Exhaust fan venting

Status
Not open for further replies.
G

Greg1707

Senior Member
Location
Alexandria, VA
Occupation
Business owner Electrical contractor
I will be installing a exhaust fan in a bathroom. The customer wants me to run the duct about 25 feet along the attic floor and up to a cupola at the top of the attic. I am concerned about the maximum effective length of a duct for the fan. I checked the Nutone website and the documentation for the fans do not give any information about maximum distance for the duct. Is there some other place this information is available? Surely, there is a chart showing duct size/length of duct/power of fan = AOK
 
Greg1707 said:
I will be installing a exhaust fan in a bathroom. The customer wants me to run the duct about 25 feet along the attic floor and up to a cupola at the top of the attic. I am concerned about the maximum effective length of a duct for the fan. I checked the Nutone website and the documentation for the fans do not give any information about maximum distance for the duct. Is there some other place this information is available? Surely, there is a chart showing duct size/length of duct/power of fan = AOK
Click to expand...

I always avoid fans in the ceiling unless they are a very short distance. 25 feet is a long way for a fan to push air esp. uphill- so to spreak.

Have you ever installed an inline fan such as Fantech. Put the fan in the Cuppola near where it exits and install insulated duct down to a small grill in the ceiling. There fans are flawless and a fan generally draws air better than it can push air.
 
Nutone's info is quite useful.:grin:

The unit will operate most quietly and efficiently when located where the shortest possible duct run and minimum number of elbows will be needed.
Use a roof cap or wall cap
Click to expand...

Like that helps
 
There's a couple things I have to say about that. First, the IRC actually requires very darned little ventilation in a bathroom. Most bath fans are way oversized with respect to the minimum code requirements. If the bathroom already has a window, for instance, a fan is not even required.

When you size the fan according to the manufacturer's charts (which mirror the HVI guidelines), I try to use the same rules on ductwork length that the IRC gives for clothes dryers. Max 25 feet, and subtract 5 feet for each hard 90. If I need to go longer than that, I jump up to the next size fan if the fan was already exactly sized to HVI guidelines. Chances are pretty good you're already dealing with an oversized fan anyhow. You could use the online ductloss calculator, but you will normally find that it closely mirrors the rule of thumb I just typed.

I think that it is more important that the fan run the recommended 20 minutes after taking a bath/shower than anything else for effective moisture removal. Whether this is accomplished with a humidistat, an off delay timer or any other control means, it doesn't really matter. It is just important that it continues to run.
 
mdshunk said:
There's a couple things I have to say about that. First, the IRC actually requires very darned little ventilation in a bathroom. Most bath fans are way oversized with respect to the minimum code requirements. If the bathroom already has a window, for instance, a fan is not even required.

.
Click to expand...



Minimum requirements are not necessarily what is the best option in a given situation.

Why would you want to open a window in the middle of January, or the middle of July?

In Mass you must have mechanical ventilation window or not. I doubt we are the only ones with this rule.
 
stickboy1375 said:
I dont see how I can do another trade without that license, no different than the duct guys doing electrical, no?
Click to expand...
You probably can't in an over-regulated state. In my state, and perhaps others, the electrician typically does the bath fan and dryer venting. I don't know why, exactly, but it is what it is.
 
mdshunk said:
You probably can't in an over-regulated state. In my state, and perhaps others, the electrician typically does the bath fan and dryer venting. I don't know why, exactly, but it is what it is.
Click to expand...


I've been doing it all my years in the trade as well, but Connecticut now pretty much has a license for every trade, I try to hand that type of work off as much as possible now.
 
stickboy1375 said:
... try to hand that type of work off as much as possible now.
Click to expand...
I would love to do that. It can be a painus in the anus. By the time I get on the job, the tin knockers are long gone and won't be back until finish. I'm not sure how this is done (logistically) in areas where the hvac guys must do the bath fan venting. Perhaps they supply and set the bath fans so that they can go ahead and run the duct?
 
In the apartment buildings we have done we supply, mount, and wire the fan, the tin knockers come along after for the venting.
 
In my neck of the woods, the tinners do their thing before us sparky's, so I usually state in my contracts that I don't do any venting at all. No dryer, fart fans, exhaust fans, ranges, etc. I make it a point to call that to the GCs attention so he can make sure it's in the HVAC contract.
 
stickboy1375 said:
I dont see how I can do another trade without that license, no different than the duct guys doing electrical, no?
Click to expand...

I know you need a license for heating and air but I am not sure that ducting a fan would fall under that license or not. I never do the ducting unless I am called in to replace a fart fan.
 
On a new residence, here what the HVAC guys do is run their duct to where the fan is going to be. The electricians install/wire the fan and tape and wire tie the duct to the fan. The HVAC guys leave the wire tie and tape. If they don't, they come back when we're done.
 
Status
Not open for further replies.
Top