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Old 08-04-2008, 11:02 PM
 
Location: Las Vegas, NV
107 posts, read 368,700 times
Reputation: 45

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We just closed on a new (construction) house last week in RBR. It is 2700 Sq feet-two story. Three bedrooms and a large family room are upstairs.

The house only has one A/C unit and I am concerned. I have been reading through posts on here (especially the CPS posts) and a lot of people have 2 units. I have asked our builder several times about having two units, but he has stated that the one we have (sorry, I don't know the size) is adequate for the house.

Is there a "typical" standard in the Texas heat to have two units for two stories? Our house does have a radiant barrier.

We have only had the house for 6 days. The thermostat (downstairs) is set on 78. We have two indoor thermometers. The downstairs one says 76, and the upstairs won't go below 83 at any point of the day. The house was just balanced...but it seems like it is off balanced again. I am concerned that it does need 2 A/C units.

Does anyone have a house around 2700 Sq feet--2 story--with only 1 A/C unit. The builder told us that if we got two units, our CPS bill would be much higher.

Thanks in Advanced!
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Old 08-04-2008, 11:21 PM
 
90 posts, read 313,579 times
Reputation: 27
Id like to hear what others say as our house is being built and will only have one ac unit too for 3000 sq ft.
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Old 08-04-2008, 11:26 PM
 
Location: San Antonio
2,216 posts, read 3,982,829 times
Reputation: 1179
We have one unit, 2 story house. The unit is Trane and it is huge. I will tell you every other two story we have had has had two units and our bills were very high while the upstairs remained HOT. Due to the size of this unit the house is cool and the bills aren't outrageous. Sq ft 2300 roughly. We keep it at 78.
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Old 08-05-2008, 03:10 AM
 
Location: Wiesbaden, Germany
13,807 posts, read 26,289,640 times
Reputation: 3987
3000 sq. ft. is somewhere around where they go from one large unit to two smaller units. My house is 2700 sq. ft. also and only has one unit. It works, but I'd personally rather have two smaller ones. Hopefully you didn't get a Goodman like I did because I've had the parts replaced quite a few times, especially the inside coil. Definitely might want to consider an extended warranty. I (luckily) got one and I'm usually very against them, but this one was worth at least $5K in repairs so far.
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Old 08-05-2008, 03:48 AM
 
Location: SoCal-So Proud!
4,263 posts, read 9,690,898 times
Reputation: 1541
Quote:
Originally Posted by Julie1226 View Post
We just closed on a new (construction) house last week in RBR. It is 2700 Sq feet-two story. Three bedrooms and a large family room are upstairs.

The house only has one A/C unit and I am concerned. I have been reading through posts on here (especially the CPS posts) and a lot of people have 2 units. I have asked our builder several times about having two units, but he has stated that the one we have (sorry, I don't know the size) is adequate for the house.

Is there a "typical" standard in the Texas heat to have two units for two stories? Our house does have a radiant barrier.

We have only had the house for 6 days. The thermostat (downstairs) is set on 78. We have two indoor thermometers. The downstairs one says 76, and the upstairs won't go below 83 at any point of the day. The house was just balanced...but it seems like it is off balanced again. I am concerned that it does need 2 A/C units.

Does anyone have a house around 2700 Sq feet--2 story--with only 1 A/C unit. The builder told us that if we got two units, our CPS bill would be much higher.

Thanks in Advanced!

Is there a room over the garage? 4 sides brick? Brick is king in Texas.
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Old 08-05-2008, 06:08 AM
 
Location: Charleston, SC
5,615 posts, read 12,789,652 times
Reputation: 2534
I'd call the builder out on this one quick before any warranty periods start to slip.
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Old 08-05-2008, 06:56 AM
 
Location: San Antonio
4,149 posts, read 9,303,154 times
Reputation: 3308
It's probably not a matter of needing 2 units. More units doesn't necessarily mean colder. You may have a problem with the zoning of the unit.

