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custom bath vent fan

KevinHornbuckle

KevinHornbuckle

Member
Joined
Nov 29, 2013
Messages
2
Location
Oregon
I want to custom build my bath vent for a new bathroom. I want it to meet code and I want the inspector to check it off as compliant. The set-up is typical: duct opening at top of shower wall; vertical duct run with air handler mounted in attic just below termination through 6:12 roof slope; ext. vent has mechanical flapper and is properly sealed against water intrusion. Duct in attic is insulated, 6" diameter. Fan is switched with a timer. The fan manufacturer does not specify the CFM output. Local code requires at least 50. Shower is in room its own, but doorway to the rest of the bathroom has no door, just door opening. Bathroom has a window, and shower room has a window, but I don't think that matters. My question is: is the inspector likely to approve the fan based on my calculation of CFM? It has a UL sticker, but no CFM spec. Maybe I could get such from the manufacturer even though it was not produced for the bathroom venting application. Thanks for any suggestions.
 
What is the basis of your CFM? Do you have an anemometer to take air movement measurements? And what expertise do you have in air movement?
 
I doubt that the cfm will be an issue with the inspector. I might be too easy but I've never asked for the cfm on a bath fan.

Hold a lit match near the intake and when it blows out, look at the inspector and declare "This baby's got some sucking power".
 
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This does not answer your question, but . . . you stated you want the installation to meet code. You need fan data [air flow (cfm) and static pressure (inches of water column)] to compare to your calculated pressure loss through the ductwork to prove the fan is adequate. Or as fireguy stated, you need instrumentation to measure air velocity so you can calculate the air flow or a balometer which will directly measure airflow.

Sorry for the short response / non-answer, but I'm heading out to vote. Polls close in 45 minutes.
 
if you do an internet search with the brand and model number you should find specs on it.

so is this for a brand new bathroom ?? a remodel??

not on that side of the inspection, and depending on above answers, I have seen the inspector maybe look at the electrical connections and make sure it is ducted properly, but they are to busy looking at bigger picture items, and being in a house not that critical item.

Plus it is normally switched and owner has choice of turning it on or not on
 
I understand, Mech. It is not just the fan output, it is the total system output. I believe the way the inspectors here look at it is if the ducting is to code, and and mfg. spec meets the min. CFM, then it passes. I can just ask the inspector before he or she comes out, what they look for and if anemometer data would suffice.
 
Get the specs on the fan and that should be could enough

Exhausting from the bathroom is not a high high critical matter
 
2009 IRC R303.3 Bathrooms. Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which must be openable.

Exception: The glazed areas shall not be required where artificial light and a mechanical ventilation system are provided. The minimum ventilation rates shall be 50 cubic feet per minute (24 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside.

Don't worry about the fan if you have an operable window. You don't need the fan.
 
R303.3 Bathrooms. Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet, one-half of which must be openable.

Exception: The glazed areas shall not be required where artificial light and a local exhaust system are provided. The minimum local exhaust rates shall be 50 cubic feet per minute for intermittent ventilation or 20 cubic feet per minute for continuous ventilation in accordance with the California Mechanical Code, Chapter 4.

Exhaust air from the space shall be exhausted directly to the outdoors.

R303.3.1 Bathroom exhaust fans.

Each bathroom containing a bathtub, shower or tub/shower combination shall be mechanically ventilated for purposes of humidity control in accordance with the California Mechanical Code, Chapter 4; and the California Green Building Standards Code, Chapter 4, Division 4.5. Note: Window operation is not a permissible method of providing bathroom exhaust for humidity control.
Click to expand...
This is California so your code may be different.
 
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