central air not done right upstairs

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Old 06-10-11, 11:07 PM
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central air not done right upstairs

my wife and i bought this house two years ago. the central a/c was put in i think by sears. it's about 15 years old and still works great. however, the upstairs sucks!! when they put it in they put the return and vent on the same wall, the wall closest to the attic which is where the unit is. Obviously they didn't even want to try to get the vent on the opposite side of the room which can only be done through ducting through the floor via the same attic space the unit is installed. My guess is it was probly the middle of August and those guys just wanted to get in and out. the air up in those 2 bedrooms just does not circulate like i feel it should, even the guy that serviced it today asked me who in the world put the unit in. So, i would like to "finish" the job correctly but not sure if it would help. Currently, there are 7" flex ducting hooked to the vents. I would like to simply unhook them, run 7 inch flex under the floor through the rafters to the other side of the room and install a register on the opposite side of the room in the floor. It's about a 12-15 ft stretch from the wall where the register is now and wonder how it will affect the air pressure for the way things are currently set up. Would going with 7 or 6 inch oval ducting help by reducing air pressure? I'm almost certain doing SOMETHING would improve the temp up there. Can't get it much cooler than 78-80 and i don't think the system is getting all the hot air out because all it does is just loop around with cold air vent being on the same wall as the return vent and only about 8 ft apart. People tell me to just put window units in and problem solved. Seems ridiculous to run central and window units not to mention my electric bill. Any one have thoughts or suggestions PLEASE respond. the house was built in 1955 and in great shape but i hope the morans that put this system in were fired or quit!!!
 
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Old 06-11-11, 06:11 AM
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First flex duct should never be run between floors use hard pipe. 2nd do a heat load so you will know exactly how much air you need.
 
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Old 06-11-11, 08:02 AM
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It should be OK if the vent blow air to one end of the room, and the return is at the other end of the room. this will form a circular air motion. 8 feet apart is more than enough. If you can not get the room temp down, may be you have other problems. Upstair is always hard to cool anyway. check you temp drop, insulation(most 1955 house don't have good insulation), cold air blow strong or not, etc. first, before you worry about the location of the vents...
 
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Old 06-11-11, 11:06 PM
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i think part of the problem as well is that the ac unit is in the attic. it gets so hot in there that its hard to breathe. you are correct, the house is not insulated well but the downstairs gets nice. Air blows fairly strong. Temp does come down and if the ac wasn't on it would be much worse. I'm not an Hvac person but i'm willing to bet that most of the problem is because the return and the vent are on the same wall and only 6ft max apart. why can't you use flex duct? If i used hard pipe should it still be the same diameter as the current flex duct? The unit was checked for refrigerant and it was fine. I have noticed that condensate is always in the pan always to the drain level, like it never drains but yet i see dripping outside. I put a shop vac on the line coming out and suck out like half a gallon of water. I can not get any more pitch on the condensate line and it's been this way for years i am told by previous owner and the tray has never overflowed or activated kill switch so somehow the water is getting out but not fast enough to drain pan. My service guy said there will always be water in the pan in the summertime and having water in there doesn't hurt or put any humidity back into the cooled air. However, i have read online that having a significant amount of water in the pan can freeze up the coil. When it's really hot, like in the 90's the unit runs non stop, air doesn't feel that cold, and lots of water in condensate line. After the sun goes down the unit acts fine and i can get temp down to 68-69F. Only option is a condensate pump but i'm not doing that if having water in pan is ok. I don't even sleep in the upstairs bedrooms but my one and a half year old does and so does my other 2 month old. I feel bad when i'm laying in our downstairs bedroom in nice cool room and they are up there in like 78F temp.
 
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Old 06-11-11, 11:09 PM
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I don't know what a heat load is, please tell me about it.
 
