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Discussion Starter · #1 ·
I am having a new central heat and ac system put in. My outside unit is a 2.5 ton but needs to be a 4 ton. I have had at least 4 quotes and the last guy is a small operation, him and a a helper and he said he could do it for $4300. This includes a new return in my ceiling, 4 ton Gibson 14 sir unit outside and a new furnace. This was my cheapest quote, some other places in town go up to 10k but that is replacing all new duct. The lower prices are using my duct but making some adjustments. Any things to ask or look for would be appreciated.
 

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They have came in and got rough estimates, my unit has never cooled good. I am around 2000 square feet or so, my air return is also too small I am told and will be getting a new one. When it was working, it would have to run 24/7 and I would be lucky to get low 80's
 

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First, read here

https://www.angieslist.com/articles/difference-between-best-hvac-brands.htm

http://efficientcomfort.net/documents/Understanding_HVAC_System_Design_Issues.pdf

http://efficientcomfort.net/documents/Sizing_&_Selecting_for_Proper_Humidity_Control.pdf

http://efficientcomfort.net/documents/Bigger_is_Not_Better-Sizing_Air_Conditioners_Properly.pdf

www.loadcalc.net

You need to be certain that your issues were due to inadequate sizing, and aren't due to poor duct and/or performance issues with your current unit. Bigger is NOT better.
Second, if your home load calculation does show the need for 4 tons of cooling, then be certain that your duct can support such a load. You should be moving ~400 CFM/ton. Too little and you'll have reliability and life span problems with the unit.
 

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A 4 ton will freeze up on a duct system designed to handle 1000 cfm or less, or at best perform really inefficiently.

The sizing you've gotten from these contractors is beyond absurd unless you're in a brutal climate like phoenix, Arizona.

1 ton per 500 sq ft will get u into big trouble and it's BS dating back pre-1980 from when building science wasn't even a field and electricity was under 5 cents per kwh delivered all inclusive.

Where are you located?

2.5 tons is not at all out of line for a 2000 sq ft house at least from what I've experienced with ducts in the basement and decent insulation. Okay, you may need a bit more capacity with ducts in the attic, may need a bit more in a climate which experiences 95f+ more than a couple of days each year. Don't know about the construction either.

Wouldn't get more than 3 tons without an accurate heat loss/gain calc as well as major changes to the ducts. (which could be too small for what u have)

But the symptom of a marginally sized but well performing a/c is running continuously, having the temperature inside rise a few degrees above setpoint in extreme weather but otherwise cooling well and pulling out loads of humidity. (...and if it's pulling out loads of humidity having it drift up isn't such a big deal)

Bigger unit doesn't dehumidify as well and stresses the electricity grid more -> meaning forces the utility to build more peaker power plants, jack up the rate to cover for that.
 

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with city can look up the design temp, obviously u're pretty south so 90+ average july temps, high design temp.

there's a very good chance the that 2.5t is a bit undersized, but approach upsizing with caution, making sure the ducts can take the higher airflow and not going too large.

if you're knowledgeable with respect to construction and r-values, you can do a calc yourself. garbage in = garbage out though.
 

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I am in Arkansas
Doubt you need 4 tons. Maybe 3 tons. 3.5 if you don't have much insulation in your attic and or walls.

Your duct system is probably too small for the 2.5 ton you already have. And may be the reason why it doesn't cool very well. A 4 ton on that same duct system will be loud. You will have to turn up the volume on your TV and stereo to listen to them while it runs.

So very doubtful that anyone not changing out all of your duct work if installing a 4 ton system, is working in your best interest. Or too worried about your home cooling or heating properly.

Since its not real hot out yet. Turn your A/C on, and check the air temp at the return register, and the closest supply to the air handler.

What type of air filter have you been using. Your current return filter grille should be at least a 20x24.
 

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Discussion Starter · #11 · (Edited)
I have never had a normal working ac, it has always been very hot in my house and if you put your hand up next to a vent you could feel it blowing lightly. The outside unit broke down last fall so I cant test it. I think my filter is a 20x24 but I am supposed to get another return put in my ceiling in the hallway. I am supposed to be having another couple estimates, that will be a total of at least 6 and so far everyone has said they think I should be running a 4 ton. They have all went in my attic and seemed very thorough.
 

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But what about an actual load calculation? If the air isn't being distributed correctly then that's a duct issue, not an equipment size issue.
Please read and understand the links I provided. Bigger isn't better. In fact, if you put in an oversized unit you can have major humidity issues which can lead to mold and mildew growth. Undersized duct will cause worse issues then you have now.
 

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I will ask the guy I am leaning towards if he plans on doing a load calculation.

edit: I will make sure anyone who does it will
Just food for thought, but the follow responses of-

"I've been doing this xx years, I know what size unit you need"

"I put the same size unit in all these houses around here"

"You need 500 sq ft per ton"

"Load calculations are just stuff you do in school"

"I'm gonna put a unit in that'll have a little extra for those really hot and cold days"

-are all examples of guesswork and are NOT the proper way of sizing equipment. I cannot stress the importance of correctly sizing the equipment, and the duct that's attached to it. Even today, homes are still built with oversized equipment and undersized duct. My own home is like this.
 
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