Needed expert HVAC advice

I am hoping some of the folks in atl.hvac will reply. I lerned the hard way not to post home-owner qs there. Here is the deal
Received two very different opinions of my a new HCAC proposal 1) stated that an oversized 4 ton Maytag with a varaible speed fan would be good for my updatirs. The problem is the air is not adequatly moving and the system runs and does not bring down the temp quickly. Goodman unit 3 ton with on small return sheet rocked over (fixed now).
2) Anoither HVAC tech agreed May is good stuff, but strogly objected to oversizing with the 4 ton unit. Stated it would constatlyy come on and off thus incresing the electric use and not dehumidifing.
ANy way to tell who is correct. My first HVAC person, whom I trust and has done work for me in the past repsectfully suggeted that the econd tech did not fully understand the varible speed.
Both were going to redo some duct work to make move the air better
Any thoughts (Spell check in on the blink, pardon the spelling)
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Ok..you got one..

Ok...oversizing NEVER works. If it gives you an idea, I have one job right now that the owner oversized a couple of years ago, and is now involved in a $45,000+ mold issue...

Maytag makes a good washer. And he is right about the dehumidification. Oversized units short cycle, and do not remove humidity, as they are designed.

VS motors on an oversized unit will wreck havoc on the outdoor unit, and your home. It is VERY easy to determine what is wrong.
First, has EITHER of them done what is called a manual J? IF not, then neither has been able to perform a manual D....so read on.

Manual D, and cant be done till a proper manual J is done.
Look...while its hit and miss on problems over the net one thing stands true...there are NO rules of thumb in HVAC. If the contractors you are using, and talking to now do not know how, or why, or try to talk you out of the manual J, and D, showing you and explaining the results, fire them. End of story. The unit, sized to the home, with properly sized and installed ductwork, will be what you want. No guesses, no wild ass thoughts thrown into it. This is a prime example of the kind of work we get called in to fix. You try to save a buck, and it costs you 10.

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This is Turtle.
With only the imformation that you have given here. There is no way that any HVAC man can give you a respectiable answer in any form. There is no Manual J or D , Is it gas or heat pump, What is the square footage of top and bottom levels, What seer rating is the old and new equipment being talk about, What was the problem that started you to want to start all this work on the system, is this on a new home starting from scratch or changing out equipment already there, and last of all your wanting to put a 4 ton cooling system on a 3 ton cooling ductwork system , I think, with a veriable speed blower on a 4 ton tring to ram the air through a 3 ton ductwork is the last thing on this earth i would do. The Veriable speed blower have their purpose but asking one to do the above is asking for trouble. The veriable speed blower will run at 110% to maybe get you by but it will give you hell in the future. VS blower are not designed to run at 110% all the time.
Now what CBHVAC said about a screw up waiting to happen for the real HVAC company to come fix is exactly what is taking place here. Don't worry a bit here. When it screws up you will get tired of half fixing the systems and have to call a real hvac company in to fix it. Then you will get the right system to do the job you really want in the first place. Any hvac company that does not discuss the Manual J and D calculation with you when discussing the design is not to be talking to you as far as getting anything right the first time.
So here is your first beginning of info to get the system installed that will work. Get a Manual J and D on the system and discuss exactly what you want or size to have on the system.
TURTLE
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Ok, got it, Manual J and Manual D
THanks for your input, greatly appreciated.
Scott

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Ok, got it, Manual J and Manual D
THanks for your input, greatly appreciated.
Scott

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Scott:
SW> I am hoping some of the folks in atl.hvac will reply. I lerned the hard wa SW> not to post home-owner qs there. Here is the deal Guess they get a little snooty over there.
SW> Received two very different opinions of my a new HCAC proposal SW> 1) stated that an oversized 4 ton Maytag with a varaible speed fan would be SW> good for my updatirs. The problem is the air is not adequatly moving and SW> the system runs and does not bring down the temp quickly. Goodman unit 3 SW> ton with on small return sheet rocked over (fixed now). SW> SW> 2) Anoither HVAC tech agreed May is good stuff, but strogly objected to SW> oversizing with the 4 ton unit. Stated it would constatlyy come on and of SW> thus incresing the electric use and not dehumidifing. As the others stated, oversizing in this case is Not a Good Thing. not sure about the constantly on and off (my HVAC expertise is pretty much limted to changing the filter <g>) but the not dehumidifying is right. An oversized unit will not run long enough (key word is 'long'). BTW, don't you want to humidify the air in winter vs. taking additional moisture out?
SW> ANy way to tell who is correct. My first HVAC person, whom SW> I trust and has done work for me in the past repsectfully suggeted that the SW> econd tech did not fully understand the varible speed. SW> SW> Both were going to redo some duct work to make move the air better Rectangular ducts will pass more air than cylindrical ducts. Had an addition done two summers ago; when talking about the system in general the present capacity came up. We noted the Dining Room was always cool. Part of the problem was when that room was added by a previous owner they tapped existing round ductwork at right angles with round ducts. These sections were replaced with rectangular duct - much better!! :)
SW> Any thoughts (Spell check in on the blink, pardon the spelling) See you over in one of the Windows conferences!
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Dead wrong. Round ducts ALWAYS will flow more air than a square. Thats not sometimes, thats ALWAYS. You had a duct issue, that was creating an airflow problem.....thats fine, and easy to repair, but round, always beats out square, or rectangular, and thats a simple fact.
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