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Old 01-17-2013, 08:19 AM   #1
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AC vs Heat difference in travel?


All,

I have been running into a bit of heating issues to which a couple of the contractors that I have brought out stated that I the equipment was fun and that I needed to rerun my vents in the attic.

My split on my AC is about 2-4 degrees in the different rooms minus the airflow. My split on my Heat is much larger in difference being about 30 degrees.

I am not an HVAC expert but, does Hot vs Cold air travel that different down my longer runs that it could cause a 30 degree differential?

Thanks,
randy

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Old 01-17-2013, 09:32 AM   #2
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AC vs Heat difference in travel?


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All,

I have been running into a bit of heating issues to which a couple of the contractors that I have brought out stated that I the equipment was fun and that I needed to rerun my vents in the attic.

My split on my AC is about 2-4 degrees in the different rooms minus the airflow. My split on my Heat is much larger in difference being about 30 degrees.

I am not an HVAC expert but, does Hot vs Cold air travel that different down my longer runs that it could cause a 30 degree differential?

Thanks,
randy
Not totally sure I get what you're saying, but if you're saying the temp difference from your return grill to a supply vent in A/C is only 2-4 degrees that isn't normal. And while cold air is heavier and requires more force to push it shouldn't make that big of a difference.

Do you by chance have an electric furnace?

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Old 01-17-2013, 10:40 AM   #3
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AC vs Heat difference in travel?


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Not totally sure I get what you're saying, but if you're saying the temp difference from your return grill to a supply vent in A/C is only 2-4 degrees that isn't normal. And while cold air is heavier and requires more force to push it shouldn't make that big of a difference.

Do you by chance have an electric furnace?
I apologize. Between all of my vents in my house while running the AC the average differential at the grill is about 2-4 degrees. When I switch to the heat the average differential at the grill for two of my long runs is about 30 degrees.

I do have an electric furnace.
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Old 01-17-2013, 12:14 PM   #4
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AC vs Heat difference in travel?


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I apologize. Between all of my vents in my house while running the AC the average differential at the grill is about 2-4 degrees. When I switch to the heat the average differential at the grill for two of my long runs is about 30 degrees.

I do have an electric furnace.
OK still not sure I'm getting what you mean, but if your saying that you only have 2-4 degrees difference from the air entering your a/c to the air leaving your a/c something isn't right & I highly doubt it has anything to do with ductwork. Electric furnaces can have elements stick on. One element stuck on will basically negate all your cooling & leave you with air leaving your a/c at about the same temp it enters. But for heating it will heat normally. Kinda sounds like your issue.
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Old 01-17-2013, 12:29 PM   #5
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AC vs Heat difference in travel?


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OK still not sure I'm getting what you mean, but if your saying that you only have 2-4 degrees difference from the air entering your a/c to the air leaving your a/c something isn't right & I highly doubt it has anything to do with ductwork. Electric furnaces can have elements stick on. One element stuck on will basically negate all your cooling & leave you with air leaving your a/c at about the same temp it enters. But for heating it will heat normally. Kinda sounds like your issue.
Let me try representing my data differently:
When I turn on the AC the following temps are what I receive from my vents: (each item below represents a vent in a different room)
  1. 57
  2. 54
  3. 55
  4. 52
Degree differential: 2 degrees

When I turn on my Heat the following temps are what I receive from my vents: (each item below represents a vent in a different room)
  1. 120 degrees
  2. 122 degrees
  3. 90 degrees
  4. 91 degrees
Degree differential: 30 degrees


Is there a reason that my AC differential would be approx 2 to 3 degrees but, with the heat it is approx 30 degrees?
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Old 01-17-2013, 12:44 PM   #6
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AC vs Heat difference in travel?


Measure the temperature at your main return grill. The farthest away from that grill should be the coolest in heating season, and the warmest in cooling season. The temperature you posted is a bit unusual but by no means impossible. Where the ducts run and the distance is very important. It's possible the ducts run through cold areas which will drop the temperature in the ducts. It's also possible that the ducts with the warmest temperature also have the least restricted flow of return air. Are the doors closed when you take these measurements? If the return air is impeded, the velocity at any given duct will be lower. When they say re-run.....how are they run now? Also the fan speed may be different in heating than cooling. If you have any duct leaks this could be an indication of that.
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Old 01-18-2013, 07:36 AM   #7
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Measure the temperature at your main return grill. The farthest away from that grill should be the coolest in heating season, and the warmest in cooling season. The temperature you posted is a bit unusual but by no means impossible. Where the ducts run and the distance is very important. It's possible the ducts run through cold areas which will drop the temperature in the ducts. It's also possible that the ducts with the warmest temperature also have the least restricted flow of return air. Are the doors closed when you take these measurements? If the return air is impeded, the velocity at any given duct will be lower. When they say re-run.....how are they run now? Also the fan speed may be different in heating than cooling. If you have any duct leaks this could be an indication of that.
The temps posted were taken within about 2 hours of each other and the air at the return was approx 72 degrees.
The lower temps on the heat side are on the two longer runs (50ft+).
The airflow between all of the output from the ducts are really good.

Given the possible idea of a leak in the duct wouldn't i be seeing a larger differential on my cooling side as well?
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Old 01-18-2013, 09:05 AM   #8
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AC vs Heat difference in travel?


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The temps posted were taken within about 2 hours of each other and the air at the return was approx 72 degrees.
The lower temps on the heat side are on the two longer runs (50ft+).
The airflow between all of the output from the ducts are really good.

Given the possible idea of a leak in the duct wouldn't i be seeing a larger differential on my cooling side as well?
I would think so. It could be your duct isn't insulated and where it runs through the attic if it's hot in there at the time you're testing it it would cause you to lose cool, but not heat because the attic's already hot.
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Old 01-18-2013, 11:59 AM   #9
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AC vs Heat difference in travel?


The larger the temperature difference between the air in the duct and the attic temp the faster it transfers heat. Fourty degree Ac air in a 50 degree attic will not pick up much heat but 130 degree heat will lose a lot to the attic if the ducts are not insulated well. You'll see exactly the opposite in the summer when the attic is 130.

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