Can a bathroom fan be too big?

[DerbyDad03]

If the calculations for a bathroom exhaust fan (cubic feet + equivalent duct length) indicate an 80 CFM fan, is there any issue with using a 110 CFM fan?

[Jon Danniken]

Noisier? More drafty? It will get rid of the stink faster, but if you are leaving it on for 20 minutes, for instance after a shower, while there is still water on surfaces, it will pull more air through the house, so you will use more A/C in the summer and more heat in the winter.

Practically, though, I don't think the specs on bathroom fans are all that tightly regulated, and they are both in the same ballpark, anyway.

Jon

[Steve F.]

For a bathroom one has to consider that while the unit is on the door will most likely be closed. What air flow will the door allow a 110 vs 80 CFM and will that number be sufficient to eliminate moisture (primary purpose) at the rate you desire.

[Ed Pawlowski]

Only problem is it will suck out more heat from your house, but it will also get rid of the stink or excess moisture from the shower faster. I have an 80 CFM and it works for us.

Be sure to get a quiet one. Panasonic has some of the best for noise.

[clare]

I just crack the window an inch before jumping in the shower and there is NO humidity problem (particularly when it's -23c outside)

[micky]

Sure a bathroom fan can be too big. See those tornado pictures where the house is flying away, or the Wizard of Oz. All of that because the bathroom fans are too big.

Rural people who have never had a bathroom fan before get carried away and buy a model much too big.

[micky]

I thought bathroom fans were only required, and maybe only installed, when there was no window. This the first place I've ever lived without a window in the bathroom, and I don't like it.

[nestork]

Not at all.

In fact, when I was replacing bathroom ceiling fans in my building, I went with the NuTone 8832 fan because it was the largest CFM fan I could get from NuTone without having to pay extra for their quieting technology or go to a 4 inch diameter duct.

All of my existing ceiling fans were 3 inch ducts, and so I figured I'd go with the largest CFM 3" duct fan that I didn't have to pay extra for features I really didn't need.

[Ed Pawlowski]

The problem is getting all members of the household to do it. Leave the door cracked open an inch too.

[gregz]

The best for noise is having the fan out of the room. I have one in the attic.

Greg

[clare]

With no humidifier in the house, just cracking the door also works and helps get the humidity in the house up over 15%

[DerbyDad03]

Panasonic was the plan.

I want to replace the current fan with a fan heater combo. I will be running a dedicated 20A circuit.

[DerbyDad03]

They may be required if there is no window, but they are certainly _installed_ in many bathrooms that have windows.

I have a fan now but SWMBO wants a heater also, so I'm replacing it. Yes, I will be running a dedicated 20A circuit.

[trader4]

Certainly all the bathrooms around these parts (NJ) that I've seen that have been built in the last 30+ years have fans in the bathrooms whether they have windows or not.

I don't see any problem with going with the larger fan. It's not like you are making it 5X or something. And as I'm sure you already know, you definitely want to spend a little more for a quiet one. They have displays at HD or Lowes as I recall where you can hear the difference. It's sad too what builders get away with. Here they are building $1mil homes with the cheapest, noisest crap fans. They probably cost about $35. For $50 you can get one that makes half the noise and for $70 one that is super quiet. So, they cut cost on that whole house, 4 fans, by $60 to $140 and the owner winds up with crap.

For things that are more personal preference and easy to change, eg light fixtures, I don't have such a beef with. But a noisy bathroom fan isn't easy to fix. In most cases, you have to rip the ceiling open to replace it. I have recently seen an upgrade kit in one of the stores that fits some models, where you can retrofit it, but I suspect that only fits a small segment of the problem ones. And I don't even understand why the builder thinks this makes sense for them. I'd put in the better fan and then feature that as a selling point, show them that as an example of why you're house is better, etc. There are a bunch of similar things like that a builder could do that I think buyers would appreciate and it would help them sell the house and at a better price.

[bob haller]

I have often wondered why bathrooms with fans dont have a air vent, perhaps in the door to allow air flow when the fan is on?

[philoÂÂ]

Unless the door is the kind used to seal compartments on a ship, plenty of air will get in under the bottom.

[DerbyDad03]

My thoughts exactly. Replacement air is not my concern.

[HerHusband]

Usually, replacement air comes in under a door. For example, a 1" gap beneath a 36" door is equivalent to a 6"x6" hole. Not to mention, most buildings have a lot of air leakage around windows, pipes, wires, and other penetrations. Intake air is usually not a problem.

However, modern structures are usually built tighter than they used to be, so an intake air supply is often required. It's usually part of the heating system, such as an air to air heat exchanger.

Here in Washington state, if we don't have a central heating system, we have to provide fresh air intakes to each living space (bedrooms, and living rooms). Then there must be an exhaust fan to pull fresh air into the building and exhaust the stale air out.

When we built our house in 2004, we ordered our windows with special screened vents at the top of each window. Then the exhaust fan in our laundry room is setup on a timer so it runs at least 12 hours each day to circulate fresh air. We don't see the vents inside the house because they are located behind the blinds.

It seems kind of counter productive that we took so many steps to insulate and seal up the structure of our home, only to have open vents in every room. But the vents do ensure that we always have fresh clean air in our house, with no mold or moisture problems. It was hassle to comply with when we were building, but I've been happy with the system in real life. It's a huge improvement over the stale, musty air in our older homes.

I do have to be careful when lighting our woodstove. If we turn on the range vent before the fire is going enough to create a good draft up the chimney, the smoke gets pulled into the room instead. Thankfully, I usually start a fire before we start cooking, so that's rarely an issue.

Anthony Watson

[gregz]

My bathroom has heat and return vents. Even if the door is shut, air will come in, plus the little underdoor slot.

Greg

[Jon]

Great minds think alike. I installed a full louvered door on our master bath years ago. Works great!