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Need ventilation suggestions for remodeled office – it’s too tight!

user-6239952 | Posted in General Questions on

Hi all –

I’ve successfully converted my residential 20×20 garage into a beautiful office and photo/video studio. It’s beautiful and I’m very happy except for one thing: lot’s of off-gassing, VOCs, and chemical smell. I’ve had the windows open for most of the last year and still if I close them, the odors build up over a few hours. Air testing shows high levels of VOCs, and detectable formaldehyde – likely from the spray foam or polyspartic floor covering but hard to say.

With the windows open, my consumer level AIQ monitor says the air is OK, so I’m thinking that adding a good ventilation system might do the trick. I have a ductless mini-spit installed, so this system will have to be added from scratch, i.e. no ducts or other system to integrate into.

I see a lot of people doing bathroom fans or ERV’s like Twinfresh but I worry that they may not be enough for this space. Yes, it’s only 4000 cubic feet (20 x 20 room with a cathedral ceiling) but there really is a lot of offgassing in the room and I want to install a pretty substantial ventilation system.

Another aspect is noise. This is a working video/audio studio, so quiet is a must. My Fujitsu mini-split is quiet enough, for sure, and I have exposed rafters and could easily hang/mount an ERV inside and run some 4 inch ducts with no trouble at all. No cosmetic issues to worry about – there are already lights and wires everywhere up there.

I’ve been reading around this forum and am considering exhaust fants with passive inlets, some through-the-wall ERV’s like a pair of Twinfresh units, and also installing a more beefy ERV up on the ceiling and running 2 exposed ducts to the corners of the room.

Any advice much appreciated. For the record, I am hoping to overpower this system a bit, in terms of CFM, because I have a known air quality issue (confirmed by professionals) and want a definitive solution.

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  1. GBA Editor
    Martin Holladay | | #1

    If cost is no object, the Zehnder HRVs are known to be particularly quiet.

  2. user-6239952 | | #2

    Thank you!

    I would never say 'cost is no object' but there is budget for a soild solution to this issue.

    I have read/heard that the Zehnder HRV's are quiet and reliable, yes.

    I'm trying to find specific noise data about them but haven't found anything yet.

    I would be more than willing to run ducts through the room, box the unit in with a drywalled container, or build a sort of shelf above the raters in the corner to make this work.

    If one of the larger units were quiet enough to be running in the room all the time ,I could mount it up above the rafters and be done. I attached a photo of the space I'm thinking about.

  3. user-2310254 | | #3

    Zehnder is well regarded from everything I've read. A probably more affordable option would be something like the Panasonic Intelli-Balance ERV. (There is a cold-climate version, but you may need to investigate further to see if it will operate when needed in your climate.)

    I have one of Panasonic's simpler, unbalanced ERVs, and it is quiet even on the high-speed setting.

  4. user-6239952 | | #4

    Yes, the Intelli-Balance looks like a good candidate as well, thanks.

    My current concern continues to be noise. It doesn't have to be silent in here, but it needs to be quiet.
    Because of the work, I do here, it's critical.

    There is also the sizing of the unit. Per some estimates I could get away with an extremely low CFM as this is a fairly small space. However, we have known air quality issues in here - i.e. VOC's hover at at 100 to 200 ppb with the windows open, but spike up to 700 ppb or worse if the place is closed overnight.

    So, some extra power will help a lot. This part is really subjective, I know, but better safe than sorry. Also, if I can find a ventilation system that keeps the VOC levels down, I don't have to start ripping out cured spray foam!

  5. STEPHEN SHEEHY | | #5

    Dave: we have a Zehnder hrv. At low speed, it is inaudible even if you stand under it (ceiling mounted). At medium it's still very quiet, inaudible outside the room it's in. At high speed, you can hear it, but we only use high when showering or cooking onions.
    You can get a merv 13 filter which might help with IAQ.

  6. KeithH | | #6

    What about a thru wall solution like the Lunos? I've never used or installed one of these but if you have one big room, it might be a nice solution. Specs list db as 16-26. That seems pretty quiet. They are spendy but then you wont have a lot of install labor etc.

    475 is very friendly; you could call and ask about it.

  7. user-6239952 | | #7


    That's good to hear! Which model do you have installed??


    Yes I looked at those and also the Twinfresh through the wall units. My only concern is that they won't be powerful enough to do the job. I'm struggling to determine what kind of CFM I really need, and because I have a known odor problem I want to err on the side of caution.

    These ERV's that cycle in and out are a mystery to me. If they are cycling every x seconds, does the CFM represent the total amount of air moved, or just the rate that it goes back and forth? What about the transition time?

