Originally Posted By: hspinnler This post was automatically imported from our archived forum.
I received a call this afternoon from an HVAC tech wanting to vent about home inspectors writing up low Delta T’s using laser temp guns instead of checking with temperature probes in the evaporator coil and return plenum.
He had to go out and service a little old lady and was upset that he had to charge her for the visit. I checked with the Ray-Temp mini after about 30 minutes of running the air at 65 degrees, (it was between 85-90 degrees F outside), the Delta on one side of the home averaged 6 degrees with 10 on the other. He said he checked with his Cooper and found it to be at 20 degrees, which was fine. He gets calls all the time as a result of home inspector's findings. Maybe he should take his company's name off of the covers on the programmable thermostats.
I'm not a former HVAC person like many of you are. This test goes above and beyond the SoP. So, who takes the time to drill, probe and check? Who considers the method I used to check unacceptable? If so, what recommendations does anyone care to pass on in order to do this correctly with the utmost efficiency?
Originally Posted By: jbushart This post was automatically imported from our archived forum.
If your noninvasive test indicated the possibility of a problem and you recommended further evaluation by a trained technician who would, with an invasive measure, make a closer determination to recommend any applicable remedy, there is no problem IMO.
Remember that your temp gun is measuring the surface temp of the grill/duct vent and not the actual air coming from it or going in it, however.
Originally Posted By: hspinnler This post was automatically imported from our archived forum.
Thanks James. Yes, that was one of his arguments. I am checking the surface temperature on flex duct that was in an attic that was over 100 degrees. I see his point. Those duct runs are usually too long anyway.
I may change my tack and look for other signs such as refrigerant line not getting cold, dirty filters, lack of service stickers, and do a general check for my benefit, without reporting the actual numbers.
Originally Posted By: dandersen This post was automatically imported from our archived forum.
Quote:
I received a call this afternoon from an HVAC tech wanting to vent about home inspectors writing up low Delta T's
You'r lucky that is all that you got. You could have gotten the bill!
Quote:
Remember that your temp gun is measuring the temp of the grill/duct vent and not the actual air coming from it or going in it, however
Thank you JB.
Even though the temp gun is a great tool, it is not the tool for the job.
It can NOT be done.
If you review my inflamed posts on this HVAC area you may realize that ANY Dry Bulb test of temp differential is no reason to EVER recommend further evaluation by a competent HVAC contractor.
I just left an inspection (3 times that of most monster houses I inspect). The listing agent was present (required by the seller for all who enter the house for any reason). She asked me about a home inspector who measured temperature differential and the HVAC contractor came and found "all is well". The results of the conversation was, "the bill goes to the Home Inspector"! Hope it was no one here.
Are you reading this stuff Mr. Cook Sr?
If you take the time to research the Laws of Thermodynamics, (you know know, the laws of physics that governed the creation of the universe, unlikely to ever change in our lifetime) it is quite clear that evaluation of an HVAC unit can not now or ever be archived with dry bulb thermometer measurement.
If you use this method of evaluation, I recommend that unless you wish to pay the bill, stop this unnecessary reporting and stick to Home Inspection SOP.
Originally Posted By: hspinnler This post was automatically imported from our archived forum.
Yes David, you are right. The house was 3 years old and no service stickers were observed. The HVAC tech agrees with me regarding recommending annual service. Can you recommend an instrument to use in my inspection should the system be found to not be producing what feels like adequate cooling? I will seek out a local friendly tech to see if he can educate me during startup phase of equipment.
Originally Posted By: jbushart This post was automatically imported from our archived forum.
Roy/David,
I don't know the full history of your discussion, but I know that any deviation from the SOP leaves an inspector at risk. Sometimes you would think that by doing MORE than required, you are MORE protected - but not so.
"If you went beyond what the SOP required for this, why did you not do the same for that and, thus, catch the fact that there was mold in the padding under the carpeting?"
For protection, less is more, as long as your inspection covers all of the standards of practice, IMO.
Originally Posted By: dandersen This post was automatically imported from our archived forum.
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Can you recommend an instrument to use in my inspection should the system be found to not be producing what feels like adequate cooling?
Yes I can. You need a sling psychrometer or an electronic hygrometer that will give you the wet bulb, dry bulb, dew point, relative humidity.
You take readings after the unit has been operating and stabilized (several on/off cycles), then you get a psychometric chart for "standard air" and plot the readings. Then you will need a little help in reading the results. You can determine all kinds of things from here. The btu/hr performance the unit is producing, efficiency loss from the attic being too hot if the ac and duct is up there, gallons of water that will be produced, the latent/sensible heat ratio the unit is working on, bypass factor of the evap coil )how much of the air is effected as it passes through the coil), and so on.
It is very unlikely that all this work and information will mean a whole lot to the client and the mechanical contractor will not know what you are talking about nine times out of ten. So, I am not here to promote HI's to do this stuff.
The best tool is a set of refrigeration gages and good knowledge of how the HVAC equipment works. This will tell you if the unit is "working".
However, the use of a set of refrigeration gages require EPA certification which also may not be of any use to you as a HI.
It is not our job to determine if the unit is the right size for the house. This is arbitrary. You can have a working unit that you will not be "comfortable" in the house. This feeling of comfort is not a determination if the unit is "working".
Originally Posted By: hspinnler This post was automatically imported from our archived forum.
David: I don’t want to go too far overboard with this. My main interest would be in directly checking the air temp at the coil and returns to see if the system is hitting, what is it?, 19 degrees or so.
Originally Posted By: bkelly2 This post was automatically imported from our archived forum.
I use an infared thermometer and look for a split of 18 to 22 degrees F. Never had any problems telling anyone to have the AC checked because the split was too low. Some times I have to determine which is the vent closest to the unit to get a correct reading.
– “I used to be disgusted, Now I try to Be amused”-Elvis Costello
Originally Posted By: cmccann This post was automatically imported from our archived forum.
Mr Anderson,
If you point your thermometer at a supply register and read 68' and the return reads 73' would you just blow it off because it's not a legitimate test, or would you call it out?
Or are you saying you use your hand as a test for cool air?
Originally Posted By: bkelly2 This post was automatically imported from our archived forum.
cmccann wrote:
Mr Anderson,
If you point your thermometer at a supply register and read 68' and the return reads 73' would you just blow it off because it's not a legitimate test, or would you call it out?
Now you are stirring it up. 
-- "I used to be disgusted, Now I try to Be amused"-Elvis Costello