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Old 06-11-11, 11:37 PM
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First, if they installed your system the right way, you should never see water in drip pan, in fact, you should not see water anywhere. the water should be drained from a primary drain pipe to your plumbing system, drip pan is for emergency purpose only when the primary drain is clogged. If they installed right, you should have 3 PVC pipes (one primary, one secondary, one drip pan drain) When you see water drip from top of you window, that is a warning sign to tell you something is wrong.
Tell you the truth, all my rooms have vent and return located at the ceiling about 5 to 10 feet apart. It blows the cold air down to one side of the room and circulate back from the other end, I never had any problem. remember, upstair are always hard to cool simply because hot air rises. So, in addition to good insulation, you need at least 18 degree temperaute drop between upstair's vent and return. if not, your upstair are always hot. by moving the vent will not help you. (one more point, at least 80% houses in Texas have A/C in the attic, so that is not your problem)
 
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Old 06-11-11, 11:43 PM
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heat load is a way to measure how much (what size) air conditioning do you need for the house. it counts a lot of the factors, like size of the house, face west or east, how much insulation, how many doors, windows, etc.. there is a special form (called manual J) for that purpose, you can go on internet and search for it.
 
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Old 06-12-11, 06:50 AM
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I can guarantee that modifying your return duct will not help your problem.
Duct location will only help if you are relocating properly sized ducting.
It is quite common for sheet metal installers to be good at installing tin (or in your case flex), but not so good at system design and airflo distribution.

If your system is working as well as it can then a heat gain calculation as mentioned is the only way to know what to do to fix your problem.
IOW it is how much air is getting to the second floor not where the ducts are placed that is causing your problem.

One other thing you need to watch for is that if you were to modify the ductwork to increase airflow to the second story there is the possibility that your ac might not have enough capacity to work properly.
This is why taking a step back and having your house cooling loads re-assed important.
 
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Old 06-13-11, 04:16 PM
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Try a gable fan.... Removing the oppressive 140 degree ambient air from the attic will improve efficiency. Your air handler and ductwork are sitting in that heat, and if its 15 years old, I'd question how well it has held up with the heat-cool cycles.
Flowmaster makes a 1600 CFM gable unit that runs 3.3 amps, 120V and is on a thermostat control. About 100 bucks at Home Depot.
If you don't have a gable then you'll need a roof vent... (more work)
I'm in the process of installing one now. I had a 2.5 ton Carrier unit installed in my attic in November, and now that its June discovered the airflow temps in the morning are 58 and by 2pm, wont blow any colder than 67. The temps in my attic were about 120, and the interior ceilings were radiating heat in the 80's... Check your insulation too.. It will help keep the heat up there, where it belongs.
 
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Old 06-14-11, 10:36 PM
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im going to look into this Gable fan. I can get temps very nice at night time and even into the early morning. but as soon as the sun comes out and beats on the roof the unit loses it's umph!!! whoever installed it used flex duct in the attic. it is insulated, probly R6. wouldn't that keep the heat out? Also, i discovered over the weekend there is no duct work at all! They used the floor space between the second floor and first floor between rafters, made an end cap with insulation, cut a hole in the ceiling and used that as the return to the unit in the attic. Where the flex duct hooked up to this so called "duct" they used 10 inch flex and an elbow and squeezed it down to fit into a 7 inch opening (which is the amount of space between floors) and anywhere it didn't seal they put insulation to close up the gaps. This is sloppy to me and first thoughts are that squeezing down the collar to make it fit into that rafter space would restrict airflow. I bought duct board and made my own end cap that very tightly fit into that rafter space and ran a 10 inch straight take off. the sloppy way the flex hose was more in line with the flow of air but now with my end cap the air kind of now has to go through a 90 degree bend but the collar is not bent at all. Not sure if i increased of decreased air flow. I would only think i would have made it better but it hasn't been hot enough this week for the air to really get a workout. I think if i can get a gable fan up there it will help the temp and the air handler. Like i said, night time it can just get downright cold in this house. Daytime 90's don't feel as good.
 
 

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