View pricing, availability, product information and place orders online 24/7 at singlesource.mingledorffs.com

Measuring Airflow Using Temperature Rise Method

Bubba Moore

Bubba Moore

Technical Services Manager
Southeast District

Measuring Airflow Using Temperature Rise Method

What is airflow in a heating and cooling system? Why do we need to know what the airflow of a heating or cooling system is? Airflow is the amount of air measured in cubic feet per minute (CFM) that a system can deliver or move depending on its size. This CFM of a system is normally around 400 to 450 CFMs per ton of air. This can vary depending on the efficiency of the system. The reason we need to know the airflow of the system is to make sure that the system is performing as it was designed. Too much or too little airflow can affect comfort and cause equipment failures.

There are different methods of measuring airflow. The temperature rise method is fairly easy to use when measuring the CFMs on fan coils with electric heat. You will measure the amount of temperature rise across the electric heat elements, and also measure the voltage supplying the system, as well as the current flow or amps of the fan coil. The fan coil blower and electric elements will have to run continuously while preforming these measurements. Before taking any temperature readings or other measurements, make sure that the air filter is clean, and that all supply and return vents are opened and not blocked. Also, let the system run until the temperatures stabilize. Once the temperatures stabilize, measure the return air and supply air temperatures with an accurate electronic thermometer.  Do not get your temperature reading above the electric elements. Make sure that these readings are down the duct or out of the line of sight of the electric elements.

HVAC and Plumbing Distributor

After the measurements have been gathered, this data will be plugged into a formula to see what airflow (CFMs) the system is producing. The formula is: Airflow (CFM) equals volts times amps times 3.414 (BTUs per watt) divided by 1.08 times the temperature difference of the supply and return air.

HVAC and Plumbing Distributor

Using 400 CFMs per ton, this airflow calculation would be close to 3 Tons of airflow.

HVAC and Plumbing Distributor

This simple calculation could help prove whether or not the problem is related to airflow. There may be a collapsed duct, or insulation inside of the duct may have come loose. If there was an equipment failure, this CFM test could prove why the equipment failed. It could also prove that airflow was not the problem and help point to a different reason for the failure.

Sources: HVAC Services Procedures

More to explore

Native American Heritage Month

November is Native American Heritage Month November represents a time to celebrate the rich cultures and traditions as well as acknowledge the

Because I was Inverted

For this article, I will explain how to replace the main control board on a 38MARB ductless outdoor unit. The boards are

coil cleaner

Cleaning Coils

Fall is the time for the leaves to fall and with the mixture of rain and wind tends to stir up debris

Keep up to date with the latest HVAC news from Mingledorff’s Inc.

Alabama Locations

Anniston (256) 241-3026 105 E D St, Anniston, AL 36201
Auburn (334) 734-8011 2295 1st Ave, Opelika, AL 36801
Birmingham (205) 250-7714 516 31st St N, Birmingham, AL 35203
Dothan (334) 836-1035 205 Wedgewood Dr, Dothan, AL 36303
Gulf Shores (251) 968-2660 820 Commerce Dr, Gulf Shores, AL 36542
Huntsville (256) 859-2691 391 Nick Fitcheard Rd NW, Huntsville, AL 35806
Loxley (251) 964-2707 30020 Co Rd 49, Loxley, AL 36551
Mobile (251) 476-2220 5522 W Commerce Blvd West, Mobile, AL 36619
Montgomery (334) 262-4855 861 Plantation Way, Montgomery, AL 36117
Muscle Shoals (256) 383-6904 107 Commerce St, Muscle Shoals, AL 35661

