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Install & Replace

Replacing AC unit - how much electricity will be saved?

I know this is not the season for air conditioning.  But here in Texas, it got up to 112 deg for several days.  I had electric bills that were nearly $500 for 4 months and my AC ran 24 hours a day.   I do not want to live through that again.  My home and air conditioning unit were built/ purchased in 2004.  I feel that the unit is undersized but most contractors have disagreed because they are going by some EPA recommendation.  The unit is a 3 ton Carrier, I think 8 seer.  The home is 1987 sq ft, two story. 


Here is my quesiton:  How can I determine how much electricity will be save if I upgrade to a 4 ton 13 seer unit?

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Posted 2011-12-20T16:51:01+0000  by kjar kjar

Hello Kjar.  Welcome to the community.


I remember seeing news reports last summer about the truly smoking hot weather down south.


Since you have SEER, (Seasonal Energy Efficiency Rating), ratios for both old and new units, a rough estimate is fairly easy.  The new larger unit will hopefully not have to run 24/7 like your current one does.


Based strictly on output per watt of power in and assuming all other conditions are the same, the new A/C will use about 8/13 as much electricity.  This is about 38% less energy use.


Hopefully next summer won’t be as hot either!


I hope this helps,


Posted 2011-12-20T17:31:28+0000  by Chris_HD_CHI

In November 2010 we replaced a 4 ton Lennox 1992 8 seer with a 4 ton XR 15 Trane 16 seer (including compressor, air handler and UV lights. Under air we have 2045 SQ feet (two story) Cost installed was about $4600.00


After installation the KW usage dropped so dramatically the Electric company sent out a meter reader to check  :-)


In Florida the hottest months are usually July-August-September

July -August 2010 temps were an average of 90 degrees,  we used 3353 KW hours that month.

In comparison the July -August 2011  KW hours usage at average temps of 93 degrees was 1842 KW hours.


My last bill received was $132.00 with budget billing as opposed to the average of  $300.00 we were paying prior to installing the new unit.


Made a big difference, you will notice it within 30-60 days.


I hope this helps.


Good luck!



Posted 2011-12-20T17:42:06+0000  by floridalife57

THank you for the info.  My high kilowatt usage was Aug 4-Sep 5 at 4712.8 kwh. If I am calculating correctly, 38% less kilowatts, that would be around 2929 kwh.  So that would be good.  Thanks again.

Posted 2011-12-20T18:24:51+0000  by kjar

Thanks Floridalife57.  You gave me even more good information with the numbers on the kw usage.  From Aug 4- Sep 5 we used 4712.8 kwh and Sep 6-Oct 5 3859 kwh.  If I can reduce usage like you did to 1842 kwh, I would be happy. 



Posted 2011-12-20T18:28:48+0000  by kjar

Newf - is the calculation you are using 8/13 referring to the 8 seer vs 13 seer systems?  So if I get a 15 seer the calculation would be 8/15 ?  Thanks in advance for the info.

Posted 2011-12-20T18:30:47+0000  by kjar

Hey Kjar.


Yes.  Mathematically, comparing pure ratios the numbers work out that way.


Going from 8 to 15 you would use 8/15 as much power (53%), saving 47% compared to what you used to use.


While your mileage may vary due to real world factors like fan motor run-time, changes in weather from one year to the next, etc. the savings are still substantial.  floridalife57's real world examples show the energy savings.


I should add that anywhere you can improve on insulation will also reap rewards.

Programmable thermostats can also help when there are periods of time the home is unoccupied.



Posted 2011-12-20T18:59:44+0000  by Chris_HD_CHI

Hello floridalife57 and welcome to the Community! We are glad to have you join the forum.


Thanks for the real world information on your energy savings.

Let’s keep the meter readers busy. :smileytongue:


Please keep us updated on your projects and feel free to join in helping others.


Posted 2011-12-20T19:06:45+0000  by Chris_HD_CHI

Hi Newf,


Is it better to replace the AC Unit during the fall and winter months? If so, what are the advantages of doing so?




Posted 2011-12-21T15:40:35+0000  by CraftyGalDIY

Hello CraftyGalDIY.


The only advantage I can think of is that in the "off" season you MAY be able to get a price break.


While the same people that install A/C units generally also do furnaces, there is no hurry to install an A/C unit now in much of the country.  As a result, the install can be timed when crews are not busy.  Add to that the occasional clearance sales from manufacturers at this time of year and there is at least the potential of saving some money.


Also a cost issue, if you need to replace your furnace then adding in a new A/C unit at the same time can result in some savings.


I hope this helps,






Posted 2011-12-23T14:15:19+0000  by Chris_HD_CHI

Hi Newf - I am still planning this project and I am down to deciding on heat pump or electric furnace to go with my new AC.  Can you tell me which one uses less electricity?  Heat pump or electric furnace?

Posted 2012-03-31T09:49:07+0000  by kjar
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