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maydaymay 08-06-2012 01:57 PM

Do I need a 2-stage AC in Arizona?
I am in need of replacing an old Trane XR12 that hasn't been cared for (just bought a used house). We are in Arizona where its REALLY hot and REALLY dry in the summer months, but during the mild spring months we leave windows open quite a bit. The transition time between cold and hot months is pretty short.

My question is will I benefit much from a 2-stage unit in terms of comfort and energy savings? I imagine that most of the time during the summer the unit will be running at full capacity.

Of the various units we are considering the 2-stage are pricier and don't work with the Nest thermostat we have (that's not a deal breaker though).

Other relevant info:
Home size is 4000sqft
2 AC existing units (Both Trane XR12, 4 ton and 5 ton). The 5 ton unit is on the West end of the house and still good.
The unit to be replaced is on the East end of the house and gets minimal afternoon sun.

Thoughts apprciated.

Doc Holliday 08-06-2012 03:29 PM

You're going to notice a drop in energy consumption due to seer rating alone. Minimum made now days is 13 seer. If you go 14 seer single stage you'll notice a considerable drop in electrical usage as it is.

Around here in Houston, I've installed single stage 14 seer R410-A systems and people's energy bills have dropped in half. Remember, the old systems which are being replaced are no more than 11 seer.

Outside of that, Arizona being dry I'd doubt you'd need to dehumidify the air which is basically what low speed would do concerning the blower.

You can also buy an upgraded single stage x-13 blower motor for your furnace and drop your bill even more.

gregzoll 08-06-2012 03:32 PM

You can set a two stage for single.

scottmcd9999 08-06-2012 03:54 PM


You can set a two stage for single.
What would be the purpose of doing that?

turnermech 08-06-2012 03:58 PM

4 and 5 ton size two stage unit don't achive that much more of a SEER rating than a single stage. The model line may have SEERs as high as 19 in the litaure but these are achived most always with 3 ton and smaller.

Before spending the extra coin on 2 stage make sure you are looking at AHRI certificate (goverment ratings) for the actual equipment you are purchasing. I find that with the larger units (4 ton and expecially 5 ton) the SEER ratings don't increase that much but the price does. There is also another number to consider with a/c an that is EER it dose not increase much on 2 stage units in the larger size either.

maydaymay 08-07-2012 11:34 PM

After getting several quotes and looking at different units we decided to go with the Lennox XC21, which is a 2-stage system. Between Lennox and our power company there's $2300 in rebates which puts is less than the single stage unit we were considering.
Thanks for all the input.

bobinphx 08-07-2012 11:45 PM

ok,,, go with a dual speed, but do yourself a favor have a manual j and manual d done (use some of that 2300 buck rebate!!).... this will make sure that you get the right size and that too will save you money. also, in phoenix, in the spring and fall, you can run an evap cooler.. so you might want to look into that too... just do yourself a favor and have a separate duct system run for the evap....

bottom line is that your really can save with a correctly sized and correctly installed system ... do some reading on static pressure and return air sizing....

beenthere 08-08-2012 04:36 AM

5 ton XC21. Whats that get, around a 16.5 SEER?

There re many 14 SEER condensers that when matched to a VS blower with the right coil that will get 16 plus SEER.

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