Georgia Locations

Albany(229) 432-5254205 Baldwin Dr, Albany, GA 31707
Athens(706) 548-2563105 Whitetail Way, Bogart, GA 30622
Atlanta(404) 875-77551290 Tacoma Dr NW, Atlanta, GA 30318
Augusta(706) 651-19503618 Wrightsboro Rd, Augusta, GA 30909
Brunswick(912) 265-5193275 Rose Dr, Brunswick, GA 31520
Columbus(706) 322-38706201 W Hamilton Park Rd, Columbus, GA 31909
Conyers(770) 918-9132335 Gees Mill Business Pkwy NE, Conyers, GA 30013
Forest Park(404) 361-24745158-C Kennedy Rd, Forest Park, GA 30297
Gainesville(770) 297-93352472 Hilton Dr, Gainesville, GA 30501
Lawrenceville(678) 442-10602111 Cedars Rd SE, Lawrenceville, GA 30043
Lithia Springs(770) 948-3451320 Thornton Rd #106, Lithia Springs, GA 30122
Macon(478) 474-85445527 Thomaston Rd, Macon, GA 31220
Marietta(770) 426-05511060 Triad Ct, Marietta, GA 30062
Newnan(770) 239-210570 Enterprise Ct, Newnan, GA 30265
Peachtree Corners(770) 239-21006675 Jones Mill Ct, Peachtree Corners, GA 30092
Savannah(912) 232-1228103 Central Jct Blvd, Savannah, GA 31405
Statesboro(912) 764-8841126 W Parrish St, Statesboro, GA 30458
Valdosta(229) 245-8200363 Connell Rd, Valdosta, GA 31602
Warner Robins(478) 953-3727110 Byrd Way, Warner Robins, GA 31088

South Carolina Locations

Hilton Head(843) 689-34043715, 21 Hunter Rd, Hilton Head Island, SC 29926

Florida Locations

Fort Walton Beach(850) 244-201776 Beal Pkwy SW, Fort Walton Beach, FL 32548
Panama City(850) 913-05853012 Lisenby Ave, Panama City, FL 32405
Pensacola(850) 438-10054405 N. Palafox Street, Pensacola FL 32505

Mississippi Locations

Hattiesburg(601) 579-96701851 Lincoln Rd, Hattiesburg, MS 39402
Ocean Springs(228) 497-5090Sunplex Industrial Park, 5717 Suntec Drive, Ocean Springs, MS 39564

Commercial Sales

Norcross – North Georgia Hub
(800) 282-4911

Birmingham – North Alabama Hub
(205) 250-7714

Macon – Southwest Hub
(800) 342-9250

Loxley – Gulf Coast Hub
(800) 239-7419

Savannah – Southeast Hub
(800) 822-7617

Commercial Parts

 CompanyWeb AddressDescription
Airzonewww.airzoneinc.comCustom and Underfloor Air Handlers
Aladdin Metal Productswww.aladdinmetalproducts.comCurb Adapters and Roof Curbs
Aprilairewww.aprilaire.comIndoor Air Quality Products
Autaniwww.autani.comBuilding Automation and Controls
Bardwww.bardhvac.comHeat Pumps,Gas/Electric, and Wall Mounted Air Conditioners
Bryantwww.bryant.comCommercial, Industrial, Residential Heating & A/C Products and Controls
Carrierwww.commercial.carrier.comCommercial and Residential Heating & A/C Products
Data Airewww.dataaire.comPrecision Air Control for Data Processing Centers
 DXairwww.dxair.comPool dehumidification systems
 First Companywww.firstco.comFan Coil Units
Global Plasma Solutionswww.gpshvac.comAir Purification and Bi-Polar Ionization
 Greewww.greeusa.comPTACs
 Hayes Fluid Controlswww.haysfluidcontrols.comHose Kits and Control Valves
 iAirewww.myiaire.comCommercial Air Purification using ionization with energy savings
 IslandAirewww.islandaire.comPTACs, Vertical Units, Water Source Heat Pumps
 i-Vuwww.commercial.carrier.comBuilding Automation and Controls
 Magic Airewww.magicaire.comFan Coil Units
 Micro Metlwww.micrometl.comRoof Curbs, RTU Accessories, & ERVs
 Modinewww.modine.comGas-Fired Unit Heaters, Duct, Furnaces, Hot Water Cabinet Unit Heaters, Makeup Air, and Dedicated Outdoor Air Systems
 Network Thermostatwww.networkthermostat.comInternet Thermostats, Wifi Themostats, Ethernet Thermostats
Paynewww.payne.comResidential Heating & A/C Products
Rawal Deviceswww.rawal.comContinuous Capacity Modulation and Dehumidification for DX Systems
Renew Airewww.renewaire.comFixed-Plate ERVs
Totalinewww.totaline.comCompressors, Parts, and Supplies
United CoolAirwww.unitedcoolair.comModular All-Indoor HVAC Systems
 Warren Technologywww.warrenhvac.comElectric Heaters
 Wilo Pumpswww.wilo-usa.comPump Systems for HVAC and Water Supply and Sewage