GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Home humidity and hardwood floors

_Stephen_ | Posted in General Questions on

My home in Southern Ontario has a lot of moisture in it.

The hardwood floor manufacturer claims that I should keep the humidity between 45% and 55%,  so I’ve currently set my ERV to run at full speed if the humidity rises above 45%.  However,  my ensuite bathroom,  the humidity is much higher.  It’s regularly sitting at 60%, and after a shower can often hit 70%+.   This has resulted in permanently damp windows in the bathroom with a lot of mold growing on them.

My current answer has been to get an energy star dehumidifier and place it in the bathroom to try and pull down the humidity in that room to 40%.  At 40% there is no condensation,  but there’s obviously an energy  penalty to doing this.

Can I safely lower the overall humidity in the home without damaging my hardwood floors using the ERV?  Is using the ERV a more energy efficient way of dealing with the issue?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Jon_R | | #1

    A dehumidifier can remove moisture and produce heat at a COP of about 2.8 (because it's condensing moisture) - better than some heat sources (ie, could have a less than zero net cost to operate). But my general impression is that the typical dehumidifier struggles below 50% RH @ 70F (so perhaps a lower COP). If an ERV were 100% efficient, it wouldn't remove any moisture. But it's not, so calculations are needed for your specific ERV. My guess: in Winter, the dehumidifier and the ERV are similar in net cost per liter and the dehumidifier wins because it's mostly limited to the bathroom. A HRV would clearly be more efficient.

    Improving air movement between the bath and the remainder of the house would be very efficient (little power, no heat loss).

  2. STEPHEN SHEEHY | | #2

    Have you done what you can to reduce or eliminate the sources of moisture that are responsible for your high levels of humidity? House plants and cooking can add humidity. But this time of year, lack of humidity is usually more common. According to my cheap meter, interior relative humidity in my house in Maine is only 23%. Obviously, you need to run your bathroom exhaust after someone showers. It's hard to avoid condensation on bathroom windows when warm humid air from a shower hits cool or cold glass, but lots of ventilation should take care of that before mold forms.

  3. Expert Member
    ARMANDO COBO | | #3

    I'm going to assume you are using at least a cheap bathroom fan, so my question is for how long? There are time delay switches you can install that allow to turn the light off, but continue running the fan for 15-60 additional minutes to make sure you remove all humidity in the bathroom. Usually you can find those switches for less than $50.
    FYI, I would never run and ERV or HRV in a bathroom, just in case.

  4. _Stephen_ | | #4

    There is no bathroom fan actually. They've instead opted to use the continuous ventilation method, and the ERV is the only fan. It runs 24/7, but this is not enough to pull down the humidity below about 55% in the bathroom on the best of days.

    The ERV cycles between recirculation and exhausting air based on the indoor humidity, and a minimum run time per hour, currently 20 minutes an hour. I could set the ERV to a lower humidity target, but I'm concerned about hurting my hardwood floor. Will a lower humidity hurt my floor?

  5. Expert Member
    ARMANDO COBO | | #5

    ERVs are NOT designed to be used for bathroom humidity control, that is a totally bad use of a good product. I don't know codes in ON, but here in 'merica, we must have an exhaust fan or a window in each bathroom, and I doubt anyone will open a window in the winter in ON, or anywhere else for that matter. Its a simple fix... Install a bathroom fan with adjustable timer. Leave the ERV for central, balanced ventilation for the house. Panasonic have bathroom fans with timers built in.

    1. Trevor_Lambert | | #14

      I've read of plenty of people having installed an ERV/HRV which ventilates the bathrooms. I think it's unlikely they're all from Canada. I believe there is a provision in the IRC for provision of continuous ventilation to bathrooms at a lower rate instead of the switchable bathroom fan. Someone correct me if I'm wrong.

      If you install both a central, balanced system with an ERV, plus bathroom fans, how does the central system remain balanced when you operate the bathroom fans? I can see how maybe this wouldn't be that big a deal in a leaky house, but in a well sealed house, where is the make-up air for the bathroom fans going to come from?

