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Old 06-19-2013, 08:12 AM   #16
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Making 5 Ton AC unit 4 Ton unit


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Originally Posted by patrick eubanks View Post
i would ride that sucker til the wheels fell off then replace it with a properly sized piece of equipment. With a load calc. You may find that a 3.5-ton ac would be sufficient.

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Old 06-19-2013, 09:22 AM   #17
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Making 5 Ton AC unit 4 Ton unit


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someone being able to set the stat at 73 or 74 instead of 72, fewer start up using less wattage),
Ah, I see now! So, the savings comes from having the thermostat at 74 instead of 72, not because a smaller unit was installed.
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Old 06-19-2013, 04:26 PM   #18
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Making 5 Ton AC unit 4 Ton unit


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Ah, I see now! So, the savings comes from having the thermostat at 74 instead of 72, not because a smaller unit was installed.
Not always. Some people keep it at the same temp. And still save money.

You are over looking cycling cost.

Sorry, but its not a thing that you can figure out with pencil and paper, unless you understand how the system actually works to cool the house. And that is not intended to be insulting in any way.
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Old 06-19-2013, 06:29 PM   #19
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Making 5 Ton AC unit 4 Ton unit


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Originally Posted by Patrick Eubanks View Post
I would ride that sucker til the wheels fell off then replace it with a properly sized piece of equipment. With a load calc. you may find that a 3.5-ton AC would be sufficient.

My house was built in 1960 with the return ducts in every room, so it's very comfortable in every room with the temperature being equal throughout. R19 in the attic and the exterior walls have been pumped with installation. It's not a E300 house, but it is insulated pretty good. I'm also under shade trees in NC. I think the calculations show the need for 3 1/2 tons for my size house, but I'm thinking about going with a 3 ton 18 seer so it will run more, be quieter and I'll be able to use my generator to keep it going in power outages. My 5 ton does a great job, but it's over kill. The previous owner went big. It cycles for 12 minutes on 95 degree days with a total run time of 6 1/2 hours in a 24 hour period. I am assuming a 3 ton would do the job in 13 hours or less based on the calculations I've read about moving the air? I figure the benefits of a smaller unit are also the fact that longer run times will give me constant temperature in house for a longer time. My unit keeps my house more comfortable than my children's modern houses. I am able to set my thermostat higher than they are and my house is more comfortable. I assume that is because I have returns in all the rooms and my house had excellent duct work? My current 5 ton unit will put out 44 degree air when it's 95 degrees outside. The 120K heat unit puts out 120 degree air when it's 20 degrees outside. I'm actually afraid to buy a new unit because I'm wondering if they are as good as what I have. I realize they don't last forever and I was thinking I need to be ready to replace it whenever it starts having problems. What is the KW usage for a 3 ton 18 seer unit? I have been told my 5 ton is 7KW.

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Old 06-19-2013, 06:42 PM   #20
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Making 5 Ton AC unit 4 Ton unit


I want to be prepared when the time comes to replace my 5 ton with a properly sized unit. I heard about an AC guy that put a 2 ton unit in a 2200 sq ft. house and was pleased with the unit. He told people it more economical for the unit to run most of the time (due to start up cost and damage on the unit from starting so often) I understand this logic as long as the smaller unit will get the job done on the very hot days.

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Old 06-19-2013, 11:34 PM   #21
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Making 5 Ton AC unit 4 Ton unit


if you've heard of this guy than you'd be correct but the guy you've heard of is an hvac specialist. his envelope is tight and I'm sure his home his zoned.

does not matter the size of a unit, the start up is hard on a compressor regardless unit size or square footage.

heat load determines size for dwelling.
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Old 06-20-2013, 06:21 AM   #22
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Making 5 Ton AC unit 4 Ton unit


If the load calculation calls for a 3.5 then you need to install a 3.5. Here is the twist though. A 3-ton, 18-seer is a multi-stage unit and probably rated for 3.5-ton. Anyway, good luck with your decision when you need one!
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Old 06-20-2013, 07:16 AM   #23
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Making 5 Ton AC unit 4 Ton unit


What would the load rating be for a 3 ton 18 seer unit? 2.1 KW or less? Do the unit comes with the ability to manually set these multi stage units to run on the lower power consumption? Is the lower stage 66% capacity? And what would the load rating be on the lower stage 1.6KW
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Old 06-20-2013, 07:27 AM   #24
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Making 5 Ton AC unit 4 Ton unit


