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  1. #1
    Join Date
    Dec 2003
    Posts
    23
    I'm building a beach home with 5 bathrooms, each is 5' wide x 9.5' long by 9' high yielding a minum CFM fan requirement of 57 CFM (for 8 changes per hour).

    These showers will likley see heavy use by occupants in the humid summertime. Often there will be 2-3 showers in a row. To avoid excessive build up of humidity, I'd like to size the fan larger than the "minimum".

    Is putting a 110 - 150 CFM rated bathroom fan overkill for this requirement or am I right to oversize the ventilation in this application?

    Thanks!

    bradesp

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    1 cfm per square foot is the minimum around here.

    Consider using a exhaust that can have the grill over the shower,better results than a large increase in cfms.

    Also look at using an ERV/HRV,for the bath exhaust,which will replace the exhausted air ,with"partially conditioned ' fresh air.In this case you would use one ERV (Energy Recovery Ventilator) and duct it to several baths.


    Check out http://www.fantech.net ,for some choices,lots iof brands available ,just a good place to start.



    Another solution;







    Outside showers are fun!LOL!

  3. #3
    Join Date
    Feb 2005
    Posts
    344

    ERV/HRV

    I'm with Dash. Either outdoor showers or energy recovery ventilator for sure.

    Either way you'll greatly decrease the load on the HVAC system.

    To give you an example: If you are in Daytona Beach the 600 cfm exhaust would take about 2.5 tons to temper the make up air. With a ERV the load is reduced to about a half ton and the heating load is reduced from about 29Mbtuh to about 6Mbtu.

    Best regards...

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,268
    Originally posted by dash
    1 cfm per square foot is the minimum around here.

    Consider using a exhaust that can have the grill over the shower,better results than a large increase in cfms.

    Also look at using an ERV/HRV,for the bath exhaust,which will replace the exhausted air ,with"partially conditioned ' fresh air.In this case you would use one ERV (Energy Recovery Ventilator) and duct it to several baths.

    ERVs are designed to transfer moisture from the wet air to the dry air. Operating a ERV reduces the moisture of of the make-up provided the exhaust air is dry. Most transfer 35-45% of the difference. Because of only partial drying, the inside space will be as wet as the outside space after serveral air changes. In this specific case, the wet air being exhausted will humidify the make-up air. Better to use a plain make-up air for this application. A ventilating dehumidifier would resolve all the issues. The most important issue is to remove the moisture left by the make-up air and return the relative humidity to <50%RH within several hours after the showering is finished.

  5. #5
    Join Date
    Feb 2005
    Posts
    344

    ERV/HRV

    TB,

    Right you are. However, we are both assuming the location is in a humid climate.

    I was trying to use a worst case scenario with Daytona Beach. ;-)

    Best regards...




  6. #6
    Join Date
    Dec 2003
    Posts
    23
    FYI, the location is halfway between Wilmington, NC and Myrtle Beach, SC right about 1,000 feet from the ocean. Hot and humid in July/August, but actually quite decent the rest of the year.

    Also, keep in mind this is a rental / investment property. I'm trying to keep things very simple and cost effective. Where I building there is a complete lack of knowledge surrounding "modern methods". So for example, if ERV did prove to be an outstanding way to remediate moisture in this scenario, you'd have a near impossible time finding a contractor in the area who has a clue about how to deal with things like this. No disrespect to the trades there, it's just VERY old school where I'm building.

  7. #7
    Join Date
    Dec 2003
    Posts
    23
    So, back to my original post, is doubling up on the 8 changes per hour a smart idea or dumb idea?

    Thanks.

  8. #8
    Join Date
    Feb 2005
    Posts
    344

    Rental/ Investment

    Why didn't you say so. All that other stuff- never mind.

    Most codes are minimums. Go with what you know.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,760
    Shouldn't be a problem, depending on the doors under cut, you won't get 100 cfm with the 150 fan.



    Teddy, I just put out 2 bids, both including ultra 135's, thanks for your info in other post.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,245

    Thumbs up Large Size

    Originally posted by bradesp
    So, back to my original post, is doubling up on the 8 changes per hour a smart idea or dumb idea?
    Should no tbe a real concern to use 110 CFM fan for
    additional summertime humidity reduction.
    50 CFM more for 10 minutes = 500 CFM total.

    Delta T 92 - 77 = 15'F
    BTUh used = 1.08 * CFM * Delta T
    _________ = 1.08 x 500 x 15 = 8,100 BTUh

    that might cost $0.05
    which would be about 1.7 Ounce of gas
    ...( = nearly a tablespoon) L.O.L.

    1. Who will operate the fans?
    2. Do you actually wish to reduce humidity in the winter?

    3. If they are operated with the light switch,
    the fans should be timed to run ~12 minutes per shower.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Dec 2003
    Posts
    23

    Re: Large Size

    Originally posted by dan sw fl
    Originally posted by bradesp
    So, back to my original post, is doubling up on the 8 changes per hour a smart idea or dumb idea?
    Should no tbe a real concern to use 110 CFM fan for
    additional summertime humidity reduction.
    50 CFM more for 10 minutes = 500 CFM total.
    Dan, Thanks. I have a choice between a 110cfm fan with 4" duct and a 150cfm fan with a 6" duct. AGain, my goal is to clear the hot, humid air from the showers out of the bathrooms as quickly as possible. The beneifit of the 150cfm fan is that it's actualyl as quiet or more so because of the larger duct size.

    Thoughts?

    Thanks.

  12. #12
    Join Date
    Apr 2002
    Location
    Pottsboro TX
    Posts
    181

    Bathroom fan

    Use the bigger exhaust fan. Put it on a timer. Fan will be on usually after shower is over and door will be open to allow full CFM until humidity has been fully removed. Bigger unit wll exhaust extra accumulation from repeated showers before humidity can become a mold issue. I had income properties and did that very thing. Centering fan over shower will help cut down time fan has to run to remove humid air. Positioning of fan over shower is more efficient.
    Phil

  13. #13
    Join Date
    Dec 2003
    Posts
    23
    Phil,

    Thanks! This is exactly the practical advice I was after.

    BTW, do you have a suggestion on the brand/type of timer switch to use?

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