Exhaust fan shutdown over 2,000 cfm

[lielec11]

The NY State Mechanical Code calls for automatic fan shutdown for supply fans over 2,000cfm. I can't seem to find anything that dictates whether exhaust fans (not return fans) have the same requirement. Anyone know the requirement?

Thanks

 

[david luchini]

The NY State Mechanical Code calls for automatic fan shutdown for supply fans over 2,000cfm. I can't seem to find anything that dictates whether exhaust fans (not return fans) have the same requirement. Anyone know the requirement?

Thanks

The NY State Mechanical Code requires shutdown of all operational capabilities of an air distribution system upon activation of a duct detector located in the Return air duct for systems with a capacity of over 2000cfm, unless the system is part of a smoke control system.

No shutdown is required for exhaust only systems.

 

[GoldDigger]

The NY State Mechanical Code requires shutdown of all operational capabilities of an air distribution system upon activation of a duct detector located in the Return air duct for systems with a capacity of over 2000cfm, unless the system is part of a smoke control system.

No shutdown is required for exhaust only systems.

And FWIW, for certain types of exhaust fans, such as those in kitchen vent hoods, there are required not to be shut down, I believe.

 

[lielec11]

And FWIW, for certain types of exhaust fans, such as those in kitchen vent hoods, there are required not to be shut down, I believe.

Thanks for the info guys...

What does FWIW stand for? In this particular instance, it is just a general exhaust fan and a toilet exhaust fan. As far as I know I do not need to tie these into the FA system for shut down. Thanks again.

 

[iwire]

For What It's Worth.

 

[GoldDigger]

Thanks for the info guys...

What does FWIW stand for? In this particular instance, it is just a general exhaust fan and a toilet exhaust fan. As far as I know I do not need to tie these into the FA system for shut down. Thanks again.

For What It's Worth.
Standard internet abbreviation.

 

[mjf]

Standard internet abbreviation.

SIA

 

[topgone]

If my memory serves me right, the provisions in most codes requiring fans to be stopped when fire is detected comes from the idea that running fans might help spread the fire/smoke in the building. If the fan exhausts possible smoke-laded air (discharge ducted outside of the building) , then it does not fall into that fan stopping rule. If it is an air handler distributing air to the various rooms inside the building, then it should be interlocked with the fire detection system and be stopped. My two cents.

 

[mgookin]

If my memory serves me right, the provisions in most codes requiring fans to be stopped when fire is detected comes from the idea that running fans might help spread the fire/smoke in the building. If the fan exhausts possible smoke-laded air (discharge ducted outside of the building) , then it does not fall into that fan stopping rule. If it is an air handler distributing air to the various rooms inside the building, then it should be interlocked with the fire detection system and be stopped. My two cents.

It's to keep from drawing it from the point of combustion and putting it in the means of egress.

Over the years the duct detector requirements have bounced back and forth from supply air stream to return air stream. I believe it settled on return air stream, but you never know, because they change it all the time. You'd have to read your code for your area today.

 

[kwired]

My two cents,

shutting down internal air circulation keeps smoke from being moved from the source to potential egress routes.

For ventilation that brings in external air, you would want to stop that ventilation to help smother a fire, bringing in fresh air gives that fire more oxygen and keeps it going.

Then you have the situation of a cooking hood where if the fire is in the hood, keeping the exhaust fan of the hood running will help contain that fire within the hood or the ducting, shutting that fan off will allow it to spread easier. That particular application you want the fan to run if there is a fire in a hood, but would want the fan to shut off if there is a fire elsewhere in the structure.

 

[lielec11]

If my memory serves me right, the provisions in most codes requiring fans to be stopped when fire is detected comes from the idea that running fans might help spread the fire/smoke in the building. If the fan exhausts possible smoke-laded air (discharge ducted outside of the building) , then it does not fall into that fan stopping rule. If it is an air handler distributing air to the various rooms inside the building, then it should be interlocked with the fire detection system and be stopped. My two cents.

That is how I understand it as well.

My two cents,

shutting down internal air circulation keeps smoke from being moved from the source to potential egress routes.

For ventilation that brings in external air, you would want to stop that ventilation to help smother a fire, bringing in fresh air gives that fire more oxygen and keeps it going.

Then you have the situation of a cooking hood where if the fire is in the hood, keeping the exhaust fan of the hood running will help contain that fire within the hood or the ducting, shutting that fan off will allow it to spread easier. That particular application you want the fan to run if there is a fire in a hood, but would want the fan to shut off if there is a fire elsewhere in the structure.

If it is general exhaust or toilet exhaust that isn't tied into the supply or return air risers I do not see the need to shut them down. If anything, they will help exhaust any smoke out of the building.

 

[kwired]

If it is general exhaust or toilet exhaust that isn't tied into the supply or return air risers I do not see the need to shut them down. If anything, they will help exhaust any smoke out of the building.

Again my $.02 worth of opinion and not necessarily any code - a fire needs a fuel source and it needs oxygen, as well as a heat source to get it started. Take any of those items away and you choke a fire that has already started. Having a fan feeding oxygen to a fire doesn't help no matter how big or small that fan is. Ideally you would like to close off all air sources to a fire if possible at least until fire dept arrives to help minimize the fire.