Measuring airflow is easy… measuring airflow accurately is quite a bit more difficult. In many cases when we as technicians measure airflow we are trying to get to the almighty CFM (Cubic Feet per Minute) volume measurement. You can take CFM readings fairly easily with a hood like the Testo 420 shown above, but even a hood has some limitations when the goal is to measure total system CFM vs. register / grille CFM.
In this series of videos Bill Spohn from Trutech tools demonstrates all of the tools you can use to measure airflow from hot wire and rotating vane anemometers, to flow hoods, to smart grids and pitot tubes, all the way down to using a GARBAGE BAG.
I had the privilege of seeing this presentation in person (I am the one behind the camera) and I wanted to share it with you. It is well worth your time.
Good friend and contributor to HVAC School Neil Comparetto made this video showing the way in which he creates access ports for static pressure and gas combustion analysis. As techs we find ourselves in the tough position of needing to drill access holes to take measurements but the drilling and sealing of the holes can sometimes create real and perceived issues with the equipment. Many techs use high temp RTV Silicone, Rectorseal Duct Seal compound or even tape. In some cases these sealants may be appropriate but Neil shows how he uses plugs to make a good permanent access point. Always make sure to leave any work is a well sealed and workmanlike condition.
You can find many of these items at Trutech tools HERE
In this 60-second tech tip video by Brad Hicks with HVAC in SC. he shows us how and why to remove the weep port plugs on a condensing fan motor. I know from experience that motors can fail prematurely when this practice isn’t followed. Remember that motor orientation dictates which are removed. It (generally) the ports facing down that need to be removed and the ones face up stay in place.
Recovery is the removal of refrigerant from a system to either store and send in for recycling or to reintroduce back into the same system.
Here are some top tips –
We cover all of this and more in this video –
There are many acceptable methods for making a wire splice and you need to consider many different factors when making a splice. Here are a few considerations.
Here are a few options for splicing wires depending on application –
Splicing any high voltage conductor in an “open” manner or in way that is not specifically rated. In most cases get a UL rated connector and make the connection inside a UL / NEMA rated rated box or assembly.
Making a splice by just twisting wires together and putting electrical tape on top. Just don’t.
Using wire nuts and creating a big ball of wires and running electrical tape over them until it looks like a giant blob of tape.
Use wire nuts on low voltage or control wire in dry and accessible conditions but twist them so the wires stay neat and lay half of the conductors in one direction and the other half in the other direction and tape up in a neat fashion.
The same type of configuration with 3M Scotchlok crimp connectors for better moisture resistance than wire nuts.
In some mildly damp conditions you may be able to use self fusing silicone tape for a more water resistant layer than electrical tape.
Use butt end connectors on stranded wire or if using small gauge single conductor wire (like 18ga stat wire) you can double the end of the wire over before making a crimp. When making a crimp ensure that that the actual crimp is made on the side of the connector OPPOSITE the seam. Once you make a butt end connector pull HARD on it totect and ensure that no bare wire is exposed outside of the insulator.
Use heat shrink butt connectors and stagger the connections to reduce the bulge. Heat the connectors to seal them, then run a piece heat shrink over them all. I found this 4:1 shrink ratio, marine grade heat shrink that should do a great job or water proofing. Heat shrink can be a real life saver and you can use a heat gun or a small butane torch to heat it up. Coincidentally they also make little, portable butane soldering irons as well.
When making a soldered splice make sure to use rosin core solder and wipe off the rosin flux before covering the splice to help prevent corrosion. Remember to run the heat shrink over the cable and the individual conductors BEFORE you start making the splices to prevent sadness and yelling.
The best options are to just run a new wire or make the connections inside of a rate box with proper connectors. Sometimes the best way is the simplest way.
In this video we cover the basics of using the Testo 510i with a pitot tube to do a duct traverse and easily calculate Velocity in FPM and volume in CFM on a small 8″ duct. Using this method is handy because you can use the reliable, accurate and inexpensive 510i to perform the measurement without any other equipment other than tubes and a pitot tube.
As stated in the video, a pitot tube is best (most accurately) used in the following conditions –
For more information see the following links –