  6. _Stephen_ | | #6

    It's a brand new house. I'm very confident it passed code. They do their whole subdivision the same way.

    It might be new construction moisture making things worse as well.

    Also, no one has yet answered my question: Will a lower target humidity level damage my hardwood floor?

    1. Jon_R | | #18

      While I have no doubt that it's possible, I go well below 35% every Winter and have never had the wood split. But I definitely get seasonal shrinkage (which isn't damage).

    2. Expert Member
      MALCOLM TAYLOR | | #25


      High or low humidity (within reason) won't damage hardwood floors, but as others have pointed out they can influence how much the floor moves. The key to keeping them stable isn't the level of humidity, it is the consistency of the humidity levels over the year. The moisture content of the planks when they were laid will determine whether the floor shrinks or expands when the house reaches an equilibrium once construction humidity has dissipated. After that it's a matter of trying to eliminate swings that allow the wood to take on or release moisture.

      Noticeable damage to wood floors is usually caused by UV exposure (cracking), or different levels of moisture on the top and bott0m of the planks (cupping).

  7. Expert Member
    ARMANDO COBO | | #7

    Hardwood and engineered wood floors need humidity between 35% - 55%. Bellow 35% can lead to dry out and split along the grain. Above 55% can lead to moisture problems, like mold and buckling up.

  8. _Stephen_ | | #8

    OK Thanks, so we'll pull the house down from 45% humidity to 35% and see what that does in the bathroom.

  9. exeric | | #9

    A big +1 for Armando's response in #5.

    1. _Stephen_ | | #10

      I'm not necessarily disagreeing, but the home is still under warranty. I'm not going to start opening up walls as a homeowner unless I have to. There's a few levers I can pull yet.

      ERV is a Venmar E15 ECM model. 67% moisture recovery I think. Very little power draw. It could be turned up as well.

      1. Trevor_Lambert | | #16

        Between 46-62%, depending on temperature and flow rate.

  10. canada_deck | | #11

    - Install a dedicated bath fan for use when you shower.
    - If you are worried about the warranty, you could get someone who is intimately familiar with Ontario code to take a look at your configuration and you may find that they can find a deficiency. Then you have a clear argument for the builder to fix it.
    I don't know if this is up to date or if it is the version that was in place when your house was built but there is some interesting stuff in here:

    On this subject, here is a very comprehensive PDF describing ventilation considerations and it was written with Canadian codes in mind (even references the Ontario building code.) I realize it's not a direct answer to your question about hardwood but you may find some good ideas in there.

    Finally, do you know where they branched off the duct for your bathroom exhaust? The builder may be able to provide you with plan documents that show how that was laid out. I'm not sure about all the codes, but that might give you an easy way to install an HRV dedicated to the bathroom which would have the higher capacity you need for that room. You could even set it to a very low normal run-time and rely on the boost function when you shower.

    Aside from mold on the inside of your window, you may find that you have to regrout your shower more often than you otherwise would if you aren't dealing effectively with that moisture inside the bathroom.

    Another thought: If you can deal with the moisture during the shower (when it is still suspended in the air as water droplets/steam,) it's relatively easy to move it. Once that water condenses onto a surface, then you are trying to get it to evaporate which is a heck of a lot harder. I'm personally a big fan of moving that steamy air out of the bathroom ASAP.

    I'm not an expert here like some of the other posters so take this for what you will.

    1. Trevor_Lambert | | #15

      Bathroom ventilation via whole-home ERV is compliant with the Ontario Building Code.

      Before even considering to install a bathroom far, you have to have a plan for make-up air. Look at the blower door test, or have one done if it hasn't been already. You don't want to de-pressurize the house when you run the bathroom fan.

      1. canada_deck | | #17

        @Trevor Lambert. Although the general idea of using the ERV as the method of ventilating the bathroom is compliant with the code, it has to be done properly.

