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Old 06-07-2009, 08:02 PM   #1
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Trane XR12 1.5 ton-Too small for my house?


We are entering the second summer in our house and I'm starting to wonder if our AC unit is undersized. Usually we try to not let the house get too warm in the first place by keeping the shades down and turning the air conditioning on in the late morning when the house is about 70 degrees. In order to keep the house at 70 though the unit seems to run continuously. Recently we had a family gathering and with lots of people in the house we couldn't get the temperature down from 74.

As stated in the title the unit is a Trane XR12 (build date 1/2003) 1.5 ton as verified by dividing the 7th and 8th digits of the model number (18) by 12. The house is a simple rectangular ranch, about 1100 square feet with 8 foot ceilings, 2x4 walls with fiberglass insulation (no idea on the R-rating), 6" of fiberglass insulation in the ceilings, fairly new vinyl windows, one picture window with a wooden frame that's a bit drafty, and three exterior doors that are a bit drafty. The house was built in the mid-60s with forced air oil heat so the AC uses the existing ductwork. The coil sits at one end of the house and feeds into the trunkline which runs the length of the house (about 45 feet) with 6" delivery ducts branching off. We have attic fans but ventilating the roof doesn't seem to help. To address the obvious we change the filter religiously every 30 days due to allergies. Finally, the rear of the house faces directly south. There are only 3 south facing windows, but we don't have any shade so the rear roof (simple a-frame) and rear wall get a lot of sun. So, given all of that, does it sound like my unit is undersized? If so, how much will it help to tighten up the house, add insulation, etc...?

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Old 06-07-2009, 08:32 PM   #2
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Trane XR12 1.5 ton-Too small for my house?


I would guess that the a/c unit is not keeping up with the heat gain. You will probably want to put money into insulation as it will benefit you greatly in the heating season as well as cooling. It is not uncommon to have 30+ inches of fiberglass in the attic. Six inch insulation is generally what you would use in exterior walls. Adding insulation and tightening your house up will probably cure your cooling issues. 1.5 tons should be adequate to cool that size of a house. You may also have a refrigerant charge that is adequate which will need to be checked by a competent tech..

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Old 06-07-2009, 10:58 PM   #3
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Trane XR12 1.5 ton-Too small for my house?


I'm wondering if you live in the hot south like me. I just replaced AC's at my house and had done a lot of research on this subject. The Trane might be a variable speed model. Have someone hopefully honest to check dip switches, pressure check, duct seals, vents, whatever you can think of! And these new thermostates can be trickey too. If all that checks out, insulate insulate, insulate. Try a radiant barrier. The foil not the spray. And make sure your attic is vented. When it's in the upper 90's to 100 you can only hope to be around 76 inside probably.
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Old 06-08-2009, 12:08 AM   #4
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Trane XR12 1.5 ton-Too small for my house?


one thing I found that help me was I had single glass window I put new window in with 2 glass and the gas in them or you can use storm window they will help some I have used them before

replace the rubber around the doors and under the doors it is a cheap fix

with the fan in the attic make sure that it is getting air from out side or it will pull the cold air from in the house and make your a/c work harder
I put a vent on the other end of my house to make sure that air flow was good

one last thing I did that helped is plant a tree on the south side of your home it will take some time to help but in time it will
best of luck
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Old 06-08-2009, 07:32 AM   #5
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Trane XR12 1.5 ton-Too small for my house?


From the limited information you have given it is impossible to tell if that unit can handle your house, but given your homes age and other things you said it could be a little small. But that is simply a wag. The best way to model your heat gain is with a Manual J using a program such as HVAC-CALC. For the price you can model your heat gain given your locale and other factors. I would also have a pro come in and verify your system is running at peak efficiency. Be sure they check the delta T across your indoor coil.

Let us know what you find and we can make some recommendations from there.
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Old 09-22-2009, 10:39 PM   #6
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Trane XR12 1.5 ton-Too small for my house?


I had the same problem this summer. When I had a tech come and check my unit out he found a small crack in the coil in the XR12 unit itself. He said that the vibration of the XR12 caused the coil to vibrate and rub on a grommet that that wore down. That wear has caused a small leak of coolant.

Apparently my XR12 is still under warranty and the part will be free from Trane. However, I have to pay a delivery fee of $75.00 and $500 to a technician to install the coil and recharge the coolant.

In the meantime the technician recharged my coolant and that helped to get the house cooler in the hot months.
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Old 09-23-2009, 12:05 AM   #7
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Trane XR12 1.5 ton-Too small for my house?


hey one more thing if you put in a new ac go and buy if your self do not let the ac man get for you let him tell you what you need and go get it your self save about 3 to 4 hundred $ you can get it because it has no freon in it but the ac man marks it up to make money pleas no email from the ac man thank you we all trying to get by in this world that is why we are on DIY
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Old 09-23-2009, 05:48 AM   #8
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Trane XR12 1.5 ton-Too small for my house?


A. New A/C units do indeed contain refrigerant.
B. Purchasing an A/C and having a contractor install it for you, is NOT DIY. Its providing your own equipment, and loosing labor warranty(not always a big deal). But that is not the definition of DIY.


As posted earlier. Improve your attic insulation.
If you have powered attic fans. Seal your attic access(access tent), and make sure you have enough vents in the attic. That those fans don't draw air from the house. And cause even more fresh unconditioned air to enter your home.

Sealing your doors, windows, along with receps and switches, will help a lot.

1.5 tons is probably the correct size.

A/Cs are not sized to handle a large gathering of people. That may only occur once in a while.
Depending on activity of those people, you add anywhere from 450 to over 1000 BTUs per person.

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