Cooling a home with one or two units?

[tom1843]

I currently have a home in SE Florida of 1100 square feet. The tech did a load calc and said it would require about 3-3/4 tons to cool. I currenty have a 3.5 ton unit and it works good so feel the load calc is right. I am having a small addition be installed and the old one has to go. I know its a lot of cooling but its hot here and the house has an old 3/12 pitch roof which creates a very hot attic.

I asked about installing two units in the house and the company said they could do it. A smaller unit for the bedrooms and a larger one for the living areas. I figure why cool the rest of the house when its not needed in the evening, and why cool the bedrooms durring the day.

I like the split temerature control and I could save a lot of electricity which is getting expensive here.

Now, the power company said one cooling unit was more efficiant and less expensive. The cost of two units is not an issue, just being more energy efficiant.

I hope I explained everything ok. What are your opinions on this one or two units.

[amd]

3.5 tons is a hell of a lot for 1100 sq. feet. I suggest that you try to reduce heat gain before replacing the current system; smaller is smarter. (more efficient, better dehumidification)

[smokin68]

You could do two smaller systems, which actually sounds like a good idea, however I would invest in more insulation and better windows/sealing. At 1400 sq ft a 3 ton should be plenty(I'm also in hot Florida). An oversized unit won't remove as much humidity(definitely a must here). You will feel more comfortable at higher temps with lower humidity. I.E. a house at 72 degrees and 60% humidity could feel the same as a house at 75 degrees and 45% humidity( These figures aren't precise,just an example). A zoned system might be another option.

[tom1843]

I forgot to mention I also have a tar and gravel roof. I have new windows on order to replace leaky old ones. I have plenty of insulation in the roof. Power comapny paid for the insulation. All ceiling joints and electrical boxes are being sealed too.

The currnet system is a high velocity which works well at removing moisture. The house can be 79 degrees and you will say its cold. The HV system is being replaced because its in the attic and the new code (County requirment on upgrades)says it can't be there. In addition, the odd size prevnts me from using it in a new utility closet. Another thing is the hoses have some leaks and they real expensive to buy new for a relocation. It wasn't installed right either.

With the upgrades montioned above will two units work efficiently?

Thanks for your inputs.

[nina]

tom1843 wrote:
>1100 square feet

just to be aware that many of us live in S.Florida and I currently am able to maintain a 2000sq ft house with lake access on one side at 77F and <50% RH with just a 1.5 ton compressor (dual compressor Trane XL19i)

last 3 weeks (as you know) have been under 90F and rainy and I would only enable stage 2 (4.0 ton compressor) if temps went to 95F or above

don't oversize!

[beenthere]

If your keeping the temp at 79, I don't think you'll see any savings that will justify 2 units.

Have the load calc done including all the new improvements and see what size you need then.

[mjk_na]

Three things I would do:

1. Find out how I can reduce the heat gain even more.

2. Redo heat gain calculation.

3. Get a split unit with several evaporators for zone control, if split is the choice.

All the best.

[bornriding]

Unless you can completely seperate the two sections of yur home from one another, then two systems will cost more to operate than one system. One system will use less energy than two - I have done this before. We changed a customers two units for one unit ( the customer was skeptical ), but one year later he came to my office to show me his electric bills - 1 yr before and 1 yr after - he saved over $60/mo on his electric bill ( & the power rates had gone up ). Also I can't believe for 1100 sg ft, you would need over 2.5 ton total, which would be a savings in itself.

Richard