Expert Package (all-in-one) advice needed

13 years ago

I live in Ft. Lauderdale (Southeast Florida) and will be replacing my existing 3.5 ton Kenmore packaged unit. When I purchased this house (CBS construction) 15 years ago, it had originally a 3 ton Armstrong package unit and the house had 1,483 SF under air. Since then I replaced the 3 ton Armstrong package unit with a 3.5 ton Kenmore (13 yrs ago), tested and repaired the duct system (13 yrs ago) and had insulation (R30) blown in the attic (12 yrs ago). The house had a Florida room which I converted (6 yrs ago) that it is now under air. My living area under air is now 1968 SF. When I converted the Florida room (stucco), I added two (2) supply drops (6") flex with 10x6 vents and one (1) 8" flex with 12x6 vent for the cooling of the flat roof Florida room. The Florida room (insulated) which has many windows faces West and gets the majority of the heat in the afternoon.

Because I live 1 mile from the beach, my coils have deteriorated and the unit is working much harder. I am looking to replace the Kenmore (12 SEER) 3.5 ton unit with a 14 SEER variable blower unit from Bryant or American Standard. The model on the Bryant (Premium) is 707CNX (http://www.bryant.com/products/packaged/ac/preferred.shtml) and the American Standard (Allegiance) is model 4TCY4 (http://www.americanstandardair.com/HomeOwner/FullSystems/AllInOne/AirConditioner/Allegiance4TCY4.aspx). Both units have a 10 warranty on compressor, coil and parts. The Bryant unit is louder (77db) versus the American Standard (72 db) for the 4 ton unit. The American Standard has the Spine Fin which sounds a little better, but Bryant has a nice 100% money back guarantee if I don't like the system.

I understand that over sizing isn't good and is less efficient in regards to usage of electricity. Most AC dealers told me to go with a 4 ton unit but also couldn't assure me that my ducts wouldn't sweat. What would you experts do? My return grill in the house is 18x24 (in the hallway), then it goes to 12x24 space under a closet for 15 feet to the air conditioner. Some said that the return grill or the amount of air flow is sufficient and some said to just make a larger return grill (24x24). I don't understand how a larger return grill will do anything if the return under the closet goes to 12x24. Then there is a question about the size of the duct work. Again all said that it wouldn't be a problem, especially with the variable blower but really didn't give me enough confidence to proceed with a 4 ton unit. Two years ago I had another duct test completed by our local utility company and they said there were no leaks. Just for further information, the house was designed for a top/bottom packaged air and the existing Kenmore is a side by side. I don't think there are many good top/bottom packaged units on the market and with the shroud most use the side by side setup. My current airflow to the rooms (vents) isn't that strong and I think that another 200 CFM (3.5 to 4 ton) could be tolerated.

So, I guess my questions would be: Should I stay with a 3.5 ton unit and which package unit do you like better? I need to stick with at least a 14 SEER unit and the best 15 SEER units surprisingly do not qualify for the tax credit. Please also comment on the return grill issue and your thoughts about the duct concerns. I know that most manufactures don't give much information on the packaged units online, but I have the detailed specs for both units which I can pass to you. Many thanks for all your help in advance.

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Comment (1)

zippyhvac
13 years ago
last modified: 9 years ago
How are you filtering your return air? A larger grille will help with air noise, and could help airflow if it's a filter-grille (less restriction) - but otherwise, especially if the ductwork is "necked-down" it really can't help with return capacity.

Insufficient return capacity could cause sweating - because the return gets "too cold" from the coil - because there isn't enough volume of air passing over it.

A temp drop of over 20 degrees at the coil is bad because it shows that there isn't enough air making it over/through the coil - and sweating occurs because that super cold air could be 50 or more degrees cooler than the air in your attic.

The big temperature differential, along with the very high humidity you have there gives you very tough conditions to prevent condensation & sweating. Your ductwork needs to be insulated extremely well, and your return air setup must be setup perfectly to prevent problems.

Whatever contractor you choose, be sure to send them packing if they aren't doing things like measuring temps and airflow into each room, and providing you with room-by room analysis of system requirements.
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Expert Package (all-in-one) advice needed

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zippyhvac

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