4 inch bathroom vent fan - 3 inch roof exhaust pipe

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Old 05-17-16, 10:30 AM
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4 inch bathroom vent fan - 3 inch roof exhaust pipe

Hi,

I hired someone to install a new Broan NuTone bathroom vent fan (110 CFM, 1 sone). He should have told me that I have a 3 inch exhaust out the roof and the fan I bought was 4 inch. I could have returned it. But he did not tell me and installed it anyway, attaching a 3 inch flex duct to the fan (which requires a 4 inch duct) using only duct tape. The fan is not quiet and makes a slight rasping sound which I really can't tolerate. (When the duct is not attached, the fan is very quiet so it's not the motor).

Can someone please help me with a low cost solution? I do not want the expense of replacing the roof exhaust to 4 inch. A representative at an online store that sells vent fans suggested that I have my installer replace the 3 inch flex duct with a 4 inch one, and, at the roof exhaust, use a 4 to 3 inch reducer. He thought this should not affect fan's operation too much. Do you agree?

Another solution is to buy a 3 inch fan, but the hole in the ceiling has already been cut to accommodate this one. So, if the above fix makes it sufficiently quiet and effective, I would prefer that.

Opinions please!

Thanks,
Vee
 
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Old 05-17-16, 11:11 AM
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The fan may be noisy because of the back pressure, or may be from turbulence caused by using flex duct.

Using 4 inch duct up to a reducer right at the roof may help.

Even better would be using 4 inch rigid duct (not flex) up to a reducer right at the roof, especially if the run is more than a couple of feet. That gives you the lowest resistance and thus lowest back pressure possible short of replacing the roof jack. Flex duct is best avoided.
 
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Old 05-17-16, 01:29 PM
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Thanks much. I had posted my question to Broan tech support and this was their reply:

Thank you for your question regarding ventilation of your exhaust fan. Unfortunately, if your fan has a 4 inch exhaust port, you must use 4 inch duct and a 4 inch exhaust cap (roof cap, or wall cap). You cannot reduce it down to 3 inches. - See more at: http://www.broan.com/products/produc....yUlsSGGj.dpuf

I am not sure what to do.

V
 
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Old 05-17-16, 03:33 PM
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I have reduced 4" fans to 3" lines with absolutely no problem.

You could be hearing turbulence from the reduction point in which case, as mentioned, moving it further from the fan will help.

Or... the 3" vent cap door could be stuck shut or is sticking and not opening fully.
 
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Old 05-18-16, 07:56 AM
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Thanks.

If I do have him use the 4 inch duct at the fan side and reduce to 3 inch at the exhaust side, it is OK to use a flex duct? Or should it really be rigid? At this point, I just want him to do the bare minimum possible and I think the rigid takes more time to install! I don't really have much confidence in him but already paid him.

V
 
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Old 05-18-16, 08:58 AM
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If I do have him use the 4 inch duct at the fan side and reduce to 3 inch at the exhaust side, it is OK to use a flex duct?
Yes to all.

For bathroom fan connections I use insulated flex duct to reduce cold transfer and condensation.

Master Flow 4 in. x 12 ft. Insulated Flexible Duct R6 Silver Jacket-F6IFD4X144 - The Home Depot
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Old 05-18-16, 09:38 AM
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Thanks. Can you please explain why it needs to be insulated? It's going through an attic that is already well insulated and not heated. Or is that external insulation layer to cut down on vibration, and therefore, noise?
 
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Old 05-18-16, 09:41 AM
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Mainly to cut down on condensation, remember it's heated air going out the vent while the attic air is not.
 
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Old 05-18-16, 07:52 PM
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Absolutely to cut down on condensation.

Depending on the way the duct is run..... warm, damp shower air hits the cold duct and will condense and can run back down the duct, thru the fan and into the bathroom.
 
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Old 05-19-16, 11:15 AM
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Thanks to everyone for your responses. Another question: Can anyone tell me whether it looks like these roof vents can accommodate a 4 inch duct? The vent on the left is the one that goes to the bathroom vent fan.
 
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Old 05-19-16, 11:43 AM
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Never seen roof vents like that. Am I the only one?

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Old 05-19-16, 11:54 AM
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I haven't seen any like that either....a picture from inside the attic would be more helpful in figuring out if a 4" duct can be attached.
 
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Old 05-19-16, 11:56 AM
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That's a new one on me also. I've probably painted 1000 roof stacks for various builders and never saw a vent that looked like that.
 
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Old 05-19-16, 12:18 PM
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I had my roof replaced two years ago by AAA homeowner's insurance roofing company. It was an insurance claim. I live in big snow country (Lake Tahoe) but we've been in drought mode. I actually went to the building inspector yesterday to find out whether these were the right vents and they said yes. I also called the roofing contractor and they said these are the kind you use in snow. But, my retired contractor friend said a different kind should have been used. There has never been any sign of water entry in the two years I've had the roof.
 
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Old 05-19-16, 12:51 PM
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Just curios, if you have a chance could you show us a picture of the other side of the vents where the air actually exits.
 
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Old 05-19-16, 06:16 PM
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Those are called..... Snow Splitter Roof Vents

They're actually covers and not really a roof vent.
 
