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  1. #1

    HRV With Bathroom Stale Air Pickup???

    I've got a question that I'm a bit perplexed about and I'm hoping that I can get some comments.

    I've got a 2850 square foot area where we will be installing an HRV (new contruction). There are 5 bedrooms, a media room, living room and dining room into which we want to push in clean air. For stale air returns, I was wanting to have one in the master bathroom, one in each of our two full bathrooms and one in our powder room. We will also install one at the top of the stairway for the final stale air pickup. We will also install regular (low noise) bathroom fans in each bathroom for those higher use times (bath/shower, smells, etc.).

    The HRV contractor told me his supply house guys informed him that if we install stale air pickups into our bathrooms we WILL have smell transfer problems. He was told that WHEN THE HRV IS NOT RUNNING (e.g. summer time, when the HRV is on a 20-minute on - 40-minute off schedule, if the HRV breaks down, etc.), there is a risk of smells from one bathroom traveling to one of the other locations where there is a stale air pickup. When my wife heard this, she became adament that she does NOT want to install any stale air pickups within any of our bathrooms. My concern is that the bathroom air will become stale over time if the bathroom (and regular fan) remain unused and there is NO HRV stale air pickup for that bathroom.

    Am I way off base of is the information the contractor received bogus? I asked him and he said that he has never installed stale air pickups into bathrooms for any of his previous jobs. However, he said he would install the system that way if we want it. This is a smart guy when it comes to calculating the installation flow and balancing the system, but I'm look for information from folks with experience having HRV stale air returns within bathrooms or for folks that may know where there may be information about this posted online (at least as far as smell transfers goes)? There is a lot of information that talks about having the HRV pickup air from bathrooms, but nothing about a potential for smell transfer if the HRV is NOT running.

    My question is this: when the HRV is NOT running, could smells from one bathroom travel within the HRV stale air return lines to somewhere else within the house? Remember, this would ONLY occur if the HRV were NOT running. If it's running, there really should be no issue as far as I can tell (logically anyway).

    There really are only a few times that I could think of during which the HRV might not be running. For example in the summer we will most likely turn it off or put it on a very reduced schedule as my wife likes to open windows and doors for ventilation. Or if it breaks and has not yet been repaired. Other than that, I think we'll keep it on most of the time or keep it on a 20-minute ON - 40-minute OFF schedule (city requires 8 hours continuous running each day).

    All questions or comments welcome!


  2. #2
    Join Date
    Sep 2010
    FL Tampa Area
    I have never seen a return air installed in a bathroom for that very reason. I have seen systems that smell pickup has become an issue(outside air intake to close to exhaust outlet).

    In my opinion you do have a good chance of odor transfer, of course running your exhaust fan will help reduce this, but I know I wouldn't take the chance.

  3. #3
    Join Date
    Jan 2011
    With the return ducts running into a common location, you do run the risk of having air migrate backwards IF the bathroom is somehow positively pressured compared to the rest of the space. How often this could be the case, not very often I would think. You could always install inflate-able dampers in the bathroom returns to prevent this.

    Another concern I have, is moisture laden air being returned to the HRV. The HRV can take it, but can the duct work? My parents have a return in their basement bathroom. That piece is rusted to heck, and the house is 7 years old.

  4. #4
    Join Date
    Jul 2008
    Prairie du Sac, WI

    HRV With Bathroom Stale Air Pickup???

    I have a RenewAire ERV in my home (WI) as a central exhaust system. It pulls 75cfm from the general kitchen area, 50cfm from the first floor bath, and 55cfm from the second floor bath. It normally runs 50% of the hour, and on demand 20/40/60 minutes. In summer it runs the same percentage, and when I have a couple windows open (none in bathrooms), I turn it back to 10% run time. This provides hourly clean-out of lingering odors or humidity. I have never had odor transfer issues. The system has to run to work.
    If this was an problem, you could also have bathroom odor transfer issues with a forced air system, since the rooms (including bathrooms) are all connected to each other via supply ductwork.
    Outside fresh air intake should be 10 feet from any outside exhaust.
    If the furnace, A/C, or ERV breaks down, supply houses have parts and service men repair them. Good stuff lasts longer.
    Lingering humidity, low cfm, short (exhaust) run time, and/or low grade metal will hasten grille deterioration. I keep my basement below 45% RH during summer with a dehumdifier.

  5. #5
    Join Date
    Aug 2003
    Some ideas that come to mind:

    Only have stale air pickups in bathrooms. Then who cares if there's a "smell transfer"?

    Make sure that the fresh air intake is far from the exhaust; apply the fix at the cause of the problem. If the intake is too close to the exhaust, smells are just a symptom of a problem that's there whether or not there's something to smell and regardless of where the stale air pickups are.

    Wire the HRV to a dehumidistat so it runs until the humidity goes down. This is good to control mold growth too. If it doesn't go down enough you have other problems. Also run the HRV whenever the bathroom fan would be on.
    -If you won't turn it on then nothing else matters.

  6. #6
    Join Date
    Jan 2002
    East Grand Forks, MN


    Why two exhaust systems when one works well?

    If fresh air is required or needed, you can always skip the piping into the bathrooms.

    I usually tell my customers to go with a Total Exhaust system (ERV and pickup vents; no bath fans).
    Only two house penetrations not 4 or more; and thru the side not the roof!

    These work real good. I've done them and they great.

    Now about that smell; never had any issues. Matter of fact; what's the difference between intakes (duct connections) for ERV/HRV's and supply air (duct connections) vents; would interconnected supply air vents stink up the bathrooms or the rest of the house?

  7. #7
    Thanks for all replies. I agree with everyone about potential smell transfers. Personally, I'm thinking this is a very low chance [if any] - unless there is some reason a bathroom in use becomes positively pressured or another bathroom not in use becomes negatively pressured (I'm not sure how either). I'll mention what's been said here to our contractor. I appreciate all the responses so far - and keep any more comments or experiences coming if anyone has any.

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