# Average duct temp



## MikeT (Jan 23, 2006)

What should the average temp be at the ducts on a hot day???

I always assumed it should be in the 40's...
Am I off base ??????????


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## rjordan392 (Feb 9, 2005)

MikeT,
Yes, you are. I believe the temperature that installers look for is an 18 degree differance between incoming and outgoing air in a central air system. But air will gain a little heat as it travels through any length of duct. 
On my newly installed system, the 18 degree differance is what I have at the incoming side and plenum.


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## snapperhead (Jul 3, 2006)

the actual temp.on the coil between the fins will be close to that but the air in/out are the benchmarks.the colder the return is the colder the discharge will get ...so you would have to chill the house out so the rooms and its returns are 58F,then you will see a 40F discharge of air.always subtract from the return air reading that 18F and if your discharge is within 1F to 2F could also be more then 18 on a real dry day.another note AC in application of cooling must remove the moisture/Humidity first, then it can start to cool the air.you might feel it is cooling but that is that condensate line draining off your feeling to get to that 18F.that discharge duct needs to be tight on all connections and joints so the air out is true to the space with any leaking,and that is your tonnage going out where it shouldn't


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## Double-A (Jul 3, 2006)

snapperhead said:


> that discharge duct needs to be tight on all connections and joints so the air out is true to the space with any leaking,and that is your tonnage going out where it shouldn't


I'm sure I have leakage. I'm on crawl/partly finished basement with sheet metal ducts installed in 1966. I hope it cools off soon, so I can get under there and take care of that.:whistling


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## MikeT (Jan 23, 2006)

Well let me say 
Ambient about 88 humidity high 80% +++
Supply temp 63
Return 74
house temp 74-76
Set point 71 and running all day to never get there 
8 month old unit 2 ton Heat pump less than 1300 sq
one level ranch... one 20x20 return grid with 12 return duct


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## snapperhead (Jul 3, 2006)

shut the disconnect on the condenser and with a hose wash the coil up and down 360 around.if you have access to the compressor cover it with a garbage bag first just in case and wash from inside out if possible.restart the unit and check the insulated line either going into the condenser or coming out of the evap air handler...should be ice cold after about a 15 run if anything else you might be short on freon.if it had worked good last season and now its minimal you might of lost some during the winter.


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## snapperhead (Jul 3, 2006)

Double A....what you could do is shut the system off and if your duct is raw tin on the supply,HD has a red gallon of rubberized sealent that you could brush liberally around all the joints and take offs let it set overnight.the biggest leakage is under the air handler if it is laying on the attic joists,where the supply duct is connected and is the coldest spot off the cooling coil.a simple fix is just slide a 2X4 or 2X6 under the connection to the unit(cut to duct width)or take a roll of bailing wire and run it around and pull it tight.if you have flex coming off the supply trunk redo the tape if their and into the registers...try to make the duct takeoffs as straight as possible air move better on a straight line,if you have spider ARMS coming off the supply ruck cut them back as best as allowed by the attic...if you have a stand-up basement unit still do the sealant ans make sure the filter access is covered...the unit suck air wherever it can need that thrue temp from the house return.


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## MikeT (Jan 23, 2006)

snapperhead said:


> shut the disconnect on the condenser and with a hose wash the coil up and down 360 around.if you have access to the compressor cover it with a garbage bag first just in case and wash from inside out if possible.restart the unit and check the insulated line either going into the condenser or coming out of the evap air handler...should be ice cold after about a 15 run if anything else you might be short on freon.if it had worked good last season and now its minimal you might of lost some during the winter.


My unit was installed in January 06...Today it was 90 and humid and my duct temp was 70 and my return temp was 79 .. house temp was at about 77-80 ..

I need help


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## ATS (Jun 28, 2005)

It's difficult to properly charge a unit in Janurary on the East Coast. Call the installer back and ask him to verify proper charge by checking superheat and sub-cooling. Also, don't forget that 20 degrees below ambient is normal on the discharge. If your house is 70 and ambient is 90, you're doing ok.


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## ATS (Jun 28, 2005)

I thought I posted this already but a 2 ton unit may not be large enough for the heat gain of the house and this is all the little unit can do. Windows and insulation make a huge difference. This is why load calculations are done. :blink: I know I posted this already, am I losing it? Some single wide mobile homes require a 3 ton unit when you figure the heat gain and all that.


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