Is upgrading home AC a thing? Or is AC capacity relative to sqft a fixed thing?

2,676 Views | 29 Replies | Last: 2 yr ago by Ghost of Bisbee
lancevance
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Do people upgrade their AC to make it colder? Or make it colder faster? Just a random question. My ac is working fine.
Texasyankee
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I would like to know this too. Our a/c works, but it seems to run an exorbitant amount of time when the mercury goes above 90.
george1992
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I replace our HVAC unit every other year. I hate being at a party and someone asking what seer our AC is and not being with the latest. I pride myself in winning every pissing contest.
txags92
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lancevance said:

Do people upgrade their AC to make it colder? Or make it colder faster? Just a random question. My ac is working fine.
I am far from an expert, but a not insignificant number of builders will undersize the AC units as a way to cut costs on a house. My understanding is that the loose rule of thumb is to size the unit at 1 ton per 500 sq ft. So lots of builders will do stuff like put a 4 ton unit in a 2450 sq ft house. Or undersize the intake so that the system doesn't put as much air across the coils. It isn't uncommon for HVAC companies to recommend up-sizing the intakes or duct work to increase the air flow or to upsize the outside unit to address the corners cut by the builder. Sometimes it is a real issue and will make a real difference, other times it is just BS to make more money off of a sucker customer.
Leeman
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Asking questions without showing a pic of large cans ?
riverrataggie
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I just redid my 5 ton and 3 ton units, HVAC, ducts, etc.

They were both about 20 yo and one went out.

I will say this. It is way more efficient and cools down much quicker. That said, they were ~20 yo units.
wbt5845
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I replaced both my old R22 units since they were leaking refrigerant and it was $$$$ to keep adding it.

New ones can really cool the house fast, but are a little loud since they're so much bigger.
42
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You may also want to take a look at your insulation and roof venting. If your soffits are blocked or you don't have adequate venting to remove the hot air in the attic, then that heat is going to work its way down into the house, causing A/C to work harder.
80s Guy
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Have we totally forgotten about rule 1 for an answer?
YellAgs
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I need humidity control when I upgrade mine. Living near the coast schweats balls
Tomdoss92
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riverrataggie said:

I just redid my 5 ton and 3 ton units, HVAC, ducts, etc.

They were both about 20 yo and one went out.

I will say this. It is way more efficient and cools down much quicker. That said, they were ~20 yo units.
we have a 22 year old 5 ton and a 9 year old 3 ton. 5 ton has given us no problems 3 ton is a lemon. well it still works just needs about $700 every year or two.

if you don't mind me asking, did you redo the whole system into a more modern single unit or keep the dual units?
any idea on energy cost difference or too early to tell?

azul_rain
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Depends on how big your wife's tits are ?
you may all go to hell and i will go to Texas
Martin Q. Blank
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Texasyankee said:

I would like to know this too. Our a/c works, but it seems to run an exorbitant amount of time when the mercury goes above 90.
That's not a bad thing. You want to size the A/C so that it sufficiently cools the house by running continuously on the hottest day of the year. They're more efficient than constantly cycling.
permabull
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It might be how it was set up but my parents got a bigger AC unit and it made things worse. It is feast or famine... so it gets uncomfortably hot because it runs so infrequently the humidity is high and then when it clicks on it gets way too cold.
42
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They need to check the temp variance in the thermostat,.between where it cuts off and on. Have it at about a three degree variance, it will run more often, but not warm up as much before it turns back on. Plus, the more often it runs, the more moisture it will pull out if the air.
riverrataggie
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Tomdoss92 said:

riverrataggie said:

I just redid my 5 ton and 3 ton units, HVAC, ducts, etc.

They were both about 20 yo and one went out.

I will say this. It is way more efficient and cools down much quicker. That said, they were ~20 yo units.
we have a 22 year old 5 ton and a 9 year old 3 ton. 5 ton has given us no problems 3 ton is a lemon. well it still works just needs about $700 every year or two.

if you don't mind me asking, did you redo the whole system into a more modern single unit or keep the dual units?
any idea on energy cost difference or too early to tell?




We kept dual units. To early to tell still.
Furlock Bones
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hypeiv said:

It might be how it was set up but my parents got a bigger AC unit and it made things worse. It is feast or famine... so it gets uncomfortably hot because it runs so infrequently the humidity is high and then when it clicks on it gets way too cold.
This is a real issue. People think bigger is better. No. Right size is better.
bmks270
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I replaced my AC a few years ago. It was my first go around on my first property.

Here is what I learned. AC is sized to the sq-ft of the home based on tons. This can be influenced by your insulation in the home, but basically the AC needs to be matched to the sq-ft and heat flux of the home.

If the AC is too big it will cool too fast and in humid climates it will not run long enough to dehumidify the air. It will also cycle on and off more frequently, causing the temperature to swing up and down more quickly.

If the AC is sized correctly, it will run for longer periods of time, which has the benefit of dehumidifying the air, and it also won't cool so fast that it constantly cycles off and on.

More expensive AC systems have variable cooling capacities they can operate at which can control humidity better, but for the more affordable systems, they basically operate at a single Constance cooling capacity, and it's bet for indoor comfort and electricity usage if they are matched to sq-footage and heat flux of the home.

My old system couldn't cool the house in the summer running 24/7 turns out the system was old and the condenser coils were corroded. The heat exchanger efficiency was terrible. I got the cheapest new system they offered and it cut my electric bill literally in half and cools spectacularly. That is due to being way higher efficiency than my old corroded system even though it was the lowest SEER and cheapest system offered.


