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  1. #1
    Join Date
    Dec 2013
    Posts
    21

    Pro's: check out my home's ducting...

    Hey All,

    About a month ago, I did my own Manual J (with assistance from the pros here) to give myself an idea of a properly sized heat pump for my home. After posting my calculations for my 1412 sq ft house in the Portland, OR metro area, the consensus was 2 ton heat pump.

    I just spent a decent amount of time looking at the ducting in my attic. This was a huge chore because I have vaulted ceilings in the house, thus, there is only about a 3-4 foot tall "attic" to crawl around in. I pretty carefully researched all my ducting, noting the sizes of everything. I diagrammed my findings below in a "to scale" drawing of my home. Basically, all I have is flex ducting and the widths range from 5" to 8" for hot side, and a 14" width for the return (20x20 filter).

    I'm going to have a heat pump with electric backup installed, and a leak test will be performed before hand to make sure the house ducting is sealed properly.

    **My question to you guys: I intend to stay in this house for about 4 more years. I don't want to change the ducting if I don't have to because that would be a huge additional cost. I feel like the air at the farther end of the ducting system should come out with more force than it is with my current hardware. Can anybody look at my findings and tell me what range of CFM for my air handler I'd be looking at?**

    Here is a photo of the return supply:
    https://scontent-a-sea.xx.fbcdn.net/...64684734_n.jpg

    Here is a panorama of me sitting on my air handler and looking down the long end of my "attic" (note that my ducting is virtually all covered by cellulose):
    https://scontent-a-sea.xx.fbcdn.net/...68144604_n.jpg

    Below is a diagram with measurements of my flex ducting and appropriate widths

    Thank you for your time.
    Attached Images Attached Images  

  2. #2
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,057
    If it were me... I would get an HVAC guy out to look over your numbers. Ask them on the phone if they do load calc's and explain what you want.

    Do not be surprised if you have to call a lot of folks to find someone who will help.

    Let us know what you find.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  3. #3
    Join Date
    Dec 2013
    Posts
    21
    I taken it they'll have to do manual D (mocking my current setup) in order to do manual S right?

    And of course im sure they'll do their own manual J.

  4. #4
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,652
    You have approximately 800 cfm on both the supply and the RA (return air). The blower will probably be capable of moving up to 1,200 cfm. I would try to size the ductwork for 1,000 cfm to make it more efficient and quiet.
    Note: The 2 ton needs 800 cfm.
    Last edited by George2; 01-30-2014 at 08:58 PM. Reason: note added

  5. #5
    Join Date
    Dec 2013
    Posts
    21
    Quote Originally Posted by George2 View Post
    You have approximately 800 cfm on both the supply and the RA (return air). The blower will probably be capable of moving up to 1,200 cfm. I would try to size the ductwork for 1,000 cfm to make it more efficient and quiet.
    Note: The 2 ton needs 800 cfm.
    george2 - thanks for your reply.

    pretty much the only ducting i think anyone will be able to modify is the return air duct. the reason i say this: since i have vaulted ceilings, there is VERY little crawl room. I am a 5-7 145 athletic guy and it was a huge PITA to crawl around up there (there is like 4 feet vertical clearance). the ceiling registers are at the outsides of the house where there is probably 1 foot of vertical clearance... no idea how anybody could reach that now. which is why i would rather not touch the ducting. the ducting is also submerged below cellulose in most areas.

    what would happen if the return was increased from 14" to 16", but the rest of the ducting left alone? would i start blowing up flex piping?

  6. #6
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,057
    If we are gonna give advice... which we really are not supposed to... here is what I would do:

    Change that 8" trunk to 9" (not 10"), upsize the return to 16", and mount a 20x25 filter.

    And this is the IMPORTANT part: Variable Speed drive for the air handler!

    Do this, and you will have relatively even air distribution. Note I did not say your calculation of 2 tons is correct. I would NEVER attempt a LC without visually seeing the property.

    Now here is one more thing to consider: If you did all your 'estimated' items in the load calc correctly... then you will have adequate capacity. If you did not (and do not realize it), you could be off. Either too large or too small, will cause issues.

    Knowing how to do the 'variables' is what one pays a professional for...
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,652
    Is the AH (air handler) in the closet or the attic? If there is room (easy access) to the plenum, just add another 8" blowing into the "hallway" to give some relief on the supply side. Do as G-H-T said on the RA side and you should have a quiet system. The VS (variable-speed) blower is really "sweet" but if money is an issue, at least get a X13 motor (cheap efficiency).

  8. #8
    Join Date
    Dec 2013
    Posts
    21
    Quote Originally Posted by ga-hvac-tech View Post
    If we are gonna give advice... which we really are not supposed to... here is what I would do:
    GHT: This isn't a DIY thing, I just like to ask a large audience for clarification during project planning, just so i can be more informed i do appreciate your suggestion. between you and Geroge2, i have a better understanding of what's going on and some ideas on how a professional can remedy the situation!

    Thanks to you both. If anybody else has any ideas please feel free to share. I will probably also make a thread when i get a few quotes / people out to the house, just to see what people think here

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Your 14" flex return is small for 2 tons. So is your 20X20 return air filter grille. Your supply is small for2 tons also. Both your supply and return duct system is more appropriate for 1.5 tons.
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  10. #10
    Join Date
    Dec 2013
    Posts
    21
    Beenthere -

    Currently I have a 2 ton AC. not sure about the air handler.

    I'm not at the house to provide exact #s, but per my own manual J my cooling requirement is around 13,000 and my heat is around 23,000. I could probably get away with a 1.5 ton (assuming my #s are correct). I thought a 2 ton 2 stage would be better though. Thoughts?

  11. #11
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    21,057
    IMO 2 stage is always better... not everyone wants to spend the $$$ up front though...

    The reason 2 stage is better... is more in AC: It matches the load to the run time... which is important for de-humidification.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  12. #12
    Join Date
    Dec 2013
    Posts
    21
    i'm pretty ignorant on the dehumidification topic - however, being in the PNW that's not really an issue here.

    for that reason, i think an X-13 air handler would do fine.

    we'll see what local guys have to offer when i start getting some quotes.

  13. #13
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    1,977
    If you have not already called us at Sky Heating please give us a call to look at your options. We will perform our own Manual J calculation on the house and are PTCS certified for blower door ductwork testing.

    Your setup is pretty typical for this area and I would not spend the extra to redo the ductwork for your short timeframe. I have no doubt that a 2 ton is the right size just buy guesstimating the home since Portland has very little load(although this last week has been a bit odd!)

    My name is Travis, let me know if there is anything I can do to help locally.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
    Like us on FACEBOOK if you like our advice here!

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