Central air vs Attic insulation


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Old 07-12-11, 08:00 AM
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Central air vs Attic insulation

My mother states that she has to keep her thermostat lower to keep the house cool compared to her friends and their homes. She generally keeps it at 69 to 70 to feel comfortable where they keep theirs at about 78. The people that installed the air conditioning system told her she needs more insulation in the attic to keep from having to run the AC so low in temp. Is there any truth to this.
 
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Old 07-12-11, 08:13 AM
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The attic is certainly a good place to start looking, but there are many possibilities. Do you know how much insulation is currently up there?

Other details will help as well. How old is the house? What style house? How are the heating bills? Is the ac in the attic? Is the attic well ventilated?

Bud
 
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Old 07-12-11, 08:40 AM
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What temperature does the thermostat say the house is?

I would think an insulation problem would cause the AC to have trouble getting to and maintaining a low temperature setting, not require a lower setting.
 
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Old 07-12-11, 08:48 AM
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There is just enough insulation to fill the voids between the beams.

Home is a single story rancher I believe 1,600 sqft built in 1968

Winter bills for heating run about $110-$120 during peak cold months

Summer air conditioning bills run about $250-$260 during peak hot months

The A/C unit is in hall closet

Attic is ventilated by 3 turbine vents
 
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Old 07-12-11, 08:54 AM
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The temp has no problem getting to and maintaining what she sets it to

[/QUOTE]I would think an insulation problem would cause the AC to have trouble getting to and maintaining a low temperature setting, not require a lower setting.[/QUOTE]

Same thought i had. last I heard heat rises and with attic ventillation it shouldnt be radiating through the ceiling
 
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Old 07-12-11, 11:16 AM
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Fiberglass, the insulation of choice back then, does a poor job of stopping radiation, basically just a poor job. There should be a lot more something up there, being careful not to cover the soffit vents.

Here is the 1, 2, 3. Before you bury everything in insulation, pull back what is there, locate and seal electrical, plumbing and the tops of walls so conditioned air cannot escape into the attic. Make sure you have plenty of soffit venting as those turbines may be pulling good air from the house. Then at least double what is there to R-40 or better.

If the heat and ac use the same ducts, you can get a double win by sealing all seams. Specific problem areas are where the ducts pass through unconditioned spaces and panned ducts that use the wall cavities for returns. Returns that pull in attic air will kill your ac bills but not as bad for heating.

Air sealing and insulation.

Bud
 
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Old 07-12-11, 01:17 PM
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Those heating bills aren't bad Id say insulation is ok Id look at attic ventilation to help cool the attic. More insulation will do nothing for cooling.
 
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Old 07-14-11, 11:53 AM
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Humidity

The feeling of comfort relies on both the humidity level and the temperature. If the a/c system is significantly oversized, the indoor relative humidity will be higher than normal. For a return air temp of 70, the supply air should be 50 or below. If not, then either the a/c unit is lacking in performance or the airflow is too high. Either one of these scenarios will cause a lack of comfort due to high humidity levels. The indoor humidity should not be above 50% RH during summer months. Humidity is probably the reason that the house needs to be at 70 to feel comfortable.
 
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Old 07-14-11, 06:41 PM
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i wouldnt be looking at the insulation as the problem. your hot air is going to rise up into your attic anyway. heating bills are pretty low for a house that size. get a thermometer and see if the stat is still acurate. you may also have a system that was not properly selected. a house at 78 degrees with a RH of around 50% will feel much better than a cooler 70 degree house with higher humidity. when performing load calcs, contractors should select a system that cools not only sensible temp but also does a good job of removing latent heat (this is where your humidity is removed). if the stat is accurate, see if the indoor blower has mulitple speeds. factory is almost always on high. drop it down to medium, this will provide much more humidity removal and hopefully solve your issues.
 
 

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