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Old 06-05-2013, 02:57 PM   #1
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I have an older air conditioner 3 ton and I am looking to replace it with a new unit.I know my unit is to small for the square footage of my home. I had a professional come out and do a load reading of my home and he stated I need a 3.5 or 4 ton. I went to a heating and cooling business in my area which is in the state of Ohio. I explained to the gentleman that when the temperature is in the high 80's and low 90's I set my air conditioner at 74 degrees it will steadly run for six to seven hours and never kick off. As the summer progress' and becomes more humid it will lose a degree or two. In the humid summer it will only cool to 74 and nothing lower. He stated this is normal. I do not know of anyone who has an air conditioner has this problem. Every person I know their air conditioner runs for maybe 20 minutes and kicks off. This fella says that you save money when it runs continueously. Does this guy know what he is talking about? I hope you HVAC guys can answer me honestly. I really would appreciate the answer to this. He is trying to tell me when I upgrade to a new air conditioner it will still do the same thing. Hope you all can help.

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Old 06-05-2013, 03:19 PM   #2
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Are you sure that it is a 13 ton unit? Do you realize how large a 13 ton a/c unit even is?

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Old 06-05-2013, 03:44 PM   #3
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maybe you mean 3 ton replaced by 3.5 to 4 ton. 13 might be SEER rating, but that is just efficiency, not cooling power.
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Old 06-05-2013, 05:04 PM   #4
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When its 98 outside, my A/C will run for 6 hours non stop, noon till 6PM. Trust me, if this was not correct, I would fix it. But I spent a lot of time tweaking it to get it to work like this.

The size A/C you need is not determined by the sq ft of your home. But by its construction.

A 2800 sq ft rancher generally needs a larger A/C then a 2800 sq ft 2 story.
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Old 06-05-2013, 06:50 PM   #5
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maybe you mean 3 ton replaced by 3.5 to 4 ton. 13 might be SEER rating, but that is just efficiency, not cooling power.
you are correct. I am sorry for the stupid mistake I made. I edited the wording hoping I can get the correct answer
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Old 06-05-2013, 07:30 PM   #6
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Do your own load calc to make sure you get the right size. If you have to increase the unit size then you/he needs to make sure the ductwork is large enough and the furnace blower can handle the extra size of the unit or it will freeze up from poor airflow. The reason yours runs non stop could be from a worn out compressor and low on Freon etc. A new unit of the same size may work just fine. Usually it should run no more than 20 mins on and then 20 mins off unless you wait till it gets warm in the house and manually turn it on. Then it could run for hours on end. I tell my customers to turn it on at 7-8 am in the morning and leave it alone and let it do it's job. Some don't listen and wait till 11 am when the sun is high and then it runs continuos.

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Old 06-05-2013, 09:59 PM   #7
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Yuri, you left out those, that get home at around say 7 or 8 at night, flip the unit on, set the temp to say 70, and it is 81 in the house, but wonder why it is only 80 two hours later. Then they post that it is around 96 outside with high humidity, and post that they shut their system off when they leave the house in the morning, because they do not want to spend money heating or cooling a empty house.

I finally listened to you Yuri & Beenthere, and have been leaving our thermostat at a set temp during the day and at night, but adjusted the night temp this year, after breaking in the outdoor unit, and getting used to having central air, and the 3m-50 in our place.

Found the best sweet spot for us was 70 at night, 72 during the day in the Summer, and 65 at night, 68-69 during the day in the Winter, but make minor adjustments during the Summer in night or day temp, depending on outdoor temps and humidity.

I finally turned our system back on, because of the storms rolling through tonight. It was 76.5 when I turned it on at around 7:30, it is 75 now after running about an hour. It has to of course cool down a 1640sqft home, but nice thing is, it is 68 downstairs, so with a return down there, it is pulling that cool air through, to help cool the upstairs better.

I know that there is one particular person on here that does not understand that I had my system sized due to the fact that we do not have insulation in the walls, but also that does not place a lot of heat gain or even cold loss on the system, because I have learned how to make the house work by fixing air leaks, and insulating the rim & sill joists down in the basement.

As for the OP and their sizing, they need to remember to get the glass window sizing, doors, all other info, or it is going to come out wonky. When I did it, it said 1.5 ton unit, and that was putting in even no insulation in the home, and both basement and upstairs factored into the calculations. The upping to a 2 ton actually worked out better for us, because the calculator did not take into account using the oven during the Summer, or that we have a Plasma tv in our living room, along with heat gain from the attic at that time, before we added the power vent to lower that temp.

Here in a couple years, I may end up just going with a Heat pump, because our Winter's have been more mild now than we expected at the time I was pricing out units, and only went with the a/c, because of costs.

