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  1. #1
    Join Date
    Sep 2007
    Location
    Sarasota/Bradenton, FL
    Posts
    56

    How to solve two problems...

    So, I have a home built about 1980. All prior owners appear to have been very conscientious in terms of maintenance. So, without specifying the "R" value, the attic insulation appears to be new, within the past 5-8 years. Windows are Pella, but circa 1985.

    All my problems regarding this post relate to one area. It is an area of approximately 1000 sq/ft, with 8.5' ceilings. About 500 sq/ft of this is a master bedroom/bath, and it communicates -- in terms of hvac -- with the main area of the house. It contains a bathroom (with a large shower, tub, two sinks, toilet, & bidet).

    The area described above is conditioned by 2.5 ton unit.

    This 2.5 ton unit is somewhat oversized. I could do the calcs, but I'm mostly basing this on comfort. The area is cold -- and clammy. That is, the temp drops very quickly, but the drop in humidity lags.

    The rest of the house (about 2500 sq/ft, 4 ton unit) is ok in terms of humidity and temperature.

    My problems are as follows:

    1) Closet.

    It appears that someone moved a wall, and created a long, narrow, 'walk-in' closet out of one end of the master bedroom. The problem is that, there is only one a/c vent, at the entrance, and there is no circulation of air in the closet. That is, air does not flow the length of of closet, from one end to the other.

    2) Bathroom.

    Well, this is mostly a large shower, it is used daily, and it is never dry. Mold, etc, are the typical problems.

    So, I am wondering about the following solutions...

    1) I install an 80cfm bathroom fan in the closet. It will run continuously. So, it is ventilating an area of about 206sq/ft -- all the time. I am sucking air mainly from the 2.5 ton unit, from the bedroom/hall(4 ton unit), and simply circulating air.

    The bigger question is should I:

    a) just dump the closet air up and out into the attic...and the outside...essentially reducing the tonnage of the a/c unit...or....

    Perhaps I should:

    b) dump the air back into the master bedroom, via a vent. (Or basically a hole in the wall -- a very easy solution.)
    c) install an actual return back to the unit. (the attic is very open and accessible; so, this, and the prior, solutions, would be very easy to do.) So, I simply add a return to the far end of the closet, and keep the present (close end) vent. This gives me circulation -- b ut onlywhen the a/c is running, not otherwise -- and dehumid, again based on a/c efficiency.

    Personally, I like the idea of the continuously running 80cfm low level fan -- continuous ventilation is good -- but I'm really not sure where I should dump the air...? Out or in????

    Bathroom. Humid as hell.

    2) My plan is to install a 350cfm in-line fan to vent the shower. It will run a max of 25-30min after use or shower. So, the question is, given what I am asking above, if I remove these 300cfm's of air from this area daily, am I...

    ...well, screwing up the current 2.5 ton a/c?

    Tips?

    Thoughts?

    Thanks!!

    b

  2. #2
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Definitely vent the bathroom. Vent it to the outside. Install a timer switch so you can control how long it's left one. That's a absolute must. The inline fan with multiple pick-up points is a good solution for a large master bath. You want that moisture out of your home summer or winter. It's too much moisture, uncontrolled and in too small of a space.

  3. #3
    Join Date
    Sep 2007
    Location
    Sarasota/Bradenton, FL
    Posts
    56

    Where to dump the air??

    So, this is a follow-up to my original post.

    Two questions:

    1)

    I've decided to go with a variable speed continuous ventilation solution for the bathroom.

    High CFMs for when the shower is actually used.

    And very low continuous CFMs when the shower is NOT being used -- just to keep the humidity under control.

    The question here is, how do I determine the best low, continuous, CFM rate for the bathroom?

    The idea is to just keep the moisture evaporating from sinks, toilets, etc. -- when not in use -- mostly out of the space, and outside.

    The A/C involved is a 2.5 ton unit cooling about 1000-1200 sq/ft and, given the perceived moisture/comfort level, is about 1/2-ton too big. So, it can handle, I would think, some air being dumped outside. (I'm aware of negative pressure issues, but exterior doors/windows are open and shut so often in this house, that I do not think this is a consideration.)


    2)

    In the same space, I'm continuously venting the long/narrow closet of about 200 sq/ft. I'm using a 57 CFM fan, and I just need maybe 1 or 2 air exchanges/hr. There are no moisture issues here, just stagnant air.

    Where should I send that air?

    Back into the space cooled by the 2.5 ton unit?
    Into the main part of the house -- much larger, and cooled by a 4 ton unit?
    Or outside?

    Any advice will be much appreciated!!

    Thanks!

  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    IF you venting a bathroom, you want the humid air out out of the house.

    The size of the fan on high should be determined by the size of the bathroom and number of showers and tubs in there. Sicne it runs on-demand, theres no harm in oversizing it a little.

    If it's a sizeable master bath, I'd go with 100CFM, larger if it has a larger heated whirlpool tub.

  5. #5
    Join Date
    Sep 2007
    Location
    Sarasota/Bradenton, FL
    Posts
    56
    Well, for the "high" setting, I figure the CFMs at about 200. Like you say, the "high" setting only runs for 20-30min. So, even if it's too much, so to speak, it should be a problem.

    But the product I'm using is a continuous ventilation fan.

    So, it will always run at some slow speed. That's what I'm trying to figure out -- the best slow, continuous, speed.

    Thanks!

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