Bath Air Quality

BEFORE THE ARCHITECT – HOME DESIGNING BACKGROUND – UNIQUE HOME DESIGNING ARTICLES

HOME BUILDING PROBLEMS - BATHROOM AIR QUALITY

Some bogrooms are outside the purview of this article . . .

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hOME BUILDING PROBLEMS - BATHROOM AIR QUALITY

INTRODUCTION

Before The Architect is amazed at how little attention is given in anybody’s home plan to such an important subject as home bathroom air quality

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

BATHROOM EXHAUST FAN DESIGN FOR HOME AIR QUALITY

Fan(s) for bathroom exhaust

Shall be located in each bathroom without regard to that bathroom’s site within the home, 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

Comment: Just to be on the safe side of this series of calculations, let’s do the math together.

Example:

(1) Bathroom is 8 linear feet wide x 12 linear feet deep x 8 linear feet high

(2) 8 linear feet x 12 linear feet x 8 linear feet = 768 cubic feet

(3) 768 cubic feet x 12 air exchanges per hour = 9126 cubic feet per hour

(4) 9126 cubic feet per hour / 60 minutes = 152 cubic feet per minute (CFM)

(5) You’re looking for an exhaust fan that is explicitly labeled to move 152 CFM more or, less preferably, a very little less.

Comment: In smaller bathrooms wherein even 12 air exchanges per hour calculates to a small value for cubic feet per minute. just pick up a desirable fan (with light, with night light, etc) with the closest rating to that low number.

Comment: Note well that light-fan combos tend to be noisier than solo-fan units. This designer specifies fan-only appliances.

Comment: Codes across our fruited plain seem silent about home air pressure affected by exhaust fans and standards thereto. This matter is all the more important as homeowners demand more energy-efficient homes and designers design them tighter and builders build them tighter. This home designer strongly recommends that an HVAC professional install your HVAC system throughout and including exhaust fans, and, that coincidentally, that professional makes a determination as to worst-case negative pressure along with engineered prescription for makeup air.

Comment: In regard to the air exchange rate, that 12/hour rate is way over conventional air exchange rates in the roughly 4-5 range. This home designer is unmoved. Exchanging air every five minutes in a bathroom in active use by an adult or two or a young’n loitering in the shower seems reasonable to me and lesser exchange rates don’t.

BATHROOM EXHAUST FAN INSTALLATION FOR HOME AIR QUALITY

Interior exhaust fan vents shall not exit a home 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

BATHROOM EXHAUST FAN SCHEDULE

	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

Bathroom Exhaust Fan Schedule

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

. . . . . . .

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