One AC Unit Zoned or Two AC units for 2 Storey House (Houston: live in, cost)

[gskataria1]

We are building a house in Houston and wanted to get an opinion on the Air conditioning. The house is 2800 Square feet. Is it better to get one 5 ton AC Unit Zoned (upstairs and downstairs) with 2 thermostats or two smaller AC units for upstairs and downstairs. I am not worried about the initial cost. What would be more efficient? I would be mostly using downstairs area (80% of the time) and upstairs (20%) of the time.

Thanks

[HookTheBrotherUp]

Well, having two units means that if one failed, you still have AC. Having no AC at all during the summer months is pretty bad.

That said, I have a two story house and I have only one unit, and electronically zoned. I've had it for about 18 months. It works great, saves cost because rather than having two units run at once, we just have one that cools the whole house. 5 Ton like your are thinking about.

Given that I would use my AC more hours than I would be without AC, it makes economic sense to go with one unit than operate two. My 2 cents.

[tampac66]

Originally Posted by gskataria1

We are building a house in Houston and wanted to get an opinion on the Air conditioning. The house is 2800 Square feet. Is it better to get one 5 ton AC Unit Zoned (upstairs and downstairs) with 2 thermostats or two smaller AC units for upstairs and downstairs. I am not worried about the initial cost. What would be more efficient? I would be mostly using downstairs area (80% of the time) and upstairs (20%) of the time.

Thanks

Do you know what kind of dampening system the single unit system comes with?

[DSL_PWR]

I think the zoned single unit system will be more cost efficient. If properly zoned and controlled it can cool/heat a home very well.

I would consider a Trane (5 ton zoned system) or a Carrier system.

[Hangster]

We had a single unit zoned in our first house (2 story). For our second home (one story), we had a 2 unit system. I preferred the 2 unit system so for our current house (2 story), we actually have a 3 unit system and couldn't be happier. I can't comment on the efficiency, as each house is different.

[Bentley2013]

For that size of a house, a 5 ton AC unit is plenty.

[PedroMartinez]

Originally Posted by HookTheBrotherUp

Well, having two units means that if one failed, you still have AC. Having no AC at all during the summer months is pretty bad.

This is how I feel. I've had a couple of ac problems at my house, and having that second unit running while waiting for the other to be repaired is quite awesome.

[usc619]

I would never use a single unit zoned for a two story. a single unit may be a little more cost efficient for you, but the bottom line is it saves the builder money.

[marksmu]

I had a single 5 ton on 3000 square feet. I hated it. If only one of the two thermostats called for AC, then it was too much air in the zone calling...What happened with mine is the upstairs was constantly calling for AC, it would turn on, cool the upstairs quickly, and shut off...cool air sinks, so the downstairs (with the exception of the west facing Master bedroom) stayed a little cooler than the upstairs in the mornings b/c cool air sinks...However, when the downstairs called for air, it was almost always sharing it with the upstairs - so the inevitable happened...it was hot downstairs in the late afternoons b/c the direct sun was unbearable. My master bedroom was 10 degrees hotter, even after they "balanced" the unit for the tenth or twelfth time.

Also, I found that because the upstairs cooled too fast, the humidity was not properly removed from the house all the time...The humidity levels hovered around 78-81% which is too high....I now have several smaller zoned units in a different house that are sized properly without dampers...the humidity is in the 35-41% range, and I pay the same amount to cool twice the house.

[TwinbrookNine]

2800 sq ft is WAY Different than 1800 sq ft. You better do it right or you'll "own Edison." like it or not.

2 units of course. Cold air falls. Let gravity do some of the work (personally I would never live in a two storey house in a hot place like that - and definitely not without a separate system for the second floor, especially with 2800 sq ft).