Temperature differential test?

Yep! I use a what I call a needle thermo.
It is easy that way.

Just curious as it appears that TREC believes this is a valid test method and nailed an Inspector on it. Got to love it when the State licensing board jumps in and makes a determination they have no clue about! :roll:

TREC fines Inspector for improper temp split call

Yep! They must be a bunch of dumb f-cks.

In several conversations with my HVAC tech, he has assured my that DeltaT, whether measured at the registers or at the unit, is not an accurate indicator of whether the system is operating properly. Nothing short of a proper analysis by an HVAC tech can determine that conclusively.

However, my clients look to me to give them guidance in this regard, so I resort to the imperfect method of determining DeltaT and then decide whether my findings warrant evaluation by a licensed HVAC tech.

If the unit has been running for ten minutes or more, the thin metal fins of the typical residential registers will be close enough to the temperature of the air passing across them for initial analysis. If I see a DeltaT of at least 14 degrees at the registers (using a non-contact thermometer as in the original post), experience has shown me that I will find at least that (and usually better) if I test at the unit itself. If it is lower than 14 degrees, I will test at the unit (using two calibrated probe-type thermometers). If I am getting less than 15 degrees DeltaT, I note it on my report and refer the client to an HVAC tech. Most of the year in Texas, attic temps are higher than living space temps, so there is almost always temperature gain in the ductwork during cooling season.

Those who say DeltaT is not an accurate indicator of proper AC performance are correct, but in the absence of testing that a home inspector can reasonably perform, it’s the best we can do.

Or is it? Does anyone feel they have a better way of determining, through objective means, the performance of an HVAC system?

Wrong test and wrong tools for the test. …

Where did you come up with the 14 and 15 numbers above? What if the difference is 30+?

For as long as I can remember, 14 degrees has been the number that has been bandied about as the “acceptable” DeltaT for cooling systems. I know it does not appear in the TREC SOP. I find that the vast majority of properly functioning and maintained units can deliver at least 15 degrees DeltaT or better when measured at the unit. When I see lower than that, I think it’s a wise move on my part to have a tech look at it. I know I run the risk of having someone out without there being an actual issue, but better that than being too lax and having a client with an AC that isn’t performing.

If I see the DeltaT as high as 22 degrees in cooling mode, I call it out, as it is my understanding that this can indicate one or more of several issues with the unit.

For heating, I look for at least 25 degrees temperature rise. It’s rare that a unit fails to do that, and it is almost always an electric furnace that fails in this regard.

Occasionally I come across a heater putting out over 140 degrees. When temperatures are that high I worry about air flow and ability to maintain even temperature during the heating season and call it out. Again, I would rather risk being overly cautious for the rare instances it comes up than passing it by and having a disgruntled or, God forbid, dead client.

I employ these standards for the sake of consistency and accountability. This way, if someone asks what I consider “acceptable”, I have an answer for them. Also, it is my understanding that consistency of approach is very important when it comes to defending oneself against a claim with TREC. Standards also provide a way for me to separate out what might be causing a home to be difficult to heat or cool. If the DeltaT is within “acceptable parameters”, I tend to rule out the HVAC unit and look to insulation, ducting, weather seals or, in some instances, cooling/heating capacity of the unit(s) involved.

I realize that these are arbitrary numbers and that they are of little use when it comes to determining what, if anything, is deficient in an HVAC unit. Like I said, if someone has a better approach, I am always open to persuasion. I have to say that I would not be comfortable with the “It was cooling/heating fine” approach. I think that would leave me open to accusations of being arbitrary and/or inconsistent in my approach.

I’ve curiously watched the responses anytime someone brings up HVAC testing as it seems to me there are about 104 different ways to test…depending on who you talk to. Seems to be one of the few things no one can agree on.

If he got a good differential using that method, wouldn’t you think it would be even greater if measured at the unit by inserting a thermometer? Performing an exact measurement is beyond the scope of a home inspection. I do exactly what he did but I don’t mention differential unless it is low.

A test a HI inspector goes through is a bare bones , without proper gauges and hour testing , you not testing for proper the operation . You can say it is operating or it is not . Carry on boys . Taking temperatures and Humidity is about all we can do .

I’m prefacing this by saying I know little about this testing but am reading this thread for my own edification. I was involved in a home sale a year ago and the HI report stated this:

When the unit cover was removed this was found, was there no value in this testing?

There you go!

With nasty coils wouldn’t that cause a low measurement due to the air cannot be fully cooled.

Why would it not be cooled?

You are slowing down the air across the coil.

Reduced air flow causes lower evaporator temps.

Inspectors don’t know how, where and with what to do this test, then don’t know what the test results means?

Is the suction refrigerant line warmer or cooler with a dirty coil?

If you have a dirty evap. coil, would the blower motor amp draw be higher or lower?

What effect does the bypass factor have on SA Temps?

If this makes no sense, there is no sense in trying to do this test because you do not understand the test results.

Your job is to see if it runs, not how well it runs. Why not leave it at that?

Maybe so, maybe no. I was trying to get the AC in an investment property to perform up-to-par and and found that the coils were clogged with dirt, dust, what-have-you. I would have thought that cleaning them up (as I did) would gain me another 2-4 Delta T degrees Delta T, but I barely gained 1.

I could imaging a scenario in which the flow across the coils was attenuated, but the actual amount of cooling surface was not greatly affected. If there was that much gunk on the coils, I also wonder what the filter looked like.

What about air pressure differential?