I have question regarding problems I am having with the vent fan in a bathroom.

Tim J
by Tim J
I have an older home that did not have a vent fan in the kids bathroom. Last year we added the vent fan, a NuTone 769RL. However, the bathroom (only about 10' X 7' in size) continues to steam-up when the shower is in use. I recently removed the fan to check for obstructions in the vent ductwork, as well as to ensure the flapper on the fan exhaust was functioning properly. All seemed OK. I even got my wet vac and blew air through the ductwork and got up on the roof and ensured it blew-through OK--which it did. Yet the vent fan just does not even begin to remove the steam/condensation. I even tried opening the window and door--and nothing seems to help. Any suggestions? It would seem that that size fan should be completely adequate for this size of bathroom.
  12 answers
  • Designs by BSB Designs by BSB on Dec 29, 2011
    To determine the proper ventilation (IF your ceilings are 8') would be Room Area (Square Feet, widthxdepth) x Constant (1.07) = Cubic Feet Per Minute (CFM). So in your case it would be 70 x 1.07 = 74.9 CFM. So I'd think your fan is proper sized with that formula! The only thing that I would be left to question is the length of the duct <?>
  • SawHorse Design Build SawHorse Design Build on Dec 29, 2011
    Do you leave it running after you take a shower? We recommend putting a timer switch on the fan to help make sure the fan has time to take the extra moisture out of the air.
  • Turn on the fan. Then take some toilet paper about a foot long section. Place it up next to the fan when its on. Does the paper stick to it? Or does it fall down. If the latter happens the fan is not strong enough to overcome the distance of the vent pipe because of friction. There are only a few reasons why the bath fan does not work as it should. 1, blockage, You ruled that out. 2. length of run from fan to outside. Remember every time the duct turns it in effect adds length to the mixture. Meaning if you turn just once at a 90 degree turn you just added about two feet to the over all length of the run. 3. Door not open enough near bottom to allow air to enter into the room. 4. location of the fan is to far away from the moisture source and its condensing faster on the mirror before its drawn out of the bathroom. 5. Additional flapper. Many people install a dryer vent termination fitting on end of bath vent pipe. This type of vent termination has a exterior flapper that must be pushed open by the exhaust fan. Bath fans in order to maintain their somewhat quite operation do not have enough "push" to open the flapper that is or should be installed next to the fan and the 2nd flapper at the end of the exhaust pipe. Remove the one outside. If your concerned about critters entering you can purchase hardware cloth which is a wire mesh, or purchase a new vent termination with a plastic critter screen installed. A quick rule of thumb for sizing the fan CFM is assuming you have a 8 foot ceiling. The results of square foot, length x width would give you ball park in CFM. a six foot by eight foot room 6x8=48 So in theory a 50 CFM fan would be enough to do the work. 50 CFM is the minimum amount of air exhaust suggested as well. Ideally you should go a bit larger. In addition be sure that the vent pipe if its runs into a unconditioned space such as a attic area that the pipe is insulated to prevent condensation from forming inside of the pipe and filling it with water. I have over the past many years removed several gallons of water out of many vent pipes because of the poor quality installation and trapping of water in the pipes.
  • 3po3 3po3 on Dec 29, 2011
    Make the kids take shorter, colder showers. It will toughen them up, and save on your energy bills.
  • Belco Electric Belco Electric on Dec 30, 2011
    Some really good answers here. Steve, I think I like yours the best! The other thing to consider if steaming up a bathroom is a problem is the temperature of the room itself. Condensation takes place when there is a difference in temperature. The greater the difference, the more condensation you will have. Some bathrooms that are not properly conditioned will be colder than others and will tend to "steam up" more. Adding a wall heater in these rooms can make the room more comfortable and help cut down on the amount of condensation that occurs during showering. I also agree with SawHorse, Inc that you need to let the fan run for a period of time after taking a shower to allow all of the moisture to evacuate the room.
  • Tim J Tim J on Dec 30, 2011
    Thanks for the answers, but I'm still hoping for more ideas.
  • When you say the room steams up even with door or window open. Are you saying the mirror is steaming up? Have you had tr do you have issues with mold on ceiling or wall? How far away is the fan from the outside discharge point? Is the pipe insulated? Does it run through unconditioned space until it vents outside? All this can help troubleshoot your issue. But working blind on information is only guessing at this point.
  • SawHorse Design Build SawHorse Design Build on Dec 30, 2011
    I just re-read the complaint. If the issue is the bathroom steaming up when in use, that is to be expected. The problem would be if the moisture continued to linger after the shower was turned off. Woodbridge just asked some good questions that will give him enough information to answer your question.
  • Nip Tuck Remodeling Nip Tuck Remodeling on Jan 01, 2012
    There are some good answers here. Woodbridge starts with a good first check..see if the fan is sucking air. Most problems with fans are that they are underpowered for the room or are not vented properly. Personally, I have always recommended the Panasonic Whisper Fan with a 30-60 minute timer. Even though an 80 cfm fan is technically good enough, I will typically install a 110cfm. You need to run the fan for a minimum of 30 minutes when you are finished to move the moist air - or, as Steve suggested, shorter showers and tough love.
  • Sherrie S Sherrie S on Jan 01, 2012
    I have to agree with all experts. I, too, thought my room was too hot & steamy after my shower - I like the shower quite hot. My fan didn't seem to clear things up quickly. So I bought an inexpensive thing that shows me the temp & relative humidity in the room. What I understand is: Humidity between 29 & 59 is basically OK. There are, of course, optimal areas in between these numbers. It probably takes about a half hour to get to reasonable temp & humidity #'s in my room so my fan seems to be doing a good job.
  • Paul M Paul M on Jan 01, 2012
    Tim I had the same problem in two other houses before, one of which I renovated. After learning that it takes more air movement than I anticipated to keep the steam level down in the winter time I installed dual fans in my current home. One is right above the shower and the other is near the toilet. When I take a shower now I rub both fans and my condensation issues have been eliminated. There is nothing wrong with your fan, it just can't move enough air through your bathroom to eliminate the moisture in the air.
  • Christina Dorrego Christina Dorrego on May 29, 2015
    My kids turn the fan on AFTER the shower, which drives me bonkers. Do yours use it the entire time they are in there? What about adding a heater to heat up the air in there, for dry heat?