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  1. #14
    Join Date
    May 2008
    Location
    Bergen County, NJ
    Posts
    36
    I did get pleated 3M filters (model 1700). Questions, what does it mean to cause negative pressure and is there any easy way to tell if its causing it? As for its being isolated from the rest of the house... the only thing dividing the attic from my second floor is one of those pull down staircases and I know the seal around that is not air tight.

    In terms of the smaller than desired return, does one 25" x 18" for 9 open registers sound little to you guys?

  2. #15
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,929
    Its small for your system size.
    Remember, when you start closing off supplies. If your supply duct has leaks, you increase teh amount of air being blown outside of the conditioned space. And can cause more fresh air to be drawn into the house, raising humidity.
    Neg pressure from the attic fan will draw the air from your house into the attic, and cause fresh high humidity air to be drawn into the home.
    Reset your attic fan to 90, and see if it makes it better in your house.
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  3. #16
    Join Date
    May 2008
    Location
    Bergen County, NJ
    Posts
    36
    Great. Thanks for the explaination on the negative pressure thing. I thought I was helping out my system by cooling the area it was installed in but now I see I could have been doing myself a disservice. I'll set that fan back up to90 degrees to see what happens.

    As for the return... I'm having my HVAC guy come back out on Thursday to install some dampers in my 6" flex pipe and to check if my upstairs unit has a leak because I lost a pound of frion within 14 - 20 days. While he's out I'll ask him to make the return a larger size.

    BTW - You guys had suggested that I make the blower speed lower to help with the humidity problem but when I passed this info to the HVAC guy he said he wasn't aware that the speed of a blower can be modified unless it was a variable speed. Is the blower speed something that can be modified for all units?

    Thanks!

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,929
    New air handlers have multispeed blowers, Either 3 or 4 speed. (low, med low, med high, high) He should be able to set it to a lower speed.
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  5. #18
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Is everybody going to be OK with 3M filters on this thread? They have been discussed so many times before on this forum I expected an immediate reaction.

    Speaking as a homeowner I would ask your AC pro about whether a generously large filter and return could be put on your system.

    Regards -- Pstu

  6. #19
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,929
    Bigjon, already told him the pleated can restrict air flow. That jon guy is on top of things.

    But yes, 3M makes just about the most restrictive.
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  7. #20
    Join Date
    May 2008
    Location
    Bergen County, NJ
    Posts
    36
    Can anyone recommend a good disposable filter?

    As for the blower speed. I told my new installer about the multiple speeds and he told me that he doesn't want to lower the speed because cool air is heavier than hot so it will be harder for the system to push the air. You guys on this forum have done me right in the past so I'm starting to question my new guys comments.

  8. #21
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,929
    The general pleated filters are usually ok. Those are the ones that the pleats are rounded curves, not sharp angles.

    Although 130 CF of 50* air is heavier then 130 CF of 52 degree air.(a tenth of a pound or so)
    Lowering to the next lower fan speed should not drop off air flow enough to make any rooms lack air flow.

    Its no different then setting a VS blower to a lower CFM.
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  9. #22
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Quote Originally Posted by CoquiLostInNY View Post
    Some more questions regarding high humidity levels.

    I was recently told by my new HVAC guy that the original installer never installed filters in either of my units (he actually left the construction filter in) so I went out and purchased some disposable 3M three month filters which I installed. In addition I set the small fan in my attic to automatically turn on when the temp reaches 75 instead of 90 like previously set.

    After installing the filter and turning on the attic fan I noticed the humidity in my second level jumped to 62 percent during the night time hours but during the day the level dropped down to 49 - 52 percent. Could installing the filter or turning on the attic fan made my humidity problem worst?

    Also, while at Home Depot picking up the filters I started talking to the sales guy and explained my situation. He said if my return register was too small (its only 25" X 18") that my system could be straining to suck in the humid air. Is this true? If so, how large should I make my return if I have a total of 14 supply registers, 9 which I constantly leave open.

    Thanks.
    Your return is 25 by 18, which is 450 sqin of filter area (did you ever say the size of duct behind it?). And your AC is 2 tons. Are these correct statements for your house? Is there any other evidence your return is restrictive?

    Thanks -- Pstu

  10. #23
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741
    if your "new" guy does not know about matching blower speed to the outdoor unit and ductwork it may be time for a "new new" guy........

  11. #24
    Join Date
    May 2008
    Location
    Bergen County, NJ
    Posts
    36

    Post

    Pstu,

    You're correct. The Weatherking model servicing my upstairs level is a 2 ton unit and I only have 1 return grill which is about 25" x 18".

    As for evidence the unit is be restricted.... I'm going by a couple of people tellign me that one 25" x 18" return for an area that has 14 supply registers (which 9 are always open because of that high / low registers configuration) is small. In addition I don't feel a great amount of air coming out of the supply registers when the unit is on.

    Something else that came to my mind while reading various post on this site is that since I never had a true filter installed in this unit that there's a good chance my indoor coil could be dirty. Would you guys agree? Would it be easy for an HVAC pro to see it the coil needs to be cleaned?

    Thanks!

  12. #25
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,929
    Its relatively easy to determine if the coil is dirty or not.
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  13. #26
    Join Date
    Jun 2008
    Posts
    63
    Quote Originally Posted by beenthere View Post
    Its relatively easy to determine if the coil is dirty or not.
    OK I'll bite. How? Hopefully not by looking at it because I can only see the side edges of mine. And if it is dirty, how would you clean it if you can't see it? I've been thinking of cutting a hole in the plenum to gain access. Good idea or creating a bigger problem?

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