And I once worked in an office that had a terrible AC system, and it was constantly too cold or too hot, it couldn't hold the temperature between 68-74. It was either below or above that all the time. It sucked.
The Fife
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Square footage has little to do with size of the system, you heat and cool cubic footage. Window size, type, orientation, shading, insulation, ... are the big driving factors here.

If you really want to get it sized right to to www.loadcalc.net and play around on that site some.
Ghost of Bisbee
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Somebody call EcoZapp.

That's the only way you'll get the right answer
Texker
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Load calc and quality install that includes air balancing make a huge difference. We invested in a 2 speed system at our prior house and it was a game changer in terms of comfort.
Cromagnum
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Furlock Bones said:

hypeiv said:

It might be how it was set up but my parents got a bigger AC unit and it made things worse. It is feast or famine... so it gets uncomfortably hot because it runs so infrequently the humidity is high and then when it clicks on it gets way too cold.
This is a real issue. People think bigger is better. No. Right size is better.


Yep. Guarantee they have humidity issues in their home too since the unit isn't running long enough to dry the air out.
Teslag
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We ripped out our central air system and just put large evaporative coolers in a window in every room. Best move we ever did.
lancevance
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Salute The Marines said:

We ripped out our central air system and just put large evaporative coolers in a window in every room. Best move we ever did.


Your house must be loud!

Why not those individual split units you see outside of US (and also in guard shacks and work trailers). Those get super cold fast. Only problem is cold air is limited to that room.
rwtxag83
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bmks270 said:

I replaced my AC a few years ago. It was my first go around on my first property.

Here is what I learned. AC is sized to the sq-ft of the home based on tons. This can be influenced by your insulation in the home, but basically the AC needs to be matched to the sq-ft and heat flux of the home.

If the AC is too big it will cool too fast and in humid climates it will not run long enough to dehumidify the air. It will also cycle on and off more frequently, causing the temperature to swing up and down more quickly.

If the AC is sized correctly, it will run for longer periods of time, which has the benefit of dehumidifying the air, and it also won't cool so fast that it constantly cycles off and on.

More expensive AC systems have variable cooling capacities they can operate at which can control humidity better, but for the more affordable systems, they basically operate at a single Constance cooling capacity, and it's bet for indoor comfort and electricity usage if they are matched to sq-footage and heat flux of the home.

My old system couldn't cool the house in the summer running 24/7 turns out the system was old and the condenser coils were corroded. The heat exchanger efficiency was terrible. I got the cheapest new system they offered and it cut my electric bill literally in half and cools spectacularly. That is due to being way higher efficiency than my old corroded system even though it was the lowest SEER and cheapest system offered.


And I once worked in an office that had a terrible AC system, and it was constantly too cold or too hot, it couldn't hold the temperature between 68-74. It was either below or above that all the time. It sucked.



Nope.

Square footage is important, but only one of many factors. The professional uses what is called the Manual J, which takes into account Square footage, number of floors, which way the house faces, number, size, and type of windows, type of insulation and how it's applied, along with other important information. It's all put into a complex algorithm which tells you what kind and size unit you need.

Believe it or not, the most critical part of a home for energy efficiency is the windows. Windows are the single largest point of energy gain or loss in a home. Getting this right is the most critical thing if you want a lower bill and higher comfort level. More important than the system, insulation, radiant barriers, anything.

You DON'T want a unit that is too big. You are asking for trouble with a unit that cools too quickly and has to turn on and off frequently. It creates condensation issues in multiple parts of your home which will inevitably lead to mold issues.

Think fuel efficiency in a car. You want one that runs steady and smooth. You don't want a gigantic motor to shoot it up to 100 mph and then turns off so the car can coast to low speed, only to repeat the cycle.
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TAMC11
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Cromagnum said:

Furlock Bones said:

hypeiv said:

It might be how it was set up but my parents got a bigger AC unit and it made things worse. It is feast or famine... so it gets uncomfortably hot because it runs so infrequently the humidity is high and then when it clicks on it gets way too cold.
This is a real issue. People think bigger is better. No. Right size is better.


Yep. Guarantee they have humidity issues in their home too since the unit isn't running long enough to dry the air out.


Yea this is my understanding as well. Oversized units generally lead to humidity issues. The unit should be sized according to volume and load.
rwtxag83
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BTW, sorry if that came off wrong. Your post has a lot of good information; my contention was with you saying it's about Square footage.
Greater love hath no man than this....
bmks270
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rwtxag83 said:

BTW, sorry if that came off wrong. Your post has a lot of good information; my contention was with you saying it's about Square footage.


I did say heat flux and also mentioned insulation. Heat flux is a function of your insulation and is going to change depending on the home insulation, windows, shade, etc.

Win At Life
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Most home builders will guarantee a 20 degree delta. Meaning if it's 95 outside, you can do 75 inside. But it also means when it's 102 outside, your house is not guaranteed to cool to less than 82. It might do better, but not guaranteed.
74OA
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Ensuring air ducts and returns are correctly sized so the air handler can easily move the necessary volume helps reduce run time. Maintaining attic duct insulation and changing the air filter regularly are important, too.

Most air handlers have three fan speed settings. A higher setting forces more air more quickly thru the ducts, particularly to upper floors, and reduces run time.

Making sure your outside unit has at least a foot of clearance all the way around it to breathe and is completely unobstructed on top will reduce run time. Clean the fins with your water hose a couple of times a year.

Having an air return on each floor, or several in a large single-story house, is important to balance temp throughout the house and reduce run time.

Leaving the fan set to "on" or "circulate", helps constantly balance hotter and cooler zones and reduce run time.

Simply closing the blinds on the sunny side of the house helps a lot, as does applying 3M window film.

There's many small things that cumulatively help a lot before resorting to buying a larger unit.
Ghost of Bisbee
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