can bathroom exhaust be interchanged with each other 1

[colonypark]

I have a 44 apartment complex that all baths were vented to the attic (1972). Code is telling me I have to vent outside. I am well aware of grandfather laws but want to comply. Only question is can I hook 10 exhaust to 1 duct going out through roof so I dont have 80 holes in roof?

 

[EEJaime]

Not mech, but I've built some units, I think that as long as you have the fan at the roof and are drawing from the entire system. Your AHJ should be alright with it. You can't interconnect from ceiling mounted fans. I don't know if that is a code issue, but it certainly should be and will definitely be an odor issue.

 

[trashcanman]

EEJaime, where in the International Mechanical Code (or any code) is interconnecting multiple ceiling mounted fans prohibited? I cannot find it. Thanks.

 

[DRWeig]

trashcan,

EEJaime said he didn't know if it was a code issue or not -- but I agree with him, when one fan isn't on (or one fan fails), the others can dump exhaust air backward through the non-working fan into the occupied space. Backdraft dampers to prevent this add complexity and energy to the mix. I prefer one big fan and one big backdraft damper, but that's just my opinion.

Good on ya!

Goober Dave

 

[willard3]

The International Mech code does not prohibit common bathroom ducts, but Engineering judgment should.

Crosstalk in the duct between bathrooms will be a problem and what happens to duct pressure as fans are turned on/off? What happens when a backdraft damper hangs up? What about fire penetrations from different occupancies?

Don't do it.

 

[EEJaime]

trashcanman,
As I stated in my post, that I did not know if it was a code issue. I stated that it should be, because interconnecting multiple ceiling fans is a very bad idea. Exhausting toilet room air into a duct that can enter an adjacent occupancy is not only bad engineering, it is downright rude. Just a common sense approach.
EEJaime

 

[KiwiMace]

I've had this drummed into me to the point where I thought it was a code violation, but skiming through relevant sections, I can't find it. I do agree it is good practice.

 

[ChasBean1]

Goober Dave, good on ya! BDDs or ACDs would be needed here...

 

[sridhar1312]

All the forty four exhaust can be interchanged as long you are ensuring the toilets in negative pressure with respect to exhaust so that exhaust air does not get into the toilet.

 

[DrRTU]

An AHJ adhering to IMC, should not have an issue with combining numerous exhaust fans into a common exhaust vent as long as a back draft damper at each fan is utilized. Make sure the AHJ has not issued a local addenda prohibiting the practice. Venting in the attic should be corrected to minimize water vapor buildup in the attic.

I would inspect the ceiling mounted exhaust fans. The fans may not have back draft dampers or the dampers may be inoperable. A 1972 ceiling fan is at the end of its service life. Broan / Nutone sold tons of axial prop fans in the 70s. Theses fans just made noise and did not move air. The duct condition should also be assessed. The duct may require cleaning. I am assuming this is a multistory building (3-4 stories). We normally combine the ducting in the attic space into one roof vent above a group of fans. Minimize the lateral distance the fan must push the air in the horizontal distance. We do not use plenum dividers inside the roof vent. Adding duct work and a vent hood will add resistance to the fan. You do not complaints from people that the fans to not work after modifications (they may never have vented correctly).

A change in venting may cause an issue with the fire rating of your assemblies. Codes have changed drastically since 1972. Be very careful about shafting and the rating of the units. Various manufactures make a fire damper that fits the inlet grille.

Check the flow rating of the fans. Old applications may have required only 35 CFM per washroom. You should be in the range of 75 to 100 CFM per washroom. I prefer to use a Panasonic or Broan fan.

http://www.panasonic.com/business/building-products/ventilation-systems/products/whisper-ceiling.asp

or

http://www.broan.com/display/router.asp?productID=100226

 

[paultg]

Many of the typical ceiling exhaust fans come standard with BBD. I have connected multiple, but also had a common fan at the roof that always maintained a negative pressure in the ductwork, similar to how multiple dryer exhaust systems are combined by exhausto/kanalflakt systems.

Paul G.