Are these returns adequate? (pictures)
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  1. #1

    Are these returns adequate? (pictures)

    We have a new 5-ton dual-fuel heat pump with gas aux. We have been fighting balancing problems, as some rooms are up to 8 degrees cooler than others. Also, the total fuel usage (both electricity and gas) of the system is higher than expected. I am worried that there is something that is keeping the system from operating at (or even near) its peak efficiency.

    One thing I am worried about is the returns. There are two 12-inch ducts, one at each end of the house, with 20x25 inch filters. Is this adequate for a 5-ton system?

    The first duct comes up through the floor into a huge metal box that takes up a large amount of room in one of the bedroom closets. The installer told me that because of the position of the floor joists he had no other choice. There is a 9 3/4" x 20" hole cut into the floor (see attached pictures). This looks very restrictive to me.

    The return is open to the interior wall and floor. I am wondering if the amount of unconditioned air being drawn in from the attic and crawlspace could be a problem. I do not see any evidence of sealing compounds used where the sheet metal and wood join. Does leakage in the return matter? I realize the whole house is leaky...

    Thanks
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  2. #2
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    Return

    For a 5 ton unit with 2 returns, 12 inch is not large enough. On a .1 that is only 700 cfm per pipe. I would suggest at least a 14 inch pipe with a 24x24 filter for each. As far as the opening in the floor, it depends if it is lined inside or not. Without liner it is just large enough. If it is not feasable to enlarge the filter area, I suggest pleated filters.

  3. #3
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    May or may not be drawing attic air down that cavity. It should have been blocked and sealed.
    The 2-12" returns are not nearly enough. Your starved for return.
    2-16" maybe, but not 12 inchers.
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  4. #4
    Quote Originally Posted by red73 View Post
    For a 5 ton unit with 2 returns, 12 inch is not large enough. On a .1 that is only 700 cfm per pipe. I would suggest at least a 14 inch pipe with a 24x24 filter for each. As far as the opening in the floor, it depends if it is lined inside or not. Without liner it is just large enough. If it is not feasable to enlarge the filter area, I suggest pleated filters.
    What is a liner? The hole doesn't appear to be lined with anything as far as I can tell. It's just the bare wood (with a joist going right through the center). See return_1_b.jpg.

  5. #5
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    Insulation inside the return air plenum (box). I could not pull up the pictures.

  6. #6
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    Like beenthere said, you don't have enough return air, unless there's more down at the heater coming from another area. What are the totals at the heater? What are your supply and return air temperatures, both at the heater and at the grills and registers?

    Go online and get an air duct calculator. To get specific, you'll need to know variables, but they can give you a rough idea. Here's one from Hart & Cooley.
    http://www.hartandcooley.com/flex/Ai...Calculator.xls

    Make sure you aren't using pleated "high efficiency" filters, which will severely restrict your air flow.

  7. #7

    Some naive questions about RETURNS

    I hope this is not too naive a query, but I'm an Owner in a Condo Association, where we have Trane Heat pumps working in our units, which are Duplex, 1200 sq feet, with 2 BRs and a duplex cathedral ceiling in the LR. There is only one return in the units downstairs in a closet in the LR. Is it possible that many of us feel insufficient ventilation....as well as either heat or cold...in our upstairs BR [no return] and our downstairs BR [also no return]. We've been told to keep the doors open at all times, but this doesn't always work. Some folks, especially seniors and infants have been complaining of headaches, asthma, breathing difficulties, etc.

    How do we start remedying this? Do we get someone in to test our ventilation? Do we go about possibly seeing if we can install additional returns in the bedrooms where people are complaining? Any help would be appreciated.

  8. #8
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    You need a contractor to come ouot an investigate your systems.
    You may have other troubles besides lack of return.
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  9. #9
    Quote Originally Posted by bobb25 View Post
    Like beenthere said, you don't have enough return air, unless there's more down at the heater coming from another area. What are the totals at the heater? What are your supply and return air temperatures, both at the heater and at the grills and registers?

    Go online and get an air duct calculator. To get specific, you'll need to know variables, but they can give you a rough idea. Here's one from Hart & Cooley.
    http://www.hartandcooley.com/flex/Ai...Calculator.xls

    Make sure you aren't using pleated "high efficiency" filters, which will severely restrict your air flow.
    Those are the only two returns in the system.

    By totals, do you mean air flow in CFM? I don't know that number; I'm trying to see if the installer has measured this. I don't have the equipment or knowhow to do it.

    I can measure the temperatures at the registers and return grill; not sure how to measure at the furnace.

    Ok, now I am confused about filters. red73 suggested pleated filters, but you say to avoid them. I am using pleated filters, 20x25", of the 3M Filtrete type. Should I avoid these? What do you recommend? I thought I was doing the right thing by getting 'quality' filters.

    Thanks

  10. #10
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    Quote Originally Posted by castalia View Post
    I hope this is not too naive a query, but I'm an Owner in a Condo Association, where we have Trane Heat pumps working in our units, which are Duplex, 1200 sq feet, with 2 BRs and a duplex cathedral ceiling in the LR. There is only one return in the units downstairs in a closet in the LR. Is it possible that many of us feel insufficient ventilation....as well as either heat or cold...in our upstairs BR [no return] and our downstairs BR [also no return]. We've been told to keep the doors open at all times, but this doesn't always work. Some folks, especially seniors and infants have been complaining of headaches, asthma, breathing difficulties, etc.

    How do we start remedying this? Do we get someone in to test our ventilation? Do we go about possibly seeing if we can install additional returns in the bedrooms where people are complaining? Any help would be appreciated.
    IMO, calling HVAC contractors for their opinions right off the bat will give you several different opinions about what to do. Some of them will have great ideas, but some just be trying to sell you something.

    The first thing you need to do is get an engineer in to check the system design, assuming all sytems are alike. You'll probably have to pay them, so interview them just like you would any other professional. Find out what their credentials, how much they charge, and what exactly they'll do for the money. In other words, are they going to design needed modifications, with measurements, or are they just going to tell you to add x number of cfm or what. It's best to get some kind of written details.

    After that, call HVAC contractors and show them the specs and get price quotes.

  11. #11
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    Like already said two 12 inch ducts are not big enough and to make matters worse just by looking at that last picture I can tell you aren't even getting a full 12 inches.

  12. #12
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    Quote Originally Posted by CaptainKangaroo View Post
    Those are the only two returns in the system.

    By totals, do you mean air flow in CFM? I don't know that number; I'm trying to see if the installer has measured this. I don't have the equipment or knowhow to do it.

    I can measure the temperatures at the registers and return grill; not sure how to measure at the furnace.

    Ok, now I am confused about filters. red73 suggested pleated filters, but you say to avoid them. I am using pleated filters, 20x25", of the 3M Filtrete type. Should I avoid these? What do you recommend? I thought I was doing the right thing by getting 'quality' filters.

    Thanks
    I've solved many problems for customers by telling them to get rid of those pleated filters. Does your system work ok with El Chepo brand filters? If you don't have any, how does it work without any filters?

    You really need to get an HVAC contractor, and not the guy who installed it.

  13. #13
    Quote Originally Posted by trane View Post
    Like already said two 12 inch ducts are not big enough and to make matters worse just by looking at that last picture I can tell you aren't even getting a full 12 inches.
    I think I am beginning to put the pieces of the puzzle together. I now feel sure that we have undersized returns and room pressurization issues (no returns or jumper ducts in bedrooms).

    I suspect there are other problems, such as leaky ducts where the new flex duct connects with the old boots.

    Getting this system to live up to its potential is going to take some work.

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