So for the OP, figure out what you can afford, look at heat pumps vs. just a a/c, especially if your utility rates are going up for gas, like some are. We are seeing our delivery charges going up with Ameren this year, because everyone is becoming more efficient in their use, plus cutting back on running their systems, along with raising rates to modernize their systems.

Another thing, check around with local shops, especially small business owners and see if they can get a deal on a non-picked up unit sitting at the local warehouse, not one of those shops that gets kick backs from the manufacturer, because they push that brand and all they sell is one particular brand.

I have a Armstrong Air a/c, which is made by Lennox, and it is very quiet, compared to the Lennox unit that my next door neighbor has, that is around a 10 SEER. I measured our ambient noise on our unit, and at ten feet away, it was around 25db, next to it, it was around 42-45db.
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Old 06-05-2013, 10:26 PM   #8
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try NOT to run it when there are thunderstorms or lightning as that is when it is most prone to a power surge which will destroy the compressor. better to sweat it out for a few hours than have that happen. beenthere seen that happen many times I have.
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Old 06-05-2013, 11:14 PM   #9
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As long as the system is protected with a good surge protector on the panel, properly grounded for incoming service, and units are grounded it will not be a problem. It is when you are in an area that is notorious for poor power quality, or high lightening occurrences, then I wouldn't want to.

I have not had any problems with our unit for the 7 years we have had the furnace, and three for the a/c. I did get smart and put in a timer inline between the a/c & furnace, due to if power does trip, the unit actually starts up, because it does not have a timer built into the compressor, and the 3m-50 I found does not detect recycle on power, when you cycle through the thermostat from Off, Auto, Off, Heat, Off, Cool. Its internal software resets, each time it goes from a on setting, to a off setting. Brought it to RTCOA's attention when I got it, and they of course blamed it on our hvac equipment, not their product. Set the timer for an aprox wait time of 15-20 sec's, from when the furnace kicks on, before the outdoor unit cycles on.
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Old 06-06-2013, 12:08 AM   #10
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I cool my entire 1000 sq ft Iowa house with just a 5200 btu window a/c but then I have R100 insulation in the attic, an attic power vent fan, double pane windows and R22 +- walls.

What's the possibility of adding more insulation in your attic and an attic fan to reduce the biggest heat cauing problem at the source instead of trying to cover it up with a larger a/c?
If you added a good amount of blown-in insulation, and a power fan, you would notice a significant difference.
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Old 06-06-2013, 09:32 AM   #11
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Quote:
Originally Posted by worker903 View Post
I have an older air conditioner 3 ton and I am looking to replace it with a new unit.I know my unit is to small for the square footage of my home. I had a professional come out and do a load reading of my home and he stated I need a 3.5 or 4 ton. I went to a heating and cooling business in my area which is in the state of Ohio. I explained to the gentleman that when the temperature is in the high 80's and low 90's I set my air conditioner at 74 degrees it will steadly run for six to seven hours and never kick off. As the summer progress' and becomes more humid it will lose a degree or two. In the humid summer it will only cool to 74 and nothing lower. He stated this is normal. I do not know of anyone who has an air conditioner has this problem. Every person I know their air conditioner runs for maybe 20 minutes and kicks off. This fella says that you save money when it runs continueously. Does this guy know what he is talking about? I hope you HVAC guys can answer me honestly. I really would appreciate the answer to this. He is trying to tell me when I upgrade to a new air conditioner it will still do the same thing. Hope you all can help.
I'm an HO like you. Here is my story from Houston:

Bought 2 story 3600 square foot home, 1800 up and down equal dimensions. New home in 1998 and builder installed 2-3 ton units. Down worked ok cooling wise and heating was/is an issue. Up would run a lot on medium to definitely hot days and never feel good.

Had builder reinstall 2-4 ton units, and have never looked back. Yes costs a little more, but I know that I can turn it on and in a reasonable amount of time, the house will be cool. Also as GZ suggested, I stopped using the setback, it is cheaper for me to move it just a few degrees each way day and night.

Now for the not thought of stuff: return air and its placement.

UPSTAIRS: With the new upstairs system, we installed a new return in every room upstairs. All rooms can now close their doors and be comfortable if they chose to. Upstairs cooling issue no longer a problem regardless of temperature.

DOWNSTAIRS: Was not much we could do there, other than increase the size of the main downstairs original return air. Downstairs has 2 returns: a main in the ceiling (9ft) and a second in master bedroom. Would love to relocate this but have never figured out a way to get it from the ceiling down a wall.

