Hello all,
I’m studying for the national exam, and the material/books that I have contain different ranges for acceptable temp differential between supply and return. For testing purposes, I need to be able to determine if it’s 15-20, 14-20, 14-22, etc. Does anyone know where I can get a definitive answer from?
Are you required in your jurisdiction to report the difference between the air temperature going into a return and the air temperature coming out of the supply?
Yes, based on the Texas SOP it’s supposed to be between 15 and 22. But I’m not sure what the limits are in regards to the national exam.
I don’t recall seeing that question when I took the national exam. I typically like to see between 15°F and 20°F depending on outdoor temperature and humidity levels.
If I am not mistaken the term is Delta T or Split Temp between supply and return.
15-20. The supply side should be cooler.
I use 7 degrees.
Wait for others to reply.
The answer is “Between a lick and a promise”.
I see you’re going for your Texas license. Have fun in your inspecting career here in Texas!
You use 7 degrees for what?
Split Temp degree spread. 15 - 22.
You use a 7 degree delta t for deciding if the AC is working properly?
No. I was not paying attention.
Thank you for that.
That should be included in a few MB poster’s signature.
Fair question; however, I do not believe the NHIE will ask you to know those ranges because they are arbitrary.
The answer will be: The ranges vary based on environmental conditions and on the characteristics of each individual system.
(For the record, this is one of several reasons why I think TREC has it wrong in requiring HI’s report on such an arbitrary subject)
Not to mention, high likelihood that you are not measuring temps correctly. Most just point their IR.
The Texas requirement is absurd as has been pointed out by many over the years. I’ve heard a vast range of splits over the years. Partly because it is subjective, and mostly because there are several factors involved in recognizing applicable splits. For testing purposes, go with what they say and pass the ridiculous test.
The Texas requirements are as follows from the Rules.
the inspector shall:
measure and report the temperature difference between the supply air and the returned air or report industry-accepted method used to determine performance;
the inspector shall report as Deficient:
deficiencies in the performance of the cooling system that:
fails to achieve a 15 degrees Fahrenheit to 22 degrees Fahrenheit temperature differential;
or fails to cool adequately as determined by other industry-accepted methods
We already know that reading DT at the supply and return registers is not an accurate method and can vary significantly from measuring at the air handler itself. As Inspectors we are also not required to perform any destructive testing of any kind. That would include punching holes in a supply and return plenums or ductwork at the unit to use a thermostat there.
In addition to that we are not required to use a ladder inside of the home for any reason. Most homes these days are using 9’ - 10’ ceilings. Many also have returns in every bedroom at the same heights. So how do you get a thermostat into the register without contacting the register and reading its temp and not the air temp? So that leaves them pointing their thermometer at the registers from 10’+ away and taking bad readings.
The industry accepted methods to check the performance of a unit go way beyond what an Inspector without an HVAC license can do. As a result the Inspector is basically relegated to either using their temperature measuring equipment (IR is not required) to perform an inaccurate assessment of the performance of the system.
Yes the rules are hosed here and is why I said the following to the OP. This one item is by no means the other fun the OP faces.
Please correct me if I’m wrong. I generally use an IR thermometer (Fluke) and check temps at all registers and the return. I’m just try to verify that the system works satisfactorily and if there might be issues with particular ducts (I.e. a temp that is extremely irregular in comparison with the other registers). I know it’s not exact, but believe it gives an acceptable evaluation of a system’s health.
Thanks!
In my opinion, if you understand your area and the equipment, you can make a generalized assessment and suggest action. Other clues, such as the system unable to meet thermostat demand, elevated humidity, age and care of the system, etc. all contribute to the overall evaluation. But running in there and reporting some arbitrary measurements is not helping anyone.
For example: I have concerns the AC is not cooling adequately or efficiently because I observed x, y, and z. Recommend service and corrections or repairs as needed…
Not trying to beat up on you so don’t take it wrong. However define “satisfactorily” and “acceptable” with regards to the proper operation of the system? Even expecting that you are reading the actual air temperature and not surrounding materials how do you know that the system is not capable of pushing better temperature outputs? How do you know that (one example but not the only one) the fan in the air handler is operating at a proper speed? Keep in mind if in the cooling mode it is operating to fast it may not draw off humidity from the air as it may be designed to do and as may be expected with a properly set fan speed.
In CA it is the age of unit, older units 14-22 or 15-22, Newer units are 18-27 ( as an example) so it varies in requirements per age of unit. Tough to have a 25 year old AC compressor meet same requirements of the Behemoth AC units they have now. Hey if my bald head gets cold while standing under register were good. 
