Return air vents...

I just added a 260sq ft room to my one store house. I now have approximately 2200 sq ft. I also have tons of windows in my house including 6 that overlook an outside atrium.
Even before I added the room the AC starts running around 10:30am and does not shut off until about 8:00pm. For the most part it keeps the temperature around 81 degrees in the middle of the day. Cannot get it to keep it any cooler.
I have one return air vent in a central hallway that connects all the rooms. The room I just added is warmer than the rest.
I currently have a 3.5 ton unit. I was thinking about moving to a 5 ton unit but a friend told me without another return air vent I will not see much more cooling that I already have. I am looking to get the temperature down to about 78 degrees.
Any advice on how to proceed would be much appreciated.
Thanks in advance,
James
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I have a 2600 Sq Ft home and only a 3 ton AC unit. I also have lots of large windows but can damn near freeze a glass of water on the coffee table. This tells me you must have something wrong with your AC unit. I would have your AC checked out as it may be low on freon. It shouldn't have to work that hard to produce cool temperatures. To make my AC more efficient I close all the downstairs registers to blow cold air to the upper levels only and closed doors to the basement since cool air decends. That was one thing that made things efficient. Hope that was of some help....Jim

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I have had AC checked out everything fine from 2 different contractors. They say just two many windows for this Houston climate.
"Jim" <jim.morris> wrote in message

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If there's nobody home on work days, can you close all the window coverings (curtains, blinds, etc)? That can make a world of difference.

ton
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You might be better off getting a second unit and having each unit handle different areas of the house; save you the expense of trashing your current 3.5 ton system. I'd consult someone well qualified in both Manual J and Manual D (check the ASHRAE website www.ashrae.org) and in system design. It'll cost you less in the long run and you'll be more comfortable.
Now I'm almost convinced that my installer put in too large of a unit: 5 tons for 2400 sq ft house also in Houston, few windows. I knew I should have insisted on the Manual J load calculations. See the current issue of Fine Homebuilding magazine for an eye-opening article on AC installations. For your reference, I have no problem cooling down to low 70's (any colder and I need a jacket).
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"Jim" <jim.morris> wrote in message

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Your A/C sounds like it is sized properly. I have 2700 sq feet and two A/C units that total 4 tons. Check for leaks in the duct work. Are all your registers open? A technician should check your unit for the correct amount of charge, well worth the $100 service call.

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Follow the advice of others here and have a contractor run the Manual J on your home.

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If you didn't install additional ductwork in the addition then it isn't receiving any airflow.

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It's more than just the return vent. The larger unit moves more air, not just on the intake side. There are more possibilities than we could go over here that can affect the operation so it would be better for you to contact a reputable company to offer suggestions.
- Robert

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What was the Manual "J" calculation for the existing home then what is the calculation of the new addition? Without those you are strictly guessing. One may be right but then may be wrong without the calculations.
Don't tell me what I can understand, tell me what I can't mis-understand (Gen. Douglas McArthur)! No matter what you do you are a problem solver....what do you do? Arthur, Website: www.arthurhewett.com Email: snipped-for-privacy@bellsouth.net

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You dont have it running but 9.5 hrs a day !!! That is minimal in your climate for a proper unit. Now if you set it at 72 and left it it would work and save you thousands in equipment , Oversize it and the humidity wont be pulled out and you will be clamy and as pissed as a Clam.
Do a load calc , do a blower door test and IR photo . Upping insulation to Modern not Minimum standards is going to save you juice to the juice co. Even window and door replacements are a smarter option. I still dont get it , you think you unit is undersized but run it only 1/3 of its design capacity. RUN IT , 24 hrs for a few days , you will be happy.
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Thanks for all the responses. I have had two companies out and they both say that my AC is working fine.
I will check this Manual J out to do some calculations. I think the large number of windows and especially the atrium (which is like having a 120 degree room in the middle of my house) is what is killing me. I would be happy if I could get it down to 76 degrees on a 93 high humidity day down here in Houston.
I guess what I have heard is that putting in another return vent won't necessarily fix my problem.
Thanks,
James

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Why not another supply to the Atrium, At night you dont cool with the AC off, as the load is in the house, that is your only time for recovery and to see how it balances out. Set it at 70 for 3 days and see if it doesnt do the trick. Many people are undersized or have poor equipment and dont cool running 24x7, they are the ones with big problems, not you.
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I forgot to mention I am oversized and purchased a dehumidifier to add heat load and dehumidification. Add a few more tons you may clamy as I have been. and need a dehumidifier. Run it.
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Call your utility company & ask if they still have the service of a Manual "J" as well as check your home for conservation. I have been in South Florida for awhile and we to have a hot humid climate to deal with.
Don't tell me what I can understand, tell me what I can't mis-understand (Gen. Douglas McArthur)! No matter what you do you are a problem solver....what do you do? Arthur, Website: www.arthurhewett.com Email: snipped-for-privacy@bellsouth.net

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Some thoughts.
1. Replace all your windows with low-e double pane glass. And solar screens.
2. Add insulation in your attic.
3. Go ahead and add another return, but put it high on the wall, so it draws in the hotter air. And if you have pleaded filters, you may want to try fiberglass spun filters that permit greater air flow.
4. Try leaving it on 76 for a week without setback and you should be more comfortable. And it should run solid from about 10 am to 9pm during July and August.
5. Should you decide to upgrade, spend a little(lot) more and get a multispeed condensor. American Standard make a nice one.

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