One HVAC system for my 2 story house


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Old 05-21-12, 11:52 AM
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One HVAC system for my 2 story house

I have a story and a half house in New Orleans built in 1960. It is 2100 sq ft with about 550 sq ft upstairs (two bedrooms with walk-in closets and a small full bath). One vent in each bedroom.
My current system is a upright 4 ton lennox gas furnace with an unknown 3.5 ton Acoil with expansion valve and a Janitrol single stage 3 ton 10 SEER condensing unit. I have hard internally insulated ducts. This system has been Ok but inadequate on really hot days here in New Orleans. The original 3 ton system was installed in the the house before the back den (510 sq ft) was added to the house so it is probably (ya think?!) undersized.
I am getting a Honeywell HZ322 zone controller with a single stage cool thermostat downstairs and a 2 stage cool thermostat upstairs so I can turn the fan on when the temperature upstairs is at the set temp then turn on the AC when it goes 1 or 2 degrees above set temp. The downstairs single stage thermostat works as normal. Yes this could lead to some downstairs overcooling which may require dampers. And yes some humidity may be sent back into the house from the coil during fan only operation but I find that more comfortable than letting the upstairs bedrooms (mine) get too hot while cool air is downstairs that can be circulated to upstairs for a while before the system needs more AC.
I would like to get a furnace with variable speed or at least multiple speeds (low heat, low or med/low fan only, and high AC).
What are the costs and benefits (savings, quiet, comfort,etc) of variable speed vs multi speed furnaces and the cost benefits of 14ish vs 16ish SEER and 1 vs 2 stage cooling? I was planning on getting a 4 ton system this time around.
Any suggestions on size, type (stages, variable spd etc), and brands/models?
Thanks
 
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Old 05-21-12, 07:24 PM
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first off, if you want your air flow modulated, you need a variable speed blower. multi speed isn't going to do anything for you because you have to manually wire those for the speed desired. second, if your looking to control upstairs and downstairs seperately i would go with a 2 zone system, they are quite pricey but if you can get to your ducts that would be the way to go. do you have any ducts running to your den?? if not don't upsize if your house was designed for the 3 tons of cooling. since your in a climate where ac is used much more often than not, i would go with a 2 stage condenser and get that higher efficiency. as far as brands, i like the one with the best warranty, goodman/amana are good enough for me.
 
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Old 05-22-12, 02:15 PM
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Going 2 zone

As I stated in my post, I am installing a Honeywell HZ322 zone controller not so much to separately cool my upstairs and downstairs but to install another stat upstairs that will turn on the fan and circulate cool air from downstairs up to the second floor as well as turn on the AC when it gets hotter.
I have researched some furnaces and some have multispeed, some have variable speed and some even have very slow fan only for circulating air through the house. The Goodman GME8 80% AFUE Two-Stage (Convertible), Multi-Speed Multi-Position Gas Furnace features.... a super-efficient EEM circulator motor that saves energy. Further in the specs it says Low constant fan allows homeowner to activate the low heat speed to efficiently circulate air throughout the home.
The Goodman GMV95 95% AFUE Two-Stage, Variable-Speed Gas Furnace features ... Ultra quiet variable speed circulator motor that gently ramps or down according to heating and cooling demands. Further in the specs it says Extra-low constant fan allows homeowner to activate very low speed to efficiently circulate air throughout the home. This setting costs as little asa 75-watt light bulb to operate. Then it says Quiet two-speed induced draft blower.
See how confusing it is?


Is this a multispeed or variable speed blower. What are the different kinds of blower motors? [SIZE=3] Isnt Variable speed always more expensive to buy?
My 500 sq ft den was added on to the house after the orginal 3 ton AC was installed. A duct was added to the system to feed the Den. I checked some online resources for calculating required heating and cooling and it said for a 2100 sq ft home in my zone I need 4.65 tons of cooling. I think with a few more energy savings improvements to my house a 4 ton will be perfect. My old 3 ton condensor with 3.5 ton evap on a 4 ton blower was OK most of the time, so a 4 ton should be just right.
[/SIZE] I am still debating two stage condensing units. They are more expensive too, right?

 
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Old 05-22-12, 05:33 PM
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yes variable speed motors are much more expensive and two stage condensers are as well. if i were you I would install a ductless mini-spit for the den and remove the ducts feeding that area. replace your 3 ton condenser with a 3.5 and go up to a 4 ton A coil
 
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Old 05-22-12, 05:37 PM
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as far as the 2 zone system goes w are on two different wave lengths. i'm talking about a two zone duct system. motorized dampers with a static pressure sensor and a bypass. look it up and read some on it. this would be the way to go, especially since you wouldn't want to over cool any area of your house.
 
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Old 05-22-12, 07:37 PM
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Ok first you have hot and cold spots now so we know the duct is not sized correctly. So to fix this the duct is going to have to be fixed. A multi speed blower will only fix small temp difference. Next you need a heat load done on the house. This is the only way to know what size unit you need. If your contractor does not do this find another one. This is the first most important step. If they skip this what else are they skipping. 3rd zoned systems are very troubled I'd stick with a un zoned system and safe your money on all the controls.
 
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Old 05-24-12, 08:54 AM
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Airman,
Why do you say my ducts are not sized right? They are hard internally insulated ducts with more volume than any flex duct i could fit between floors. When my AC is running it cools the house pretty well in all areas, except on really hot days here in New Orleans. New ducts would cost thousands of dollars and tear my two story house up. My system is 24 years old. I am pleased it has lasted this long but its time to change it out the main components and upsizing the condensing unit and evaporator to 4 tons should handle the really hot days better. I have had AC contractors say i need 5 tons which I know would be way too big. I have done online calculators which said 4.65 tons of AC needed.

I think you misunderstand my problem. My problem is when the AC turns off for some time and the heat migrates to the second floor and the cool air migrates to the first floor. At night the AC is off for longer periods thereby making the temperature difference between the first and second floor even greater making it hard to sleep. Adding a dual stage thermostat upstairs with a honeywell HZ322 zone control allows the fan to turn on when the upstairs gets to the set temperature which will draw cool air from downstairs (where the returns are) to the upstairs. Doesnt make any difference to the downstairs which is 3 times the size of the upstairs. If the upstairs continues to hotter and gets to the second set temp then it turns on the AC unit. If the downstairs gets to its set temp it will turn on the AC as well. I may add dampers if I find I am overcooling the downstairs too much at night. During the day and early evening the downstairs is the primary living area so the upstairs can be set a degree or two higher via programming.

RDSTREAM,
I have decided on a variable speed blower for both the comfort and the quiet. Since my 3 ton condensor did very well with my 3.5 ton A coil on my 4 ton furnace, I will look into the 3.5 ton condensor and get a 4 ton Acoil on the 4 ton variable speed furnace.
The den is usually the most comfortable room in the house. A mini split system would again cost several thousand bucks. I have a 1.5 ton wall AC in the den wal that is used when I have a party but very rarely otherwise.
I was looking at consumerreports.org and they showed that from 40,000 surveyed that goodman had alot more repairs (18) than American standard (11) and Trane and Rheem(12). I like Goodman's warrantees but dont want to be hasseled with repairs and outages. What is your repair experience.
 
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Old 05-25-12, 04:15 PM
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haven't been in the HVAC industry long enough to experience which units are giving me the most problems. American Standard and Trane are the same unit, like honda and acura. the trane just has more bells and whistles. Goodman brand is made by Amana so you can get a better quality unit with the Amana and the same great warranty.
 
 

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