Zone System Temp Differentials

[Mike W. Cole]

One of the Inspect points that we use for heat pumps and air conditioning systems is to measure the differential temperature between the supply and return air in the system and typically if we see 14-20 degrees we consider the unit working OK if the other points are also OK.
We had a home yesterday with two levels and one system serving two zones in the home. The differential was only 8 degrees and the builder asked if we had run both zones at the same time. I said we had and his comment was that that was normal to see a lower differential with both zones operating.
Anyone had experience with this and is there a differential temp we could use in this situation? Should an effort be made to shut one zone off and take measurements then?

[mnahrgang]

I don't buy it, but I don't know everything...

8 degrees differential, says something isn't right. It could be the units are running just fine, but something else is up and needs to be addressed. (or in all fairness, it could be the builder is right.)

My recommendation to my client would be to have their own HVAC expert come in to evaluate the system independent of what the builder says, and go with their recommendation. It may cost a few dollars, but if something is wrong, now is the time to get it addressed.

[Chuck Evans]

Calling David A... calling David A... Please report to the HVAC thread

Curious, was the system equipped with a barometric bypass damper? That will definitely affect the split when only one zone is running.

The system should be sized to adequately cool the whole house, but you can't go by Delta T alone. So how did the system do at cooling the house? How was the temp of the suction line at the condenser? I'm sure it wasn't cooling well, but don't base your assertion just on Delta-T.

If you don't think it was cooling adequately stick to the report comment. I frequently find systems in new construction that don't cool well because the A/C installer didn't take the time to properly charge it (new construction factory assembly line mentality). The guys who do the callbacks are usually more conscientious and spend the time with the gauges to get the charge right, at least in my experience.

[Brian E. Kelly]

Call it out, let the Builder put his "Story" in writing as well.

8 degrees is not enough, at least here...

[Mike W. Cole]

This system had motorized dampers that controlled the major duct for each level. We have noticed that our rule of thumb ie, 600-700 sqft per ton out of the ground and 800-1000 sqft per ton below grade on zone systems seems to run a little light on tonnage on the zone systems. I would suppose that the design would assume both thermostats would not be calling for heat/cool at the same time at least in most situations and they are able to use less tonnage versus a non-zone system. Other than to 'feel' the suction line we don't measure temps there. Maybe we should. Is there a temp to use for this? 'How well it is cooling the house' is hard for me to define given all the variables that are usually present. This was a vacant home that had the system turned way up when we arrived.
I did in fact recommend analysis by a HVAC person but it was one of those where I thought I could do a better job if I faced this situation at some other date with a more definitive measurement. Thanks you all of you who have responded to date!!

[David A. Andersen]

Anyone had experience with this and is there a differential temp we could use in this situation?

Yea, call it out.

Do you even know anything about a zoned system?

Are you EPA certified to mess with ozone depleting refrigerants?
You do know that this is not just a federal law but international?!

I just inspected a house owned by a ****ing home Inspector. He is trying to sue me.

This idiot is barking up the wrong tree.

If you don't now HVAC, line your *** up and get sued or shut up about what your not required to do.

If you want to make a wild *** guess, go for it and don't bother us about your sorry *** being sued for making the wrong call.

Sorry, I'm not in a ****ing good mood today! ...

[Wayne B. Wilson]

Wow David , Was it Sean's hose lol

[David A. Andersen]

No, but.....

[Wayne B. Wilson]

I meant house lol
You know that little Deal Killer over here.

[Mike W. Cole]

David Anderson,
I know enough to not get sued unlike some other obnoxious home inspectors who are permeating the message center here at NACHI. And please feel free to take that the wrong way.

[David A. Andersen]

Well when you figure it all out, teach us...

[Brian E. Kelly]

Originally Posted by dandersen

Yea, call it out.

Do you even know anything about a zoned system?

Are you EPA certified to mess with ozone depleting refrigerants?
You do know that this is not just a federal law but international?!

I just inspected a house owned by a ****ing home Inspector. He is trying to sue me.

This idiot is barking up the wrong tree.

If you don't now HVAC, line your *** up and get sued or shut up about what your not required to do.

If you want to make a wild *** guess, go for it and don't bother us about your sorry *** being sued for making the wrong call.

Sorry, I'm not in a ****ing good mood today! ...

Sorry to hear about the trouble with a past client David, it is not fun and can happen for any reason at all.

[David A. Andersen]

Thanks, but I don't even think about this stuff as I start my day!! ....

He can pound sand, and I am prepared after every inspection to cover every thing I report on.

If I said it, you had better have proof because you can be assure that I in fact do!

[Jae Williams]

[quote=dandersen;682383]Thanks, but I don't even think about this stuff as I start my day!! ....

He can pound sand, and I am prepared after every inspection to cover every thing I report on.

If I said it, you had better have proof because you can be assure that I in fact do![/quote]

Man after my own heart.

If I said it, I'll write, sign it, and prove it!


(If I ever get to Tennessee I gotta look up David.)

[Sean Fogarty]

All i have is a 12 year old armstrong POS heat pump. I need zoned heating though. Second thought I will just use Wayne's sister she is nice and fat. Warm for the winter!