Air Conditioning / Bigger AC or Better Insulation

Air Conditioning

We ran the numbers based on the San Marcos, Buda, Kyle, and New Braunfels air conditioning weather data using a rather average 1000 square foot home with an existing R13 attic insulation. We assumed a 12 cent per KW electrical cost and a 1 dollar a square foot cost for adding R19 attic insulation.

The first $1000 we spent on attic insulation took us from R13 to R32 and reduced the size air conditioner we needed by only 2851 Btu’s.  Based on a 13 SEER air conditioning system our estimated annual utility savings would have been $74.00.  At that rate, it would take 13.5 years to get our $1000.00 investment back.

Then we spent another $1000.00 to take our R32 attic insulation to R51. The additional insulation only reduced the size of the air conditioner needed by 913 Btu’s this time.  The additional estimated utility savings was now only $24.00 per year. At this rate, the second $1000.00 would take 41 years to return our $1000.00 investment.

Having added a total of R38 attic insulation only decreased the air conditioning load by 3764 Btu’s or slightly more than ¼ of a ton for an additional cost of $2000.00

The first thing that becomes apparent is the law of diminishing returns. The first batch of R19 attic insulation was much more cost effective than the second batch of R19 attic insulation.

All these numbers got us to wondering what would happen if we took our imaginary 1000 square foot home and spent an additional $1000.00 to install a 15 SEER air conditioner instead of a 13 SEER air conditioning system.  Our estimated annual utility savings on the more energy efficient 15 SEER air conditioner was $142.00. The higher SEER system returned out $1000.00 investment in just 7 years.

City and utility company rebates for adding attic insulation could make a big difference on any final decision.  If you do the work yourself, you can certainly add R19 attic insulation for less than 1 dollar per square foot. Attic insulation isn’t everything. Insulation only slows down how long it takes the heat in the attic to work its way into the house. A big opportunity to save money on utility costs in the San Marcos, Buda, Kyle and New Braunfels area is to make sure your attic never gets overly hot by seeing that it is vented correctly.  Taking a summer attic from 160 degrees to 120 degrees on a 100 degree day will do wonders increase the effectiveness of your existing attic insulation and to lower your utility bill.

If done wrong, attic venting and powered vent fans can cause more problems than they solve. Contact an AirOne professional and we’ll be happy to help.

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