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Old 05-19-16, 07:22 PM
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Whatever they are, both the local building inspector plus my roofer insist they are appropriate! But my retired contractor friend says they could allow water in---though they haven't in the two years I've had them.

I'm not really able to photograph the opening from the inside because I can't crawl up into the attic very easily. I was hoping someone was familiar enough with them to just tell me if they can accommodate a 4 inch duct.

I've lost faith in my installer but he is still coming back on Saturday to fix what he messed up: He used a 3 inch duct on a 4 inch fan and duct taped it on and when it was making too much noise, he was mystified as to why. I didn't know what he had used till later when I saw the receipt for the duct.
 
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Old 05-19-16, 09:10 PM
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Nothing against Broan but I've switched over to the Panasonic line of vent fans. They are a slight bit costlier but are more efficient and extremely quiet.


[h=3]Product Description: Vent flashing and snow guard for 3"-4 Inch plumbing/sewer vent stacks. Also called "cricket vent" and used often on metal roofs to protect sewer ventilation pipes from snow & ice running down the roofs.[/h]So based on that information.... that vent cover will work with 3" or 4" pipe. I would imagine in your case that 3" ? .... possibly PVC pipe..... was used to penetrate the roof.
 
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Old 05-20-16, 07:05 AM
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I just checked the spec sheet for the cricket vent and it says: The top of the cone is slotted to adjust for different pipe sizes. I am really hoping the installer does not have to cut anything to get the 4 inch duct to fit there! I will not allow him to cut anything since I don't trust him at this point!

The Panasonic may be better but honestly, the noise issue was not the fault of this fan. If you don't follow directions and attach a 3 inch duct (with just tape!) to a 4 inch fan, you have going to have noise! I am just mystified that this guy didn't realize what the problem was immediately! I understand that picking up the wrong duct by mistake could happen to anyone. But once you go to install it, wouldn't this be immediately obvious?!?!?!?! (Rhetorical question here- not looking for an answer, necessarily! :-)
 
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Old 05-21-16, 04:02 PM
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Update - still noisy

OK, so this guy put in a 4 inch flex duct, with a 4" to 3" reducer at where it comes out the roof. It is not quiet and still makes a slight rattling sound. I understand that a reducer could make the fan louder than the advertised 1 sone and that is OK with me. I understand that it could make it less efficient and that is OK too. But I don't understand why it still rattles, which I cannot stand. He has now been here three times and I am done with him, but still don't have a satisfactory installation. By the way, this is the second fan of the same model because he exchanged the first one, thinking it was faulty. This is the fan I bought:

NuTone InVent Series 110 CFM Ceiling Exhaust Bath Fan, ENERGY STAR-AERN110 - The Home Depot
 
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Old 05-22-16, 03:16 AM
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If you touch the vent grille doe the rattle go away or change tune? If so, it could be it's not securely mounted.
 
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Old 05-22-16, 07:48 AM
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I tried that and it made no difference. I'll try it again to make sure.

It could be the flap is poorly designed. I am going to call tech support tomorrow to find out if possibly this could be a "known issue" with the model.

V
 
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Old 05-24-16, 07:20 AM
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Thank you all for your input. I called tech support yesterday and the guy I spoke with who seemed very knowledgeable said it is a "known issue." It more than likely IS the flapper. So, the proposed solution is to add some weight to the bottom of the flapper by taping a penny or some adhesive foam there. That's all well and good and I will probably try it but I am not happy with the fact that I've spent extra money on a "quiet" fan, paid someone to install it and re-install it, and still have to deal with it. I am single, female, not 'handy' and not so rich that I don't have other things to do with my money. And now I will have to either crawl up into my attic to detach the duct and put weight on the flapper, reattach it, and hope it works, or pay someone to do it yet again! Sheesh! I'd really like a refund from Broan for the item AND the labor and will start from scratch with another brand!
 
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Old 09-28-16, 02:38 PM
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Vee - I have installed this same fan, and the fix, I think, is easier than you fear. Note that the duct connector (with flapper inside) can best be accessed from the room, not the attic:

a) Remove the vent cover, and disconnect the fan plug to the outlet in the housing
b) Remove 2 screws attaching the fan to the housing.
c) Gently push the tabs aside that held the fan-to-housing screws, and pull down on fan to remove.
d) You can now see the connector and flapper. You can try attaching a weight as you mentioned,
but might be easier to
e) Remove screw attaching duct connector to housing.
f) attach weight to flapper and follow above steps in reverse.

NOTE: I am not certain that the flapper (damper) needs to be weighted. I noticed that, while applying tape to attach the duct to the connector, a little excess pressure on the connector would slightly and temporarily distort it, resulting in the flapper coming loose (one of its hinges would separate from the mating holes in the connector). If this is the case, push the flapper back into place and follow the above steps in reverse.

Good luck, and let us know how this turns out.
 
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Old 09-29-16, 09:38 AM
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Thank you for the tips. I have moved on past this project. I ended up buying a different brand of fan. The installer used a rigid duct. It is acceptably quiet and all is well.

Best,
V
 
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