Temp Splits

Archive Public Archive
#1

Originally Posted By: egriffin
This post was automatically imported from our archived forum.


Are the splits usually the difference between temps at the intake and the exhaust vents?


If so, I checked on yesterday that had a difference of 34 degrees. Is that really good or is there such a thing as too much of a drop?

#2

Originally Posted By: rsummers
This post was automatically imported from our archived forum.


That would be a extremely high split that could be caused by a number of things duct work not properly sized, blower motor going out ,plugged evaporator coil to name just a few. Depending on humidity the split should be between 12 and 20 degrees.

#3

Originally Posted By: Blaine Wiley
This post was automatically imported from our archived forum.


Most things I have read (and the correct answer on the tests) says the split between supply and return air across the coil should be between 14 and 22 degrees. Assuming your thermometer is accurate, sumpin am definately rong.

#4

Originally Posted By: jpeck
This post was automatically imported from our archived forum.


And should be checked as close to the coil as possible. Not just in a convenient supply register or return air grille.

–
Jerry Peck


South Florida

#5

Originally Posted By: cbottger
This post was automatically imported from our archived forum.


Would have to agree 34 degrees is an indication of problems, but would also recommend that your pocket thermometer if that is what you are checking temps with be calibrated in a glass of ice water to 32 degrees as they can get out of range every time they are dropped. I do not prefer to stick my neck out unless I am positive that I am right.

–
Don’t argue with an idiot someone watching may not be able to tell the difference.

#6

Originally Posted By: jpeck
This post was automatically imported from our archived forum.


they do not need to be “calibrated” to the ice water if checking TD, but “calibrated” to each other (because you are checking difference, not actual temperature).


Insert your thermometers, wait for them to stabilize, take the readings, swap thermometer positions, wait for them to stabilize again and read them again.

They should be reading within 1 degree of each other regardless of which thermometer is where.

To calibrate with glass filled with ice, fill a glass with ice, pack in as much ice as you can, add enough water to fill the the glass to the top of the ice, repack the ice and add more if you can. Insert both thermometers and adjust to 32-33 degrees. That is about as close as those thermometers will read anyway

--
Jerry Peck
South Florida

#7

Originally Posted By: dbowers
This post was automatically imported from our archived forum.


Two thoughts on measuring TD’s (temperature differential).


Measuring at the evaporator coil will absolutely give you the best readings and show what the unit is actually doing.

Unfortunately too many HI's and even technicians forget that we don't live at the evaporator coil. Taking the TD at the supply and return air registers (lets say in the livingroom) will tell you whats coming into the LIVING area of the house - AND folks thats where your buyers LIVE AT.

I take a TD at the registers to start with - if its good there, we're good to go. If its NOT good there, I will then take a reading at the evaporator coil later on when I'm by the furnace. If its good there - the UNIT is producing OK but we have a problem getting it delivered to the ROOMS.

At that point we want to recommend having a competent HVAC contractor address the issue. This is just a thought from someone with a lot of years doing HI's and a mechanical engineering degree (major in HVAC).

#8

Originally Posted By: Blaine Wiley
This post was automatically imported from our archived forum.


Dan,


Zackly the way I do it, too! Nice to know I'm not the only one!!! ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

#9

Originally Posted By: jpeck
This post was automatically imported from our archived forum.


dbowers wrote:
Two thoughts on measuring TD's (temperature differential).

Measuring at the evaporator coil will absolutely give you the best readings and show what the unit is actually doing.

Unfortunately too many HI's and even technicians forget that we don't live at the evaporator coil. Taking the TD at the supply and return air registers (lets say in the livingroom) will tell you whats coming into the LIVING area of the house - AND folks thats where your buyers LIVE AT.


I think those HIs and techs are aware of what you are leading to, but acknowledge that ...

... that has nothing to do with the TD. If the TD is taken at the unit (and I seldom take TDs anymore, but this is a previous long thread as to why), it is not telling you what you are trying to find out.

Taking a temperature measurement (not a TD) at the room will tell you what is going into the living space.

If there is a problem at the supply, it is not indicative of a problem with the unit, but of a problem at the unit OR in the duct work. Taking the TD at the unit and a temperature at the room gives an indication the unit AND the duct work.

--
Jerry Peck
South Florida
#10

Originally Posted By: Vince Santos
This post was automatically imported from our archived forum.


[quote=“dbowers”]


I take a TD at the registers to start with - if its good there, we're good to go. If its NOT good there, I will then take a reading at the evaporator coil later on when I'm by the furnace. If its good there - the UNIT is producing OK but we have a problem getting it delivered to the ROOMS.quote]

What should the air temp be coming out of the registers, lower level and second story?
Also, is this part of a typical inspection?

--
Desire is half of life, indifference is half of death.
--Kahlil Gibran