A/C Condensing Unit size & blower motor


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Old 05-28-07, 02:04 PM
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A/C Condensing Unit size & blower motor

We live in a 2300 square foot home with high ceilings. The a/c is a condensing unit outside 3 ton, and a blower unit in the attic. It is 10 years old. I think it is about time to upgrade the system.

I think the 3 ton should be a 4 ton unit. Can I just replace the condensing unit outside with a new four ton unit or does the air return intake coils/blower motor unit thing have to be replaced also?

What is the average cost to have them both replaced? The a/c unit we have now barely keeps up during the summer months here in Texas.

What are the best brands? Thanks for any info.
 
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Old 05-28-07, 02:13 PM
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Unit size

You need to do or have done a manual J heat gain calculation. This will tell you how much cooling you need.

The indoor unit would need to be replaced as well, most likely even if you stayed with 3 tons, the indoor section woudl need to be replaced to get the increased efficiency out of the new outdoor unit. If you go to a larger unit, some ductwork may also be involved since you will need to move more air.

The best brand is whatever the best installer uses. I would rather have the cheapest equipment installed by the best installer than the "best" equipment installed poorly.

Costs vary widely from area to area & job to job to even begin to guess at a cost for your job.
 
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Old 05-28-07, 06:46 PM
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thank you for the excellent advice. so the equipment is about the same across the board as long as the numbers run the same..the best installer is the key.

I wonder how you find out who is the best installer? I know they have to be certified in Texas, but only for the freon capture, etc.

Ok, so I call up three companies and have them come out to give me a estimate on a new condensing unit and return air unit.
Even with an estimate I will not know if they are a good installer. dang. I used to be a property manager for 11 years and know it when I see it done. Yet what do you say in the middle of something you are purchasing...hey stop, you don't know what you are doing...

How much does it cost to have the J heat gain caculation done? Is it that important to have this done?

Makes me want to go to a/c school and get certified. Used to be engaged to a man and his family business was a/c. He taught me alot about the process of air flow and cooling, and also about "doing the job right". Extremely important. He did all the duct work in my old house and didn't fall through the ceiling or anything Miss him. He died a few years back 03 and young age of 37...

ok, focusing now. I will ask his Mom. She can ask hubby who owns the company. I don't live anywhere near there, so he can't do the work. Yet he might know someone here in town.

If you know how to pick a good installer let me know. I really don't know how to do that. Thanks again...Susan
 
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Old 05-28-07, 08:23 PM
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Wink

Might call the BBB there. Ask people around therewho they have work on there AC. Get 3 bids. They should run the heat loss and AC load on the home for you. Also check the duct work to see if it can take a 4 ton set up .Down there you might look into a heatpump.
go to http://warmair.net compare fuel cost for there

If you will stay in this home for the next 10 years. Down there might go for a seer of 15 are over . With that you can greet a tax credit from the IRS If you put it all in new you can get a 10 year warranty on all parts .
 
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Old 05-29-07, 11:40 AM
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The heat pump is actually in the system we own now. The previous owners did not like it at all. They completely had the heat pump wires and functions all disconnected. The heat is a gas furnace. No heat pump working and we don't want a heat pump. The cost of running the compressor for heat seems unnecessary here and the compressor being used more hours. WE barely have any days that are cold at all. The air conditioner runs year round here.

I think I should get the bids and information BEFORE my system breaks down. Since it is 10 years old, do you agree on getting bids and such now? It is a builder's model a/c.

Why does the air ducts and hoses make a difference with a 4 ton?
 
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Old 05-29-07, 11:42 AM
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Also, doesn't a 3 ton seem small for a house with 2300 square feet and 12 foot ceilings thoughout the entire house. The one we have now is seer 12. WE do want more seer.
 
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Old 05-29-07, 01:24 PM
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Yes, you should get bids before the system breaks down. After it breaks you will just want it working again and you will be much more suceptible to less-than-honest contractors.

The duct sizing is extremely important. Going from a 3 ton to a 4 ton is a 33% increase in cooling ability. The ductwork must be sized to fit the cooling needs of the house and the equipment. Ductwork for both cooling and heating is ALWAYS a compromise and if the current ductwork is too small the only way to have the cooling you want will be to increase the velocity of the air travelling through the duct. This increase in velocity will be noisy and will increase the pressures within the ducts and the pressure the blower must output which in turn requires a larger motor on the blower and more electricity to run the motor.

If the temperatures are such that you rarely need heat I personally would think that a heat pump would be ideal. At ten years of age the gas furnace is at least half way through its expected lifespan and you will likely need a complete new air handler anyway with the new A/C. Perhaps an electric "furnace" / air handler with the new A/C would be your best bet.

You simply cannot use the square footage of a house, even with the known height of the ceilings to estimate the necessary tonnage of the A/C. You need to have a heat gain calculation done.
 
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Old 05-29-07, 03:36 PM
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Thank you for all the information. I will consider everything you said and go look in the attic to see how the configuration of the air handler is done now. I have looked before, but not recently. Just replaced the hot water heater in the attic. That was easy except for the attic part

We have had a problem in the past with the a/c unit and I ended up fixing it when the "on-call" guy charged about $220 for his fee and a new thermostat. Was not the thermostat but a switch problem in the attic. Paid him anyway because he came out, put in a new thermostat, and it was on the weekend. Yet, the guy really did not know. He was so young his expressions alone gave me all the information I needed to know.

Have the a/c check - ups done and had a rusted out connecton repaired last summer. Reasonable price, service, and accurate.

I will call for a check up now and see where I stand on this unit.

What is the oldest unit you have ever seen still working?
 
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Old 05-29-07, 03:41 PM
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P.S. Actually when it is cooler weather here I just like having the fireplace going. It warms up the living areas just enough. I can sleep under the covers to keep me warm enough.
 
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Old 05-29-07, 08:01 PM
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Manual J--installer

You can download & run a manual J from here: http://hvaccomputer.com
The cost is about $50 & from what I have read, it is a very good program & has tech support.

Check with friends, family, co-workers, etc. about whom they have had do similar work & how well satisfied they were. Word of mouth is the best or worst, as the case may be, advertising a contractor can get.
 
 

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