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Old 06-17-2008, 07:47 PM   #1
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How long should it take to cool one degree


Hi, new here,

I have purchased a 3 ton carrier central air unit (outside and inside) on a 10 year old 1350 sq ft house with added insulation in the attic, they did not change the furnace or the blower. They came out and gave me a quate and I told them I want the air to come down when I turn it down. (from 75 to 73) It is now reaching 95 - 97 degrees here in Houston, Texas and the unit takes at least one hour twenty minuites to cool one degree (from 75 to 74) and they are tring to tell me this is normal. Am I expecting too much, or are they trying to weezel out of this.

Thanks in advance for your support and comments.


Last edited by ctd461; 06-17-2008 at 07:50 PM.
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Old 06-17-2008, 08:23 PM   #2
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How long should it take to cool one degree


I have a 3ton AC in a 1200 sq.ft house, last week we had similar weather and I can drop from 80 to 73 in less than an hour.

Sounds like somethings not right.

How long should it take? Well it depends, theres no quick answer, but for a 10 year old home and furnace a degree drop in an hour and a half is not normal.


Last edited by 8 Ball; 06-17-2008 at 08:31 PM.
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Old 06-18-2008, 05:05 AM   #3
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How long should it take to cool one degree


I agree with 8 Ball, something is not right.

Your furnace is not old enough to be a problem except that the blower speed may need to be switched to a faster speed. I don't live as far south as you and not sure how they size furnaces in your area, so question blower speed.

Also on a 10 year old home I would assume it has reasonably good insulation.

The only other question that occurs to me is being as far south as you are, is the AC unit properly sized?
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Old 06-18-2008, 11:50 AM   #4
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How long should it take to cool one degree


I have a similar sized house of about that age and did an A/C replacement last year. They put in a 4 ton unit w/ a SEER of 13, so from what I read/learned, your unit seems kinda undersized. Although I live in Las Vegas and don't have the humidity that you do, so I don't know if that's a factor. I would guesstimate that when the air kicks in, w/ the temp 95-100, it 'normally' takes about 15 minutes to kick back off, dropping the temp inside by a degree or two. Of course, when we hit 110, things run almost all the time. Lots of variables there, but still, what you're experiencing doesn't seem right. Is your power bill thru the roof? (as compared to what it was before the unit was installed?)
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Old 06-18-2008, 07:12 PM   #5
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How long should it take to cool one degree


the energy usage per kilowat hour is the same, I was hoping for less, but I'll be happy with the same as long as the system dose what i say do when i say do it. It sounds like the concenses is it should cool one degree in 10 to 15 minuites. I believe I need more air flow. the tech comes tomorrow, but I already gave him a peace of my mind. We'll see what he dose. If they don't take care of it, the only thing I know to do is report them to the BBB. any other ideas?
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Old 06-18-2008, 07:53 PM   #6
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How long should it take to cool one degree


Do you have cold air blowing out of your vents? A typical air conditioner will supply 17 - 24 degrees F below the air temperature of the air being drawn into the furnace (return air). At 80 F return you can expect approx 60 degree supply temps. If the air is nice and cold, then you have to start looking at your ducting and/ or the position of your thermostat..airflow should be fairly strong and the thermostat should be in a location where it can read a good sample temperature. Do you leave your ac on or just turn it on when the house is already hot? It can take several hours to cool down all the items in your house especially if it is quite warm. Try leaving your ac on and seeing if it ever does reach it's setpoint. Just make sure your filters are clean and that you do NOT see any signs of ice on any of the refirgeration piping. Hope this helps.
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Old 06-19-2008, 01:11 AM   #7
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How long should it take to cool one degree


Good point on the air temp. I have a laser thermometer & my readings run around 60-62 degrees (after the unit has run for a few minutes to clear out the hot air).

You might try appealing to the manufacturer?
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Old 06-19-2008, 07:33 PM   #8
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How long should it take to cool one degree


just an update, turned out the tech was not so bad, He is going to double my return air and add another duct and vent on the west side of the house. the return duct is 24" with a 15' run. he said that was too long of a run for the return air. I'll let you know how it turns out. thanks for yalls input.
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Old 07-07-2011, 11:07 AM   #9
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How long should it take to cool one degree


It is not just the air temp that affects the comfort level. You also have to consider that all the objects in your house (the walls, ceiling, floors, furnature, everything) are at room temperature and will continue to radiate heat into the room till they too have been cooled. If I understand correctly radiant heat will continue to warm you even though the air around you is cool. Humidity too has to be removed from all objects that will hold it such as beds, fabric upholstery, etc. and this takes days, not hours. Run your AC at night when the temp outside is lower and you will benefit during the day.
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Old 07-07-2011, 12:13 PM   #10
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How long should it take to cool one degree


It really depends on a number of factors in how long the unit will run to cool the house. That is, the set point of the thermostat, how many times are people running in and out of the house, indoor humidity level, outdoor temp & humidity, which the structure will be affected, especially if no trees to shade the structure, temp of the attic air space.

If I set my thermostat at 72, when it is 90 plus outside, with a humidity of 60's to 70's, my system will run for almost three hours to keep up to keep the house cool, due to one factor, is no insulation in my walls, but attic is well insulated. Keep in mind, there is a number of factors, as listed above, including how well sealed the doors are, the windows, exhaust fans for bathrooms have dampers to seal from conditioned air escaping through chimney effect, same with dryer vent.

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