Unique Home Design Details - Bathroom Fan Design with Kitchen Fan Design Supplement

• Before The Architect is amazed at how little attention is given in anybody’s house plan to such an important subject as exhaust fans.
• It's honorable mention at best in most 
  • A cutesy picture of a whirly-gig sort of symbol in a bathroom floor plan or electrical plan.
  • End of story.
• Left to chance
  • Air circulation is inadequate
  • Exhaust could be backdrafted
  • Mechanicals could be needlessly noisy forever and a day

• Fan(s) for bathroom exhaust 
  • Shall be located in each bathroom without regard to that bathroom’s site within the house, i.e., doesn’t matter whether the bath’s on a perimeter wall or interior to the perimeter and
  • Shall be rated to deliver
    • Not less than 12 air exchanges per hour
      • Do the math: multiply room surface area in square feet times room ceiling height in square feet to get room’s cubic feet, then multiply that cubic feet number by 12 to determine the minimum cubic feet per hour that need be moved to achieve 12 air exchanges, then divide by 60 to determine the minimum cubic feet per minute to qualify for our air exchange metric
  • If you calculate that the minimum cubic feet per minute to qualify for our air exchange metric is within 10% of the nearest product’s maximum, go up a notch in product performance 

• Interior exhaust fan vents shall not exit a residential exterior within 10 linear feet of
  • A soffit vent
  • An operable window
  • A door
  • An operable skylight
  • A deck platform and 10 linear feet above and below
  • A balcony platform and 10 linear feet above and below
  • A walkway or pathway and 10 linear feet above
  • A seating area and 10 linear feet above
  • The horizontal foot print of an exterior staircase and 10 linear feet above and below
  • Any other vent, including a chimney stack
• Preferentially, switch exhaust fans, more particularly, wet area exhaust fans, with a timer, and set ‘em for 20 minutes operation after occupation of that space ends 

• Before The Architect details exhaust fans for each space in a designed home that needs one according to the designers’ standards and judgment. 
• This to follow is an exhaust fan schedule by Before The Architect for a 2-story with detached garage and workshop just south of Boerne, TX 

• There are 5 unusual aspects to this exhaust fan schedule 
  • A bog room (a/k/a separate room for the porcelain throne) gets its own exhaust fan in addition to the bathroom space with shower, tub and lavs
  • See how quiet all these fans are.  No more airport runway propeller noise.  Big dif for convenience...if you choose well and schedule these fans before somebody else "whatevers" you
  • Note the high rate of exhaust volume for any of the spaces.  That's part of Before The Architect's air exchange standards way past most others
  • The Utility exhaust is to relieve moisture particularly in “wet hang" and “hot soak" conditions
  • The Grill exhaust is a code requirement local to the jurisdiction of the building site
• Center an exhaust fan on the source(s) of exhaustibles

GENERAL 

• Note that several models of bath exhaust fans include a low-illuminance, night light capacity, the incremental noise of which over fan-only units may be offset by other senses of safety and convenience
• Involve an HVAC pro in designing methods and materials for both back-draft prevention and exhaust efficiency in designs of
  • Multiple exhausts
  • Several bath exhausts
  • Fireplaces
  • Kitchen exhausts, etc. and of
  • Long-run exhaust conduit, especially close up to or over the manufacture’s specifications, thereby possibly calling for an in-line booster fan or similar 

• Fan(s) in kitchens
  • It shall be considered indicative that
  • A common rule of thumb for rangetop exhaust fans in commercial applications is 300 cubic feet per minute exhaust capacity per each linear foot of rangetop
  • A commonly applied rule for sizing rangetop exhaust fans in residential application is a minimum 100 cubic feet per minute from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62.  See http://www.automatedbuildings.com/news/jan03/articles/ebtron/ebt.htm

Comment:  In this designer's opinion, ASHRAE’s short by 3 times – this designer goes with the commercial ratings; otherwise, airflow’s not nearly enough for conventional ranges to pull cooking steam and grease and cooking heat and way more than not nearly enough for higher-end ranges for all-the-more BTUs of output. 

• In any case, the range hood shall be not less in width than the
  • Rangetop width and
  • Preferably to 6 linear inches wider, evenly
• Shall be vented to the exterior only
  • Note that exterior does not mean crawlspace
  • Note that exterior does not mean attic
• Shall vent only to atmosphere - outside, outside, outside
  • Not to attic
  • Not to soffit interior
  • not to crawlspace
• Shall have vent pitched down not up to minimize draft when the fan is idle
• Kitchen exhaust fan vent(s) shall not exit a residential exterior within 10 linear feet of

  • A soffit vent
  • An operable window
  • A door
  • An operable skylight
  • A deck platform and 10 linear feet above and below
  • A balcony platform and 10 linear feet above and below
  • A walkway or pathway and 10 linear feet above
  • A seating area and 10 linear feet above
  • The horizontal foot print of an exterior staircase and 10 linear feet above and below
  • Any other vent, including a chimney stack

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