Heat power calculator

for heaters and chillers

online since 2005

Registration and subscription

Select a subscription plan and enable the full service:

  • Switch between metric and imperial units in one click
  • Export calculation results in Word .docx or Excel .xlsx format
  • Preview results on one place and copy/paste it in your favorite text editor
  • Send results back to your email
  • Support the future of this project

And even more... Subscribed users have access to the full set of 19 calculators available as Java™ Web start application or download Windows™ 64bit application.

Select the annual subscription and enable full service for only 0.05 USD/day Subscribe

Annual subscription

from $0.05 / day

total cost for one year $18.25

Calculation setup
Flow rates and heat power
Diameter and velocity
Fluid properties

Exclusive calculator

On exclusive calculator page you can use the online calculator without interference from advertisements, additional text, links and other content that is not required for the calculations themselves. A pure experience of using a calculator as with a desktop application.

An exclusive version of the calculator is available to registered users. Choose the right subscription duration and start using the exclusive service.


Calculator description

Read more about calculator application and check if calculator is suitable for your problem.

Also, read about calculation procedures, what you have to know for the calculations and what limitations apply.


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If you need a quick calculation, but you are not still familiar how to use the calculator, you can order calculation service from the calculator developer.

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Available in download version

save/open results
export to word and excel
print results
custom fluid properties
K factor for fittings, resistance coefficient
compressible isothermal flow
dry air isothermal flow
gas discharge flow
natural gas flow


Calculator start selection

Read all about available deployments. In any way of utilizing calculator, Internet connection is required, for authentication at least.

Issues and answers

Having problems with calculators usage? Read more about known issues and problems and way to solve it.

issues and answers


P - heat power
Heat energy in the unit of time exchanged in the device.
q - volume flow
Volume flow rate of the fluid at actual pressure and temperature.
ṁ - mass flow rate
Fluid flow rate in terms of units of mass per unit of time
T1 - inlet temperature
Fluid temperature in front of the heat exchanger
T2 - outlet temperature
Fluid temperature after the heat exchanger
ΔT - temperature change
Fluid temperature difference before and after the heat exchanger. Gained or lost temperature depending if the device is a heater or a chiller
ρ - fluid density
Actual fluid density in terms of mass per unit of volume on real pressure and the temperature
C - specific heat
Heat capacity (specific heat) of the fluid; Specific heat at constant pressure for a gas, in terms of energy per unit of mass and temperature.
D - diameter of tube
Internal pipe diameter
V - flow velocity
Fluid flow velocity in the pipe of the heat exchanger

Calculation setup

Select calculation type
Calculate heat power for known flow rate
q / ṁ
Calculate flow rate for known heat power
Select value to input. You should enter selected one. The other one will be calculated
volume flow rate
mass flow rate
Select value to input. You should enter selected one. The other one will be calculated
temperature after the heater/chiller
temperature difference in the device
Select value to input. You should enter selected one. The other one will be calculated
internal pipe diameter
fluid velocity
Select device type
Device that has outlet temperature lower then inlet one, due to heat energy released from the fluid to the surrounding one
Device that has outlet temperature higher then inlet one, due to heat energy of the fluid increased and surrounding fluid chilled

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