110 CFM Vent Fan

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dar dack

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Sorry, I am not sure where to ask this. I am putting in a basement bathroom and the fan my wife picked out is 110cfm because it has bluetooth/alexa speakers. However, it only has a 4" vent on back, and the ventilation code I could find says 100 is 10' max smooth metal, 125 is X (so no 4" vent), so 110 is probably X as well, Flex is X for 100. Unless:
Exception: Duct length shall not be limited where the duct system complies with the manufacturer's design criteria or where the flow rate of the installed ventilating equipment is verified by the installer or approved third party using a flow hood, flow grid or other airflow measuring device.

I contacted the manufacturer:
Hello,
There is no regulation on this, so the established Maximum is not obtained or tested for. The run should be the shortest run possible to the outside following the basic requirements.
Kind Regards,


I get, you want shortest run possible, but if 4" isn't even allowed, how can you even sell this crap? I guess I"m asking, am I reading the code wrong, is there anything I can do (upsize to 5" past the 4" connection point)?
 

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WorthFlorida

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What is the model number? Is that chart from the installation instructions or code? If it is code it might be for commercial bathroom requirements. If the fan exhaust is 4", then it can be 4" all the way. Getting too long or too many bends will restrict flow but all it means you will no the pushing 110 CU.FT.
 

dar dack

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John Gayewski

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I tell people this all the time. The code doesn't make something illegal to sell, just illegal to use. If you go to a big box store you will find many many many fittings that aren't legal to use. That doesn't make them criminal to sell.

If people buy it, they will sell it. Exhaust fans are something that gets rat'ed up regularly.

Exhaust regulations are starting to make their way into the codes in a more clearly defined way, more and more. When those practices are used more and more you will see these junk fans come off of the market because people will stop buying them. Welcome to the free market (which doesn't really exist and never has).

I have one in my bathroom and it pisses me off to no end. I'm sure I'll get around to changing it soon enough.
 

dar dack

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I tell people this all the time. The code doesn't make something illegal to sell, just illegal to use. If you go to a big box store you will find many many many fittings that aren't legal to use. That doesn't make them criminal to sell.

If people buy it, they will sell it. Exhaust fans are something that gets rat'ed up regularly.

Exhaust regulations are starting to make their way into the codes in a more clearly defined way, more and more. When those practices are used more and more you will see these junk fans come off of the market because people will stop buying them. Welcome to the free market (which doesn't really exist and never has).

I have one in my bathroom and it pisses me off to no end. I'm sure I'll get around to changing it soon enough.
Yeah I'll guess I'll return it and go with a 70cfm non bluetooth fan. I honestly don't understand how a less powerful fan can use same diameter pipe and be ok. Like 70cfm can use like 90 ft 0 elbows 1 termination. Anyways, thanks for response.
 
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