As someone said above, 3000 sf is where two units traditionally start being used. Anything less can result in much higher bills, but the same results
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Old 08-05-2008, 07:11 AM
 
1,740 posts, read 5,184,554 times
Reputation: 336
A few factors to keep in mind:

Do you have radiant barrier?
Low-e windows?
Do you have living space above the garage?
How many return air ducts do you have?
Where are they - in the wall below a unit or in the ceiling - especially upstairs since hot air rises?
Is your unit in the attic or in a closet on the second floor?
What brand unit do you have?
Do you have a variable speed fan?
Who was your builder?

I have a 3,215 square foot home with 2,775 square feet downstairs and 440 upstairs. The house has one five ton unit with three zones (two down and one up) and three return air ducts located in the ceiling. My A/C unit is in the attic with all return air ducts located in the ceiling (two down and one in the guest suite upstairs). We have radiant barrier and doubl paned low-e windows all around with shutters and/or curtains on all windows. Our A/C system cools the house just fin - even the upstairs. In addition, since 2,775 square feet has a hot attic above the living space we have more hot exterior surfaces than you do since your attic only covers 50-60% of total living space.

I would guess that while your unit may be sized right - that you do not have proper return air ducting upstairs. For a unit to cool comfortably your return air ducts need to be in the ceiling. If your return air duct is not in the ceiling on the second floor it is hopeless to get that hot air from the upper areas in the rooms upstairs. If you do have return air ducts in the ceiling of the second floor - then I suspect they did not run large enough ducts to your second floor bedrooms.

One zoned unit should be able to cool a 2,700 square foot house just fine if it is ducted and sized correctly.

Last edited by banker; 08-05-2008 at 07:19 AM..
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Old 08-05-2008, 08:33 AM
 
Location: Mid South Central TX
3,183 posts, read 7,413,016 times
Reputation: 2188
Yes, ducts are key here. In our old house (2500 sq ft, 2 story) we had one unit. Because we had the western exposure in the back (where all of the windows are), I insisted on extra ducts, and I was glad that I did. Unfortunately, it was not zoned, and so our upstairs was always HOT.

IIRC, all new construction in Texas is required to have low-e windows. Solar screens help, too. At one time, I believe the standard was one ton (capacity) per 500 sq ft. That would make sense with the 3000 sq ft/2 units, as I think, most residential units are 5 ton and below...
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Old 08-05-2008, 08:47 AM
 
1,740 posts, read 5,184,554 times
Reputation: 336
Quote:
Originally Posted by pobre View Post
Yes, ducts are key here. In our old house (2500 sq ft, 2 story) we had one unit. Because we had the western exposure in the back (where all of the windows are), I insisted on extra ducts, and I was glad that I did. Unfortunately, it was not zoned, and so our upstairs was always HOT.

IIRC, all new construction in Texas is required to have low-e windows. Solar screens help, too. At one time, I believe the standard was one ton (capacity) per 500 sq ft. That would make sense with the 3000 sq ft/2 units, as I think, most residential units are 5 ton and below...
Yes - we picked our lot for exposure relative to the number of windows. The western side only has three windows out of the 18 large windows in our house. As for the tonnage per square feet - 500 square feet per ton is a good starting point. But - the exposure, lack of radiant barrier and cubic feet of space can cause that number to go up or down. For example - I have a friend that has a seven year old Pulte house in Schertz that lacks a radiant barrier and double paned windows and has a two story entry and living room. He has a 2,700 square foot house with one unit and the system runs nearly 24/7 - never really cooling the second floor. He had a load test done on his house and determined that he needed two units with about 6.5 tons based on the cubic feet, exposure, poor windows and lack of radiant barrier. Had he had a radiant barrier and double paned windows along with better ducting - the heat load test indicated he could have had one five ton unit easily.

Our floor plan has no two story ceilings - our highest ceiling is 10.5 feet. I really wanted to limit the cubic feet of space that I had to cool and heat. I guess I would ask if the OP has any two story spaces as that effectively adds to the square footage picture originally outlined.
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