[MrSlottech]

My AC has taken a major dump. I have a rooftop unit and need a couple of answers to some questions.
My home is almost 2000 sq ft, What size should I replace with?
Currently a 3 1/2 ton RHEEM built in 1987. Since I have owned the home I added almost 400 sq ft to the home. Original build was in 1979. I have since sealed the house very well from the outside in, including sealing all the down holes in the framing for all the wires coming down. Also completely sealed the base of the home completely around the perimeter. I have also put dual payne windows in and also in the process of new exterior insulation and shear walling the outside and installing with 1" Styrofoam then stucco. (the home does not leak anymore when we have high wind days).

My cousin has worked for Trane for 20 plus years and he is recommending that I go with a 5 ton unit. His rule of thumb is a ton for every 400 sq ft. Is this correct thinking?

I know he can get me a really good deal for this unit as he has quoted me a couple of years ago and it was about $1500.00 less than I could get anywhere else. This will be a self install and getting the unit direct from Trane.

Now per the web and in our zone (Las Vegas area) for my size of home they are saying that I would need a 3 1/2 ton unit. Should I go by this or what my cuz is telling me?
Maybe a 4 ton?
Is a 5 ton a little over kill?

Any help or suggestions would be greatly appreciated....

Thanks

[yellowsnow]

AC is one of those things where bigger is not always better. With most units the biggest energy use is start up. So it's cheaper to have the right size that goes on and stays on for a while over a bigger unit that is always starting up and shutting down. Hope that makes sense.

I am sure that 3.5 tons is small for 2000sf. My home is about 1600 and I have a 5 ton unit but my power bills are much too high and I'm not at all sure that the 5 ton unit isn't too big. The most important thing is the efficiency of the unit. The higher SEER the better. And of course the higher the SEER, the more it costs.

Search the web, there are lots of formulas on right sizing AC units.

[Rhedrich]

I just had my ac and furnace replaced last week because existing one were on their last legs. They were original units from 1995. I have 3000 sq ft house single story house and I have a 4 ton and a 3 1/2 ton unit. The seer rating is very important I went with seer rating of 22. The unit also have the communication system with 2 thermostat that look like 2 iPad mini . I can also control them by my iPhone

[BBMW]

Find someone who can do a good, technical analysis (not a rule of thumb), and size the unit correctly.

[Rhedrich]

Originally Posted by BBMW

Find someone who can do a good, technical analysis (not a rule of thumb), and size the unit correctly.

I agree I had 3 contractor out to review, yes, Sierra and Sunnyside

[WestieJeff]

How well was your 3.5 ton system working? If you were happy with how it was working, I don't see a reason to upgrade. 3.5 tons is 3.5 tons, newer 3.5 ton units don't "cool" any better or worse than old 3.5 ton units. Granted, newer units will use less energy, but the amount of cooling they do is constant.

My 2000sf home has a 5 ton unit and there is no way I'd want anything less. I find it to be even a little weak on the hottest of days where it can really only bring the house down to maybe 77 during the hottest part of the day. That said, my house is not well sealed so that makes a big difference.

I still am surprised 3.5 tons is enough for you, but it depends on shading, window orientation, number of windows, etc.

[lvoc]

i go with WestieJeff. If your old 3.5 did the job don't go any bigger. You basically have done the experiment for what your house needs...Unless you found it wanting on very hot days you are there.

The only interesting question is whether you could go a little smaller but I would not bother. House is too large for any big reduction and going to 3.0 is probably an unreasonable risk of discomfort in very hot weather.

[jet757f]

Originally Posted by Rhedrich

I just had my ac and furnace replaced last week because existing one were on their last legs. They were original units from 1995. I have 3000 sq ft house single story house and I have a 4 ton and a 3 1/2 ton unit. The seer rating is very important I went with seer rating of 22. The unit also have the communication system with 2 thermostat that look like 2 iPad mini . I can also control them by my iPhone

You have 2 units for a single story house? I have heard of that for two level houses.

[MrSlottech]

Well my 3.5 ton didn't appear to be doing all that well of a job. The only time I would run the AC is when humidity was high. So it really didn't get run all that much. It is an old unit built in 1987 so the efficiency was not there at all. When it did run it seemed to run a lot especially this this summer. If I did not open a window on the opposite side of the house a little it would run ALL day long non stop!! The humidity dropped to good levels last week until yesterday so I went to turn on the AC and nothing but warm air. After checking it out I determined the compressor was froze up. So after some research and talking to a few friends in the refrigeration industry I have decided to go with a 5 ton unit. The 3 1/2 never really kept to what I would call a good comfort zone even at 78 degrees.

Thanks for all the reply's

[Rhedrich]

Originally Posted by jet757f

You have 2 units for a single story house? I have heard of that for two level houses.

Yes 2 units. The 3 1/2 ton cover the living room, dining room, foyer, powder room, master bed and bath(north wing) . The 4 ton cover the family room (vaulted) , kitchen, bathroom , large mud room , plus 3 bedrooms. (South wing). It more energy effencent when we have guest visiting we adjust the temp lower in the south wing and raise them when it just the wife and I in the north wing of the house. The house is long is long with the family room and the kitchen in the middle. We use the living room which is in the north wing more as our family room.