Definitive Guide to HVAC Conversion: GPM, BTU, CFM, and More.
HVAC engineers need to know the relationships between quantities such as GPM (gallons per minute), BTUs (British Thermal Units), CFM (cubic feet per minute), and MPH-Miles per hour also known as GPM (gallons per minute) for cooling towers, waste water treatment, and heating transfer. Instead, their goals are to provide a solid foundation for determining how these various measurements are relationships in reality.
HVAC Conversion Calculator
GPM to BTU/min Conversion:
To convert GPM to BTU/min, the formula is:
BTU/min=GPM×ΔT×8.33
Where:
GPM = Gallons per minute of water flow.
ΔT = Temperature difference in °F.
8.33 = Pounds of water per gallon.
Example:
If water flows at 10 GPM with a temperature rise of 10°F:
BTU/min=10×10×8.33=833BTU/min
BTU to GPM Conversion:
To convert BTU to GPM, rearrange the above formula:
GPM= BTU/min divided by ΔT×8.33
Example:
If the heat transfer is 2,000 BTU/min and the temperature difference is 20°F:
GPM= 2000 divided by 20×8.33 = 12GPM
How Many BTU per GPM?
For a 1°F temperature rise, 1 GPM equals approximately 500 BTU/hour.
GPM to BTU Formula:
The standard formula to calculate BTU per hour from GPM is:
BTU/hr=GPM×ΔT×500
This is derived by converting minutes to hours and incorporating water's specific heat capacity.
CFM to BTU Calculator for HVAC
CFM and BTU are closely related when designing HVAC systems.
BTU/hr=CFM×ΔT×1.08
Where:
CFM = Cubic feet per minute of air flow.
ΔT = Temperature difference in °F.
1.08 = Air's specific heat constant.
Example:
For a flow rate of 1,000 CFM and a temperature rise of 20°F:
BTU/hr=1000×20×1.08=21,600BTU/hr
How Many CFM Per BTU?
The general rule of thumb in HVAC systems is:
400 CFM per 12,000 BTU/hr (1 ton of cooling).
Example:
For an 18,000 BTU system:
CFM= 18000 divided by 12000 and multiplied by 400=600CFM
CFM to BTU:
Converting CFM to BTU depends on the temperature change:
BTU/hr=CFM×ΔT×1.08
For 1,000 CFM and a 15°F temperature rise:
BTU/hr=1000×15×1.08=16,200BTU/hr
CFM to MPH Conversion:
Converting CFM to MPH depends on the duct’s cross-sectional area:
MPH= CFM×0.0024 divided by Area (ft sq.)
Where:
Area = Cross-sectional area of the duct in square feet.
Example:
If the airflow is 1,000 CFM in a duct with a cross-sectional area of 2 square feet:
MPH= 1000×0.0024 divided by 2=1.2MPH
MPH to CFM Conversion:
Reversing the formula:
CFM= MPH ×Area (ft sq.) divided by 0.0024
Example:
For an airflow speed of 2 MPH in a 3 square foot duct:
CFM= 2×3 divided by 0.0024 =2,500CFM
Conversion Charts
Here are quick references for common conversions:
GPM to BTU Conversion Chart
CFM to BTU/hr Conversion Chart
FAQs
How Do You Convert BTU to GPM?
Use the formula:
GPM= BTU/hr divided by ΔT×500
How Many BTU per GPM?
For every 1°F temperature rise, 1 GPM equals 500 BTU/hour.
How Many CFM per BTU?
Approximately 400 CFM per 12,000 BTU/hr.
How to Convert CFM to BTU/hr?
Use the formula:
BTU/hr=CFM×ΔT×1.08
You will be able to calculate and optimize the performance of your HVAC systems efficiently if you understand these key relationships and formulas. Apply them to better energy efficiency and cost savings in your heating and cooling solutions.
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