in the system and reducing pump efficiency.

A Variable Frequency Drive (VFD) would use only a fraction of pump energy compared to a system using a control valve with the same operating conditions. This calculator estimates the pump energy savings when retrofitting your system with a VFD.

Pump BHP
% Flow
Hours per week
Weeks per year

Throttling Value

Mean Percent Power 0%
Motor Power (kW) 0
Annual Energy (kWh) 0

Variable Frequency Drive

Mean Percent Power 0%
Motor Power (kW) 0
Annual Energy (kWh) 0

Air Side Energy Calculator

Estimate the amount of heating or mechanical cooling that is required to supply conditioned air to a space in a constant volume system. You can also see the impact on outside air usage in a system with an airside economizer.

Total Flow
Return Air Temperature
% Outside Air
Outdoor Air Temperature (°F)
Supply Air Temperature (°F)
Mixed Air Temperature (°F) 0.0
Power (BTU / hr) 0.0
Power (GJ / hr) 0.0
Power (kW) 0.0

Ventilation Cost

A small exhaust fan left running at night can be easily overlooked, but you may be surprised by the energy cost of leaving it on. Use the ventilation calculator to determine the annual energy consumption and cost for heating ventilation air to space temperature.

Natural Gas

Flow (CFM)
Energy (GJ / yr) 0.0
Fuel (GJ / yr) 0.0
Utility Rate ($ / GJ)
Annual Cost ($ / yr) 0.0


% of time System is ON
Flow (CFM)
Consumption (kWh / yr) 0.0
Utility Rate ($ / kWh)
Annual Cost ($ / yr) 0.0

Motor Load

What does it cost each year to operate an electric motor? With the motor load calculator you can quickly estimate annual energy use and cost for any electric motor. The calculator is a versatile energy management tool which accepts measured current, full load amps or rated horsepower inputs.

Calculate From:
Measurable Units
Load Factor
Power Factor
Hours Per Week
Weeks per Year
Electrical Rate ($ / kWh)
Motor Load (kW) 0.0
Consumption (kWh / year) 0.0
Cost ($ / year) 0.0