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Improve Central A/C Efficiency - Set to 78 Degrees - $600 to $700 electric bill

Improve Central A/C Efficiency - Set to 78 Degrees - $600 to $700 electric bill


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Old 06-27-17, 08:53 PM
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Improve Central A/C Efficiency - Set to 78 Degrees - $600 to $700 electric bill

My house is about 30 years old (2-story, 3000 SQ FT) and has original windows in okay condition but I'm sure there is air leaks. The 5-ton A/C unit is about 20 years old. The duct work, blower, etc. is all original.

During the summer (southeastern PA) the weather is usually around 80 to 90 with high humidity. The unit is set to 78 but struggles to keep up and runs almost constantly to keep 78. On hotter days it cannot keep 78.

A new system is not in the budget. The air coming out of the vents is cold but hardly blows - if you place your hand 3 feet above the vent you cannot feel it blow. The filters have been cleaned.

What can I do to try and improve its efficiency? During the month of August the electric bill can hit $600 to $700 which I believe is high for setting it at 78.

What should the central A/C bill be around for a 2-story, 3000 SQ FT at X degrees?
 
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Old 06-27-17, 10:55 PM
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Turn off power to the outdoor unit and rinse the outdoor coil. The outdoor coil should be rinsed once per year and can appear to be clean even when very dirty.
You don't want to bend the coil fins but you want to rinse until the water comes out clear on the other side of the coil.

Inspect the indoor coil. If it it is dirty it is usually very obvious unless someone has recently tried to clean it.





If this is a horizontal application cleaning isn't usually terribly difficult.




If this is a vertical application it is usually too difficult for a DIY project.




Verify that you do not have a return air duct leak or a broken supply air duct if you have access to the ductwork.

Grab the large copper pipe at the outdoor unit. Is it beer cold when the unit is running?
 
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Old 06-28-17, 01:59 AM
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is about 20 years old
electric bill can hit $600 to $700
A new system is not in the budget
A 20 year old AC system is beyond sustainability, you have the budget but are spending on electricity during cooling months and most likely the furnace is just as inefficient in the heating months.

From experience with having replaced my parents 15 year old system you would probably save 50-60% which would pay for the new equipment and maybe even some left over to address windows or other weather proofing items!
 
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Old 06-28-17, 05:12 AM
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With a bill that high I would suspect an electric heat unit and a stuck heat sequencer.
 
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Old 06-28-17, 06:54 AM
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The final solution: Move to a new house. I did that 3 years ago. That cut my AC bill from $380 to $150 (July) in Texas.
 
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Old 06-29-17, 10:28 AM
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From experience with having replaced my parents 15 year old system you would probably save 50-60% which would pay for the new equipment and maybe even some left over to address windows or other weather proofing items!
won't save anything near that unless there's a real problem with the existing equipment.

20 year old ac will be at least 10 seer and the heat 6 hspf or 80% afue. saving 10 to 30% is more realistic.

--------------

A 5 ton unit should be able to hang meat in a house that size and climate, and you should be getting very good airflow. (high cfm relative to sq ft)

Something is seriously wrong.

Is it a heatpump?
where are the ducts located? where is the air handler or furnace located?

How many kwh per day are you using in the summer?

Start by checking for dirty filters, blower wheel, dirty indoor coil if u have access to the underside of it.
 
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Old 06-29-17, 01:03 PM
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The insulation of a 30 year old house simply can not compare to a new energy saving home built Today. You can easily get 30% saving because of the new house (may be more, depends on where you are). Plus the new AC, that will get you another 30% saving, So, a total of at least 60% saving is reasonable. If you want to purchase a new house, make sure get a Energy Saving home (must have the Energy Saving Seal, Builder will pay the extra expense if your bill is more then some fixed amount , in my case, if my electric bill is more then $180, builder will pay the extra for the first two years). My old house is about 27 years old at that time, My old AC was 8 seer, my new house is about the same size (2900 sq ft)., new AC is 15 seer. So, with these numbers, you can figure out yourself.
 
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Old 06-29-17, 03:18 PM
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yah, buy a new house to save on utilities, great plan.

how long will it take for the savings to offset the realtor commission, lawyer, land transfer tax, movers? 50 years?

it's about the dumbest advice i've ever seen posted on the net.

you don't know anything about the house either, if it's 2x6 construction rather than 2x4 savings of a new house would be minimal, equipment aside.

i suppose fixing the problems with the equipment or ducts or envelope is out of the question.

seer ratings don't mean much if things aren't working properly. a 10 seer from '96, properly operating, won't cause $700 utility bills unless the rate is very high or something is wrong.

post 1992, the minimums became 10 for cooling and 80% for heat - not that bad.
 
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Old 06-30-17, 09:40 AM
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New house suggestion looks dump, and of course there are many expenses, but that is not the point. All I went to show here are the numbers. from a poor insulated old house to a new energy saving one, plus all the new systems, you can save a lot. These are common sense, but I just want to show some real numbers to support the fact. (by the way, I don't think my post is that dump, at least not to me, because I am a new house builder)
 
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Old 07-02-17, 04:44 PM
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In situations where you have high humidity problems the new high SEER units with smaller capacity compressors too often can't pull the evaporator pressure & Temp down enough to lower the indoor humidity which leads to very long runtimes & lack of comfort.

The 10-SEER units actually work better than 13 & higher SEER units where there is a lot of humidity to deal with...the higher SEER longer runtimes won't save you much 'if any' on your utility bill.

To cool effectively you need a lot of airflow with 5-tons of cooling which it doesn't have now (fix airflow)...!

Also see post #4, & make sure there are no Return Air leaks from the attic, etc.
 
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Old 07-03-17, 08:09 AM
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Dealing with Low Airflow - Optimizing the Supply Air CFM Volume to the Rooms

You always want the highest static pressure on the supply side at the diffusers to the rooms, while at the same time reducing as much ‘resistance’ or pressure drops in the rest of the supply side as possible, which also includes low pressure drop fittings in all of the supply side ductwork.

You want to greatly reduce the airflow ‘resistance’ on the return side to produce more static pressure in CFM airflow on the supply side.

Reducing all the return air ‘resistance’ possible on the return side making any ductwork optimally as large as possible, plus return air filter areas as large as possible to reduce all return resistance in pressure drops possible which will maximize and optimize supply air CFM both to and from the rooms.

Edit: Make sure the indoor blower wheel & evaporator coil are CLEAN...!

Get at least 1750-CFM with that 5Ton system...!
 
 

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