The only problem that remained after all of this was the downstairs heating during winter. Due to high ceilings, open stairs and foyer to upstairs and in ceiling main return, it I hard to get the main living area comfortable without really cranking it up. Unfortunately, when it is really cold downstairs in winter, this unit cycles on and off quite often. Something that no one has been able to determine why. I am thinking now with wireless thermostats, of moving the stat and see what happens.

Like you, I was being told by the experts the same as you. These new systems would be overkill and the older ones were what the manual J called for, for my home. But in the real application process in my home they were not performing to what I wanted so I am glad I made them upsize.

I think you will need to step up and insist you get the system installed to how you want it to perform on the hotter days. Otherwise you will never be satisfied an up set with the HVAC contractor.

I know the experts will disagree, but what they will agree with is that the last thing they want to deal with is customer call backs because they convinced the consumer to change their mind and the system is not working the way they (homeowner) want it too.


Just my .02 as an owner.
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Old 06-06-2013, 10:13 AM   #12
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Sizing the AC close to the specs is important to keep it running longer which will give you much better humidity removal. Oversizing is OK if the ductwork and blower can handle it and if the customer is not fussy about humidity removal and just wants cold air fast. Where I am that is the case as our average humidity is rarely above 50-60% in the Summer. Humidity removal is not really a topic or concern where I am.
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Old 06-06-2013, 04:41 PM   #13
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Quote:
Originally Posted by digitalplumber View Post
I'm an HO like you. Here is my story from Houston:

Bought 2 story 3600 square foot home, 1800 up and down equal dimensions. New home in 1998 and builder installed 2-3 ton units. Down worked ok cooling wise and heating was/is an issue. Up would run a lot on medium to definitely hot days and never feel good.

Had builder reinstall 2-4 ton units, and have never looked back. Yes costs a little more, but I know that I can turn it on and in a reasonable amount of time, the house will be cool. Also as GZ suggested, I stopped using the setback, it is cheaper for me to move it just a few degrees each way day and night.

Now for the not thought of stuff: return air and its placement.

UPSTAIRS: With the new upstairs system, we installed a new return in every room upstairs. All rooms can now close their doors and be comfortable if they chose to. Upstairs cooling issue no longer a problem regardless of temperature.

DOWNSTAIRS: Was not much we could do there, other than increase the size of the main downstairs original return air. Downstairs has 2 returns: a main in the ceiling (9ft) and a second in master bedroom. Would love to relocate this but have never figured out a way to get it from the ceiling down a wall.

The only problem that remained after all of this was the downstairs heating during winter. Due to high ceilings, open stairs and foyer to upstairs and in ceiling main return, it I hard to get the main living area comfortable without really cranking it up. Unfortunately, when it is really cold downstairs in winter, this unit cycles on and off quite often. Something that no one has been able to determine why. I am thinking now with wireless thermostats, of moving the stat and see what happens.

Like you, I was being told by the experts the same as you. These new systems would be overkill and the older ones were what the manual J called for, for my home. But in the real application process in my home they were not performing to what I wanted so I am glad I made them upsize.

I think you will need to step up and insist you get the system installed to how you want it to perform on the hotter days. Otherwise you will never be satisfied an up set with the HVAC contractor.

I know the experts will disagree, but what they will agree with is that the last thing they want to deal with is customer call backs because they convinced the consumer to change their mind and the system is not working the way they (homeowner) want it too.


Just my .02 as an owner.
A 4 ton unit on duct work that may be under sized for 3 tons. Will only get you around 3 to 3.5 tons of capacity.

Often its not the size of the A/C. Its the under sized duct work that causes it not to cool properly.
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Old 06-06-2013, 04:48 PM   #14
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A 4 ton unit on duct work that may be under sized for 3 tons. Will only get you around 3 to 3.5 tons of capacity.

Often its not the size of the A/C. Its the under sized duct work that causes it not to cool properly.

Thanks, they used one of those fancy hood devices and measured the cfm coming out of each duct. After the 4 ton upgrade, the numbers under the 4 ton for ac were being met. The measurements under the 3 ton, we're not.

Did I say that right?
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Old 06-06-2013, 05:03 PM   #15
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Thanks, they used one of those fancy hood devices and measured the cfm coming out of each duct. After the 4 ton upgrade, the numbers under the 4 ton for ac were being met. The measurements under the 3 ton, we're not.

Did I say that right?
No, its confusing.

But it may mean that the 4 ton air handler has a VS blower that is over coming the under sized duct work problem. And the 3 ton air handler had a standard blower, that could over come the under sized duct work.

Which would mean the problem was the duct work, and not the A/C size. So if you had them fix the duct work instead of just putting in a larger A/C. You would have good cooling and lower cooling bills.


PS: A hood can easily be off by 10% or more.

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