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Installing an AC System
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K
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23 Jul ’16 - 8:40 pm
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I think ours was 7000 but that was 9 years ago

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icanreachit
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25 Jul ’16 - 11:41 pm
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I just thought it was high after having another fellow quote 6k and this guy saying he didn't even plan to pull permits. Figured it's time that I learned how to do it.

So I sat down today and ran the Manual J calculation based on my window sizes and knowledge of the building. Ended up around 22,000BTU for cooling needs and the same for heating. This supported the 2-ton need and I think I'm going with this unit. Slightly more expensive but it has a variable speed fan which I think should be more efficient and leave the system with a longer life:

 

I then started designing the duct work. I'm not sure if I'm overthinking this but it seemed worthwhile considering my lack of experience. 

I've decided to take a basic square footage estimate instead of using the manual J for each room. I was able to size the system to a 2 ton unit using the Manual J and keeping in mind a desire to build out the car port at some point (an addition of 200sf or so).
 
  SQF CFM Duct Reqd    
System 860 910 18x10    
Room 1 140 148 8    
Room 2 140 148 8    
Room 3 140 148 8    
Bathroom 40 42 6    
Kitchen 240 254 10 Trunk Line 12
Living 160 169 10
I'll use an 18x10 duct coming out of the system, tap the bedrooms and bathroom off of the duct with flexible ducting, and then reduce it to a 12" rigid line. The 12" rigid line seems like it should then be enough to provide air for the kitchen and living room. I'd like to do a 14" for this line so that I can tap off of the end for the eventual addition but we'll see what the costs look like.
 
I'm basing all of the duct flows off of the estimates in the chart found below:
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K
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26 Jul ’16 - 9:28 am
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I will print this out and run it by my neighbor, he does hvac

The following users say thank you to K for this useful post:

icanreachit
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icanreachit
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1 Aug ’16 - 10:27 pm
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Now that I know the dimensions I'm slowly designing the ducting. I know that it's not as critical as I'm making it but I'm trying to design with the following in mind:

  • Unit comes pre-charged for 15' of refrigerant line
  • Keep the return air register in a public area (no bedrooms)
  • Maintain access to unit for maintenance of condensate line
  • Put supply registers as close to the outer walls as possible (ultimately determined by roof pitch, 3:12)

The first run was very obviously a fail. Main trunk will be fiberglass duct board. 

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K
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3 Aug ’16 - 10:43 am
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I love the sketches you make for your projects

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icanreachit
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3 Aug ’16 - 11:24 pm
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It helps me to visualize what I'm planning, that way when I get to building I don't need to slow down. 

Came up with Layout B that seems more straightforward (less static pressure) but it requires slightly more ducting. It also complies with the four requirements that I mentioned earlier which makes it ideal. I'll just have to come up with a way to put in an attic door that's secure/lockable.

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K
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4 Aug ’16 - 9:38 am
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Is that the new house?

Haven't seen my neighbor the past week since he has been on call, he starts vacation tomorrow so I should be able to hit him up this weekend.

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icanreachit
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4 Aug ’16 - 1:28 pm
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I wish! The new house was built in 1961 so it's not quite as nice. Trying to get my wife to pick a paint color at the moment. I was just looking for inspiration for the attic access door. It will be a lot easier to do what you mentioned previously: cut an access hole, load the equipment through there, and then close it back up. 

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