The usage requirements vary by manufacturer. Typically, I set up the run time for the unit from the thermostat. It starts out on low stage for three minutes and then switches to high stage as long as the temperature differential is greater than three degrees. Once the three degrees barrier is reached it switches to low stage. On most set-ups it rarely gets out of low stage. One thing to note is that in order to actually get 18-seer from an AC/furnace set-up, the furnace has to be variable speed and able to achieve the proper airflow. I doubt that you can achieve a 3-ton airflow with a 5-ton furnace. When you start looking at variable speed furnaces it can get really pricey really quick. Shop around when its time and base your decision on warranty and your comfort level with your contractor.
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Old 06-20-2013, 07:39 AM   #25
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Making 5 Ton AC unit 4 Ton unit


really all of this talk about rigging the unit so it only runs on low stage is nonsense. Size the equipment based on the load calc. and it is what it is. If your concerned about utilities then spend some time tightening the leaks in your house and ductwork or cut the thing off but I assure you if it calls for a 3.5 then a 3 will not do the job and end up running up your utilities because it will never cut off. multi-stage, variable speed equipment will get you the results your seeking as long as you have a tight duct system and the equipment is properly sized. To give you an idea of the impact equipment selection can achieve, I just installed a new 3-ton, 15-seer packaged heat pump with a new super tight duct system in a customers house. We removed a twenty year old, 3-ton packaged heat pump and standard duct system from the house prior to the installation. We foamed the holes under the house in the floor around the plumbing pipes and a few other places as well. Twenty minutes of foaming and a new system and we cut the customers KW usage in half. I live in eastern NC so our weather is not as extreme as some but the customers savings will still be a huge return on initial investment. Do your research, find a knowledgeable contractor and listen to what he has to say. consultations are usually free.
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Old 06-20-2013, 08:45 AM   #26
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Making 5 Ton AC unit 4 Ton unit


spend 8 grand to get a new unit, save $50/month average. think about how long the payoff will take. maybe you'll get a grand or two back when you sell the house, but it takes a LONG time to get ROI on a new HVAC system. plus, you have to consider insulation, windows, etc. etc. an older house just uses more juice to cool and heat it, period. if you want efficiency, you really need a new house or you need to burn a ton of money on a bunch of other stuff in addition to the HVAC. in this economy, it just doesn't pay, you'll never see that money back.

but hey, i'm not a real estate agent or an a/c salesman, i'm just a knowledgeable homeowner that does my own work to save money.
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Old 06-20-2013, 08:54 AM   #27
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Making 5 Ton AC unit 4 Ton unit


I totally agree with you. As I have said often, put the pencil to the paper and you will come up with the proper solution. I agree that the wise thing to do is to run the current unit until the end of its life. I also realize with a 22 year old unit that can be any day so I want to be ready. It's obvious this forum has some wise people on it with a wealth of knowledge for me to utilize. Your logic also applies to 18 seer verses 15 seer units. $1000 or more extra for the 18 seer unit will take a long time for the return in savings. There are lots of thoughts about the two stage units giving more trouble. I've heard some say get a straight 15 seer and not worry with the two stage issues that might arise later. When you figure repairs and initial cost the difference in savings gets much smaller. Comfort and reliability are the top factors to consider. There are lots of things to consider. I appreciate all the feedback. It certainly gives me more info in the decision process.
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Old 06-20-2013, 03:09 PM   #28
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Making 5 Ton AC unit 4 Ton unit


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Originally Posted by Patrick Eubanks View Post
really all of this talk about rigging the unit so it only runs on low stage is nonsense. Size the equipment based on the load calc. and it is what it is. If your concerned about utilities then spend some time tightening the leaks in your house and ductwork or cut the thing off but I assure you if it calls for a 3.5 then a 3 will not do the job and end up running up your utilities because it will never cut off. multi-stage, variable speed equipment will get you the results your seeking as long as you have a tight duct system and the equipment is properly sized. To give you an idea of the impact equipment selection can achieve, I just installed a new 3-ton, 15-seer packaged heat pump with a new super tight duct system in a customers house. We removed a twenty year old, 3-ton packaged heat pump and standard duct system from the house prior to the installation. We foamed the holes under the house in the floor around the plumbing pipes and a few other places as well. Twenty minutes of foaming and a new system and we cut the customers KW usage in half. I live in eastern NC so our weather is not as extreme as some but the customers savings will still be a huge return on initial investment. Do your research, find a knowledgeable contractor and listen to what he has to say. consultations are usually free.

He has a single stage A/C. Can't be "rigged" to only run in low stage.
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