        There is a good article on this site about the practical implementation challenges that people are seeing in the field in Ontario:

        For example, if he had the system inspected for strict compliance with the code he may find that the duct sizing was incorrect or that too many elbows were used. He could then go back to the builder and say that his problems are a result of poor implementation and that the code (or the instructions from the manufacturer) were not followed and the onus is then on them to fix it.

        1. Trevor_Lambert | | #19

          Yes, it has to be done properly. Things like developed length and duct size should have been examined at the planning and inspection stages. I think a more practical thing to do would be to actually test the air flow at the bathroom vent, and see if it's close to the design value. You can do this with a reasonable margin of error using a garbage bag of known volume and a stop watch. I believe there's an article here describing it, or at least linking to an external description.

          1. canada_deck | | #21

            Yep good idea. You pay a premium for a new house with a warranty. Make it the builder's problem if you can.

            That said, I do believe that there is a very real chance that houses can be built to-code in Ontario under these new rules and still face moisture challenges. If they are going to mandate ERV/HRV for bathroom ventilation, I think they needed to do more to guarantee minimum numbers for air removal during showers (such as the use of dampers on other intakes).

            Who cares if you have a "boost mode" on your ERV if the bathroom door is very tight to the floor and all the other intakes are simple grills.

            Steve: Do you have a reasonable air-gap below the bathroom door?

  11. Deleted | | #12


  12. jberks | | #13

    Hey Steve,

    I am in Ontario as well.

    I am assuming your ERV is set up for suction in the bathroom? I see this a lot in smaller condos where they'll place the recovery unit above the bathroom and it doubles as both the house ventilation and the bathroom ventilation. But I otherwise get it, you're not going to tear up walls. Also you should see of your floors are covered under warranty as well. But that's also a massive hassle to get the builder to A) agree to replace it and B) the actual task of replacing it all.

    One thing to note, ERV's keep the majority of the moisture in. They're theoretically great when you have it for your living space ventilation and have bath and kitchen fans going for the point of use high moisture areas. Not knowing the whole story here, but I'm going to say that using and ERV to ventilate the bathroom was a mistake and an HRV should have been used to actually get the moisture out. I don't have a venmar myself, but I think you can swap out the core to turn it into an HRV if you want to.

    Otherwise your idea of running a dehumidifier should theoretically work, but that is a bandaid solution, and you have a big stupid unit sitting in your bathroom and wasting even more energy.

    Either way, you need to figure it out. You don't want mould in Your house and your floors messed up. Whichever works best for you.

    1. Trevor_Lambert | | #20

      "I think you can swap out the core to turn it into an HRV"
      A really good idea. I don't think you can with Venmar, but it's certainly worth asking.

  13. Jon_R | | #22

    > I'm personally a big fan of moving that steamy air out of the bathroom ASAP.
    A bathroom exhaust fan has several benefits over continuous ventilation. a) it works more quickly. Less time for the moisture to cause problems, discomfort, and condensation. b) it creates more negative room pressure - which keeps moisture out of the walls/ceiling. c) it works with less total air movement (cubic feet/liter). Remove moist air while it's concentrated, not after it's mixed with dryer air. Directly from the shower stall is best.

  14. natesc | | #23

    Just adding another vote to put an exhaust fan into the bathroom that runs on a timer.

    Seems like we are always over complicating things.

  15. walta100 | | #24

    If you have mold growing something has to change.

    I do not think low humidity will do permanent damage to your floor. I have squeaks in my floors when the humidity gets below 40% that go away at 50%. Some people are comfortable with lower humidity I am not one of them. I find 30% to be miserable.

    Many desert homes have wood floors with 20% humidity.

    Since you are under warranty, complain to the builder let him try to fix the problem. I think the best fix would be to install a bath fan and get rid of the moisture at its source. The fact that a home is code compliant does not mean it will be without problem.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |