AIRFLOW TESTING: 8 Ways to Test Residential HVAC Airflows with Corbett Lunsford

Corbett Lunsford demonstrates 8 methods for airflow testing, including:
1. Exhaust Flow Pan (Energy Conservatory's Flow Meter)
2. Cardboard Box Flow Pan (handmade by Corbett)
3. Pressure Matching (FlowFinder from Retrotec)
4. Pressure Matching (Duc Tester from Retrotec)
5. Velocity Pressure (24" Pitot Tube from Dwyer)
6. Small Vane Anemometer (Testo 416)
7. Large Vane Anemometer (Testo 417)
8. Plastic Bag (30 gallon lightweight garbage bag)

For more on these diagnostics:

[eddykain]

100% legit stuff nicely done. Now why YouTube has failed me by only just now recommending this video is beyond me.

[bialyk]

Great idea with the plastic bags - love it :)
I spent ~50€ on "better" Chinese anemometer/flow meter and this was horrible un-accurate when measure speed (you can watch my struggles on YT). For range 4-30 mph inaccuracy was up to 5%, but under this number even up to 30%. Above 30mph goes again bad, It was hard to estimate, but no less than 10% around 60mph (for this use car and anemometer on pole+GPS).

[frankgall]

been watching your videos for a while now and ordering the book now. hope to hear you on hvac school more often. love what you do

[neilcomparetto]

Not my first time watching this video... still one of my favorites of all time!!

[lakemechanic]

That Retrotec DM32 is quite pricey. Can one calculate flow rate from the box & simple manometer pressure drop & save a grand+? If so, what is the equation?

[jimbergmann]

Corbett,  
Just a few notes/suggestions. The large vane was not used properly or as intended for exhaust fan flow. The vane would be influenced by the rotation of the exhaust fan. There is a flow funnel set made for the vane and a funnel factor that is used when measuring exhaust airflow. In addition, both vanes allow for the input of area to automatically calculate the CFM from the velocity.

Second, the reason the first are lower then the last 4 is the last 4 were measured independent of air density or corrected for air density. The Testo vanes actually measure airflow by measuring the number of rotations of the fan which measures airflow independent of air density. 

The first 4 measurements all measure airflow by measuring the pressure drop across a fixed orifice the fan orifice or a pitot tube array including the powered flow hood. They are all manometers. Air density is affected by barometric pressure, temperature, and relative humidity. I do not believe that any of the instruments you used correct for all 3. 

What you effectively were able to show is that if air density is not considered or corrected for the airflow readings will be lower than normal. Also while the powered flow hood has been touted as the industry standard, the TAB industry still uses the Pitot Tube as the standard for all airflow measurements. 

As the ductwork is rarely accessible when testing exhaust fans, a powered flow hood at the exhaust inlet, a vane with a hood, or the exhaust fan flow meter would be the most effective methods for measuring exhaust. The large vane and the small vane used as demonstrated would not be as accurate. The garbage bag while interesting is not an easy or effective method for most applications. 

Interesting video

Jim 

[GaiaCarney]

‘...whole house mechanical ventilation device...’ That sounds cool 😎

[ucanoe]

Thank you Corbett, excellent video, I would like to know what the proper CFM values are for some house hold appliances…for example I have a range hood that is super noisy and does not seem to draw much air up. Is there a way to test it? and what should a reasonable range hood exhaust CFM be? I can test from the kitchen under the hood or go on a ladder outside and test the output vent?

[petermanoj]

Dear Corbett,
I need to measure air flow in a corrosive channel and it has a temperature measuring from 150oC to 300oC. Can you recommend Fluke or Testo instruments for the same? or give your inputs. Thanks

[brendahiggins]

What if I don’t have option of all this testing equipment?

[ThaylorHarmor]

Great video. Anyone know of a solenoid that will divert airflow between two PVC tubes?

[mclordhelmet]

I'm trying to verify the CFM based on your cardboard box example. I think you said it was reading 10.5 Pa for the pressure. Was 10.5 Pa the velocity pressure?

[bjs]

I understand how you are measuring an exhaust fan CFM but why can't you use this to measure CFM at an AC register? Using Retrotec DM32 and a cardboard box.

[Graham_Wideman]

A collection of methods patiently explained -- nice! Question: After you attached the calibrated downstream fan, you adjusted that fan such that the pressure in the connecting duct was zero in order to get the cfm reading from the resulting calibrated fan setting. OK. But then you left that calib fan attached for all the subsequent tests. I'm pretty sure for all those subsequent tests you could have done them without the calibrated fan in the system, though you might have to make a small adjustment for the air resistance of the short length of duct, right?

[grooveneedle]

can anyone provide the dimensions of the RO(s) of the E1 E2 E3 on the TEC Minneapolis Exhaust Fan Flow Meter. i know there "BOX" IS 13 X 16 X 8. wondering if i had a similar sized "TOTE" could i save $$$ ? im not down with walking around with a pizza box and a garbage bag.. Thanks!!!!

[PaulLadendorf]

Thanks. Great video. What kind of meter are you using for the pitot tube?

[cafedarwin]

I’m setting up a duct for orchid growing and see people use corrugated pvc/aluminum. Will schedule pvc hard pipe (6”) have less turbulence leading to higher cfm down a 12-foot stretch with 400CMF 6” in-line fan? Would a film with dimples adhered to the inner side of pipe cut turbulence at the boundary wall?

[chronic]

Sorry to keep troubling you but also could you tell me what model is the ventilator/fan you are using, trying to recreate your test setup. Thanks

[umuthevaldogantan]

So the Panasonic ventilator is smart and changes its speed depending on the resistance. How can you assure that the ventilator stays at constant cfm with every measurement method. Without the ventilator having a constant cfm I assume you can not compare these measurements because the ventilator will adjust its cfm based on the resistance?

[singhmaster]

Would I be able to use this system to test the air flow for something way more pressured? Like the force of a car or semi truck exhaust? Or can anyone recommend something different?