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Upstairs Cooling Problems

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insulation
8K views 36 replies 7 participants last post by  beenthere 
#1 ·
We have a 3200 square foot home and have been having issues since we moved in. First, the house was originally wired up to a 4 ton unit that heated and cooled the whole house. Later, someone added a 3 ton unit for the downstairs. The 3 ton unit uses flex duct in the crawl to heat and cool. This unit blows great and heats and cools quick. The 4 ton unit that use to do the whole house has what I think is flex duct running throughout the house. It is hard/impossible to see this ductwork because of the way it was set up and it doesn't run through the attic upstairs. So we have vents at the ceiling of our downstairs, and vents at the floor of our upstairs that all come from the 4 ton unit setup. I blocked off the ceiling vents downstairs (because the 3 ton unit takes care of downstairs and has registers in the floor.) using magnets and simply closing them. The air coming out of both downstairs unit and upstairs unit is around 60 degrees in the summer. The difference is in the air pressure. Downstairs (3 ton) blows very hard and is awesome. Upstairs the air doesn't blow hard at all in some spots and average in others. I decided to add a return air to the upstairs unit because it was pulling from a small wall cavity and it was like a kink in a hose, the unit wasn't getting enough return air. So I designed a steel box in the attic and connected all of my returns to it, and then did the same where they go into the furnace. This helped very slightly... We also decided to have a company insulate the attic just recently to bring us up to a R45 which is what the region calls for. They used a new fiberwool insulation. Our 4 ton unit used to run all day and still couldn't get the temps down upstairs until 3 in the morning! Now, the temps are lower than they were, but our unit still runs all day trying to keep it at 76 in the summer. I am lost as to what the hell is going on. If it is my ductwork, wouldn't I have to start tearing up the ceiling to access it? And why can't my house cool itself down upstairs? Should I install an attic fan or two up in the attic? I'm just very frustrated with this situation because that 4 ton unit should be able to do the job up there. My 3 ton unit blows so much harder! HELP!
 
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#2 ·
- to fix your problem you need to do load calculation so your system will be balanced for these 2 units
- better insulation and air circulation in the attic.
 
#3 ·
Well we have just added the insulation, so that shouldn't be the issue. We have 18 vents in the attic. But they are just the mesh ones. Do you think I should install some automatic attic fans on t-stats? I think I have a lot of leaking coming from somewhere because it should be blowing a lot harder than it does out of those vents upstairs. How do I get the test that you talked about done? And how much does it cost?
 
#6 ·
If I start talking about things now I'll be assuming. We need numbers to help better.
 
#7 ·
so i need numbers using that calculator progam? I am not very HVAC savy, so I dunno how well I can help you help me haha. It is really weird because my unit looks like it doesn't use flex duct upstairs, but when I got into the attic via closet I saw a flex duct feeding a downstairs ceiling register. But I felt cold air around it as well. I bet it is all messed up but I feel like the only way to get to it is to tear open the dry wall and start fixing it one at a time which will be basically tearing up my entire house!
 
#13 ·
my air blows very very slightly better with the cover of the return blower off. But it isn't a huge difference. It is 81 outside but only 80 upstairs with ac blowing and set at 75. it has been running almost all day. the temp coming out of the vents is 59. I just don't get it... I don't know what is going on. We even added a return duct to the furnace and everything. I put paper up to the returns and it sticks to the vent. It just seems like it is working really hard just to cool it and it can't catch up or something. We just had the attic insulated so I don't know why this is happening. Can anyone else help?
 
#16 ·
I don't know how to run the supply because it is in between the floors. It doesn't appear in the attic except when I look under the floors from a closet. But the duct looks to be like 8 or something. I have a 16" coming into the furnace as a return as well as another box return coming off the furnace.

The only thing that appears in the attic is the returns as they are in the ceiling in the rooms.

What is Delta T?
 
#19 ·
yea but my upstairs won't cool! The air coming out is cold, but doesn't flow out of the register as well as my smaller unit for downstairs...it is weird. And we just had USA Insulation (Website http://www.usainsulationindianapoli...google&matchType=b&c=1294378852&bc=1294378895)
come and bring the R value in the attic to 45. So I am trying to figure out what the hell is wrong with this thing cause our newborn is hot and our unit runs all the time.
 
#20 ·
If your heat load and duct are correct. I think, only zoning will even out the temp differences..
 
#24 · (Edited)
ok i will do that. would me having 4 returns upstairs and only one return downstairs mean anything?

My 4 ton unit has 2 returns hooked into a wall cavity that goes into the attic and into a duct board box that has 3 returns hooked to it (south side room return, hallway return, and master bedroom east side return). The fourth return is in the master bedroom as well but is part of the wall cavity, so I sealed it off so that the air pulls from the attic return setup and not just that return in the master bedroom that I sealed off. My 3 ton (downstairs unit) has a return on the stairway accross from the thermostat.
 
#25 ·
ok i will do that. would me having 4 returns upstairs and only one return downstairs mean anything?

You'd be removing more heat as long as the returns are on the ceiling as heat rises but if you can't put them there then as best possible. You can never have too much return air. You can have 100 returns on one system and you will not affect the performance by having too many. Too little as in restricted and yes, you'll have problems but you've already figured that out.

But the problem is the high static pressure on the supply side. Your air is not moving so either your duct work needs to increase in size to the existing registers or you can add one or two smaller ones elsewhere in problem rooms, granted you have the space on your supply plenum.
 
#26 · (Edited)
I think this could be the only thing left to look into. This is why this is difficult. They ran the ductwork between floors 1 and 2 for the upstairs (because this system used to heat and cool both floors. So there is registers on the downstairs ceiling and on the upstairs floors.) so the only way to get to it, is to tear open the ceilings (or floors) of the house. I know that my 3 ton unit downstairs has wider duct than my 4 ton unit upstairs. I saw one of the ducts when I was in the side portion of the attic to a closet and they seemed small and I felt cool air coming from the cavity that the duct was in...so does this basically mean that my ductwork is ****, I have clogs/holes, and that the only way to fix it is to tear apart the house?

What about Aeroseal? They spray it into the ducts and it seals leaks (If I have them).
 
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