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1BadBoy 05-15-2011 09:33 PM

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 saying to have 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!


1BadBoy 05-17-2011 10:42 PM

Bump - anyone? All comments and questions appreciated!

A bit more info is that this house is in Seattle, WA. No air conditioning, just radiant heat. We *may* add paddle fans in select locations (bedrooms, office, media room).

md2lgyk 05-18-2011 07:29 AM

I assume HRV is a heat recovery ventilator? If so, I don't think many people have those (I've never seen one except on television). Folks can't respond if they can't answer your question.

If my assumption is wrong, you need to tell us what the acronym stands for.

1BadBoy 05-18-2011 09:12 AM

You are correct, and I apologize. I assumed (I remember the meaning from high school :) ) that this was a well known acronym.

HRV = Heat Recovery Ventilator

A mechanical means to exchange air within the home. Since we are not installing a forced air heater, nor any air conditioning equipment, we have no venting to meet city codes for fresh air exchange/ventilation. This is the reason for installing an HRV. It's either an HRV or passive vents (no fans) within each bedroom through the exterior wall to allow air to be drawn in when a [bath/laundry] fan is operated - windows are installed and no vents were available for them. Maybe this is the wrong website, but thought I would give it a try. If anyone has any knowledge on the question, I would appreciate any responses.

Thanks for any help!

wilsonstark 06-16-2011 12:30 PM

The government of Canada website sharing information about HRVs notes intakes in bathrooms. The homes I've seen with ERV/HRV ALL have intakes in each bathroom.

I have trouble imagining how smell transfer would happen. In a very tight house the circulation is fairly frequent and it is entirely one-way. Heat is exchanged but the indoor and outdoor air never actually mixes. I suppose if you have someone in your family with profound severe digestive problems and no willingness to courtesy flush then perhaps?

jklingel 06-16-2011 04:27 PM

Run over to and/or I don't think (THINK) you want separate exhaust fans in the bathrooms, as the HRV will draw air back through those fans instead of from the room. Your HRV should exhaust the bathrooms and supply the bedrooms, living room, etc. Kitchens need their own exhaust fans. Also, I think HRVs can be "shut off" and turned on with a switch in the bathrooms, as needed. Let us know if you learn something different from my infantile understanding of HRVs, pls.

creamaster 06-16-2011 07:35 PM

I installed a HRV in my house this past winter and love it. I only have a 1000 sq ft ranch so I didnt bother with a stale air pickup in the only bathroom we have. The air moves well with our forced air furnace.

For your situation however with radiant heat you will want stale air pickups in your bathrooms. I would not however run your HRV and the bathroom exhaust fans at the same time. I would have an auxilliary Timer switch for the HRV installed in each bathroom, so when you need it on high you can press the button and get timed HRV on high. For your summer months you can then use the exhaust fan when the HRV is not needed. You may also think about covering your exhast fans for the HRV months so like mentioned before your HRV doesnt tend to draw air in from these.

jklingel 06-16-2011 09:26 PM

Can't HRVs just sit idle all summer, turned on only when the bathroom button calls for action? I don't understand the problem of not having a separate bathroom fan, and don't see how an HRV in a bathroom would not draw air back through that other fan ducting, therefor minimizing its effectiveness.

1BadBoy 06-17-2011 12:08 AM

Yes, HRVs can, and in our case most certainly will, sit idle (off) throughout the summer months. For us, that's probably about May through sometime into October. My wife loves open windows. We can operate the HRV in one of two ways: 1) always on in a low speed setting so it's constantly exchanging air with a kick up to a higher speed either through remote timers (e.g. in bathrooms) or through the main control panel; or 2) on for 20 minutes an hour and off for 40 minutes an hour. City code calls for a whole house fan (or HRV or equivalent) to run no less than 20 minutes every hour or 8 hours each day. I'm still not sure how we will actually run it, but I'm thinking 20 minutes on, 40 minutes off (could change though once we see how it works and get a better feel for our situation).

But it's those 40 minutes off where the question came up about odor transfer. I have read opinions both ways - no stale air pickups in the bathroom; install stale air pickups in the bathroom. It's about a 50/50 split. As far as odor transfer goes, very few feel it to be any concern at all. As an example, with forced air systems, the furnace normally has venting in bathrooms, and the systems often attach together in runs (2 or more bathrooms and/or bedrooms on the same run), and no one would even think twice about that setup for odor transfer. So most people felt it wasn't worth worrying about. So we decided we'll add them. We are, however, adding dampers where it makes sense as an inexpensive solution just in case.

As for the bathroom exhaust fans, we are also going to add an exhaust fan in each bathroom and laundry room. If for no other reason, we would have a backup during the summers months or if the HRV unit stops and needs servicing. But I think we will use them as needed (and maybe also use the HRV, but not sure here). I wasn't sure about adding HRV timers in the bathroom, but I think we will go ahead and do so as well (no reason not to really). I found a good explanation about how much air is pushed out with an 80 cfm fan compared to the house size and it's not much, but I could not find the site tonight (I'll update this post or add another if I can locate it). So I feel there's very little downside to adding them in now rather than foregoing them and wishing I hadn't later on. Time will tell here.

The parts and pieces of the system arrived today, so we'll see how it goes and functions later on.

jklingel 06-17-2011 01:55 AM

ASHREA specs on ventilation: 7.5 cfm/person, plus 1 cfm/100 sf of living area. For you, that's 28.5 cfm plus 7.5 x (# people), 24-7. Odors floating around in the vents from one bathroom to the other sounds fuzzy; maybe your forced air heat will circulate air enough. ???? But the forced air won't be on much when the HRV is off, so what pressure differential will push farts around? If stink happens, turn on the HRV briefly. You will likely be best off w/ it running whilst people shower, esp if they like long, hot showers. Yes, a quiet fan (Panasonic Whisper Green, or similar) will do the same, but I still don't see how to have a hole in your ceiling and expect the HRV to exhaust properly from the bathroom. Maybe the back-draft damper will take care of that; dunno. But then, how will the fan work properly with the hole the HRV makes; does the HRV have back-draft dampers, too? Either way, I'll find out when I get to that point. Good luck. j

wilsonstark 06-17-2011 02:17 PM


Originally Posted by jklingel (Post 668638)
Can't HRVs just sit idle all summer, turned on only when the bathroom button calls for action? I don't understand the problem of not having a separate bathroom fan, and don't see how an HRV in a bathroom would not draw air back through that other fan ducting, therefor minimizing its effectiveness.

It kind of depends on your local climate. If outside temp is super-hot and you have air-conditioning, you will probably run your HRV at least when you shower and possibly more often depending on indoor humidity. The folks worried about indoor pollutants would say you should run it regularly if you don't have windows open regularly.

At my place, there are usually 20 or so days of the year when the A/C is critically needed and we've got all windows buttoned down tight with blinds drawn. The rest of the summer, late spring and early Fall we wouldn't run either the A/C or the furnace and I suppose it would be idle then aside from showers and cooking.

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