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A/C runs alot - concrete block walls heating up

Posted by peabody1 (My Page) on
Sun, May 26, 13 at 8:19

We live in sunny FL. Our air conditioner runs alot. Our concrete block with stucco house sits in the sun. It seems like the concrete blocks heat up during the day and release the heat in the evenings. Even when it is cool outside our A/C will be running. I have had the A/C guy check the unit and everything is working great. It is sized appropriately, etc. I try to close the blinds on the west side of the house in the afternoons. We can't plant trees to shade the sides of our house because our homes are so close together. They put foam insulation in our blocks when the house was constructed and we even had the garage insulated, plus the garage attic plus insulated garage door. Our windows are Low-E windows. Our house has a very light gray roof and is painted a light color. I feel like our A/C wouldn't run as much if we could keep the sun off the exterior walls. Any suggestions would be greatly appreciated. We live in a community that has rules. So you just can't do anything you want. You have to get their blessing. But perhaps some of you have some ideas that we haven't thought of and they might approve of.


Follow-Up Postings:

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RE: A/C runs alot - concrete block walls heating up

The best source of information about energy conservation for your climate that I have seen is the Florida Solar Energy Center. See if there is anything on their site that is specific to your block house situation.

Try U of FL as well. Land Grant Universities usually deal with this kind of home economics problems. If no joy there, try states with similar climates and Buildingscience.com


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RE: A/C runs alot - concrete block walls heating up

aside from a/c running a lot..are there other issues?
comfort issues?
high relative humidity?
high utility costs?

it isn't a bad thing for the unit to run a lot, esp
in a hot humid climate.
long runtimes will allow the unit to dehumidify
which doesn't happen when unit runs for short times
off and on (short cycling)
long runtimes actually cost you less utility wise
running is cheap, it is start up that spikes elec
usage.
are your bills high?

even with foam inside of concrete block..there is
still a sizeable amount of the block that is just
masonary. concrete block has little R-value.
so if the block is 18" long then only 14-15" of it
has foam insulation. the concrete that isn't
insulated allows the heat to transfer through
the block. this de-rates the R-value of the foam.
the concrete block doesn't have a thermal barrier
to stop heat/cold absorption.

ideally between concrete block & stucco/plaster
there would have been 1" foam sheathing.
this is probably not the case in your wall structure.

low-e windows should be reflecting heat back out..
but what type of frame do the windows have?
metal will conduct heat, vinyl doesn't. if the low
e glass is surrounded by a metal frame..it is the same
as the walls..heat gain is through frames & it de-rates
the performance of the low e glass.

suggestions to block the heat??
plantation shutters for windows (if frames are metal)
free standing shading...think of antibellum homes
with shutters on porch..pergolas..awnings for west
side of house..

you say that a/c has been checked out & all is
fine..but did this include checking ducts for
leakage? you could be losing 30% of
conditioned air into attic via duct leakage.

the lighter the roof...the cooler the attic. but
what insulation do you have in the attic &
are ducts in the attic (although I assume they are)??

is this your first summer in the house?
what if any comfort issues do you have?
size of house? size of hvac system?

thats my 20 questions. post back & we will
go from there.

best of luck.


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RE: A/C runs alot - concrete block walls heating up

Block walls do OK until the heat gets high enough to penetrate through them before the temperature starts to fall at night.

If you have high enough temperatures to make it through the blocks during the day, the only way to reduce AC use is to add insulation.

I have lived in stone wall houses (16 inches of stone) in more temperate areas and the heat of the day never makes it into the house before evening.
The house stayed cool as long as you kept the windows and doors closed.
It cooled off enough at night well enough we made it through the whole summer without AC.
House stayed around 70 F with daytime highs into the low 80F range.


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RE: A/C runs alot - concrete block walls heating up

energy_rater-la,

I'll try to remember all your questions and answers them as best as I can.

This is our year round house for over 10 years. It has been the same issue ever since we had the house built. Yes, the energy bills are high. Unit runs even at night when it is cooler outside than what the thermostat is set at and the humidity will be low outside. As far as inside, the humidity is low. I have asthma and keep it low. The A/C guy checked in the attic and said the insulation was good in the attic and he checked for leaking duct work, but it was fine.

I keep the thermostat at either 78 or 79 degrees. I wear a jacket in the house because the air is so cold under the vent. It is just right for hubby. If I put the thermostat on 80 degrees, it is too uncomfortable.

The A/C has no problem cooling the house. It is like a refrigerator to me when it is set at 78 degrees. Just hate the big old bills. We see dollar signs every time it runs. And it seems to run alot. It is overcast right now so it isn't running. But on sunny days look out. And we don't like the fact that it runs when it is cool and low humidity outside. Hubby complains that is cool outside and the unit is running. So it has to be those concrete blocks radiating the heat back out at night. On a cooler day it will not run all day until maybe 4 p.m. or later.

The window frames are metal. We do not recall seeing any type of foam insulating board between the blocks and drywall.

We have about 1,650 sf. I can't recall the size of the unit. It was slightly oversized because we also have an enclosed porch (we call them lanais) that we sometimes cool or heat. The porch sits back into the house so it is surround by the bedroom, living room, and kitchen. Only one side faces outside. Faces north and is enclosed with windows and a door. The A/C contractor figured and gave us the size A/C we have. Said if it is too big it would not take the humidity out of the house.


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RE: A/C runs alot - concrete block walls heating up

energy_rater-la,

I'll try to remember all your questions and answers them as best as I can.

This is our year round house for over 10 years. It has been the same issue ever since we had the house built. Yes, the energy bills are high. Unit runs even at night when it is cooler outside than what the thermostat is set at and the humidity will be low outside. As far as inside, the humidity is low. I have asthma and keep it low. The A/C guy checked in the attic and said the insulation was good in the attic and he checked for leaking duct work, but it was fine.

I keep the thermostat at either 78 or 79 degrees. I wear a jacket in the house because the air is so cold under the vent. It is just right for hubby. If I put the thermostat on 80 degrees, it is too uncomfortable.

The A/C has no problem cooling the house. It is like a refrigerator to me when it is set at 78 degrees. Just hate the big old bills. We see dollar signs every time it runs. And it seems to run alot. It is overcast right now so it isn't running. But on sunny days look out. And we don't like the fact that it runs when it is cool and low humidity outside. Hubby complains that is cool outside and the unit is running. So it has to be those concrete blocks radiating the heat back out at night. On a cooler day it will not run all day until maybe 4 p.m. or later.

The window frames are metal. We do not recall seeing any type of foam insulating board between the blocks and drywall.

We have about 1,650 sf. I can't recall the size of the unit. It was slightly oversized because we also have an enclosed porch (we call them lanais) that we sometimes cool or heat. The porch sits back into the house so it is surround by the bedroom, living room, and kitchen. Only one side faces outside. Faces north and is enclosed with windows and a door. The A/C contractor figured and gave us the size A/C we have. Said if it is too big it would not take the humidity out of the house.


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