    And for that matter, how is it that the intake and exhaust can be so close together, on both sides, and avoid recycling the same air? It seems that this must reduce efficiency at least a bit!

    I am considering these solutions, but a bit wary of them, too.

  8. user-5946022 | | #8

    Years ago, one recommended solution was to "bake out" the space to rid it of VOC. The idea was by sealing it up, putting the heat on high and bringing in space heat for 1-5 days you could accelerate the curing and release of VOC's. Then you would air the space out and be done, with lowered VOC moving forward. Not sure if that theory was correct, but it might be worth some research.

  9. Anon3 | | #9

    [Editor's note: I have asked Anon3 to respond by email to a request for an updated screen name (to supply a real name) in order to maintain posting privileges.]

  10. user-6239952 | | #10

    Thanks for this input, everyone. A few thoughts:

    - I am doing a crude experiment to determine how much air I need to move in order to have the room keep up with the emissions and build up of VOCs. I have a window cracked and on the opposite wall, a Holmes window fan which is only running one of the 9-inch blades and on the lowest setting. I have no idea what the CFM is on this thing because they don't publish it, but it's pretty low. In the center of the room I have a Foobot IAQ monitor, which is also crude but enough to detect buildup of VOCs. I'm going to let this run for a few days, just to see if this weak fan can exhaust air to solve the odor issue

    - I've heard of the bake-off approach to offgassing, and have even tried it. But, after around a year of testing I'm fairly certain that these VOC emmissions aren't going anywhere soon.

    - If the little fan can keep up with the smell, I may consider a simpler approach with an exhaust fan and maybe a passive intake - simple and quiet, could work well.

    - If the little fan can't keep up with the VOCs, I will probably consider doing a Zehnder unit, mounted on the rafters. It would be pretty easy to build an enclosure for it to reduce sound further. This would be easier than building an enclosure to put the unit outdoors.

    - if there were an outdoor ERV unit, I'd be very interested in that, though!

    I have very little data to go on so hopefully this little test will give me an idea of what kind of ventilation it will take to keep up with the problem.

  11. Jon_R | | #11

    > running 2 exposed ducts to the corners of the room.

    It's not clear to me which of these is true:

    Ducts across the room are the best solution
    Mixing within a room is adequate and ducts aren't needed
    Stratification limits mixing from low velocity ducts and some type of open fan would provide better mixing

    Sounds like you need open window levels of ventilation, which is a lot. So consider source control methods such as encapsulation or boxing it in and depressurizing that space (as is done with radon).

    Shouldn't be hard to enclose small spaces and put the meter inside to identify the source(s).

  12. Jon_R | | #12

    > If the little fan can't keep up with the VOCs, I will probably consider doing a Zehnder unit

    I expect that the CFM from your ductless window fan exceeds the CFM from a Zehnder.

  13. user-6239952 | | #13

    Yea you might be right. It's keeping up at the moment but that's only 4 hours of data :)

  14. LucyF | | #14

    Are you sure that your problem is not outgassing from improperly cured foam? Is it a fishy smell? A year seems to be a long time to have issues with outgassing.

  15. user-6239952 | | #15

    It's not fishy, no. It smells more like new Ikea furniture. It's definitely possible that the foam didn't cure properly. I am waiting for the results of the isocyanate testing so we might get some info.

  16. KeithH | | #16

    I found CFM on one model of those little twin fans (probably all rebrands anyways) of 1400 CFM. That's a lot compared to an HRV and I would think unacceptable many months of the years.

    Good luck.

  17. user-6239952 | | #17

    Yea I can see that the HRV solution might not move enough air, but at this point I'm considering anything and everything because the next step is to start demolishing walls to pull out cured spray foam, and I'm not even sure that's the source of the odor. It might be the floor, it might be something totally unrelated.

    This has really turned into a tough situation!

  18. user-6239952 | | #18

    We put a meter on a similar fan - same manufacturer, same blade diameter, and same generally poor quality. As I had guessed, it doesn't move that much air so maybe it's still possible to use an ERV to keep the place ventilated.

    This is a very rough test, obviously, and we can't read too much from it, but it seems that running just one side of my window fan probably doesn't move more than 100CFM.

    You can see the test here.

  19. user-6239952 | | #19

    The cheap window fan is handling the VOC odors very well, with a single fan running on the lowest setting, in exhaust mode.

    Again, I understand that my data collection techniques here are extremely crude, but I'm enjoying figuring out the best solution and in this situation, some rough data is a lot better than nothing. Learning about ventilation and trying to use inexpensive techniques to solve this problem is actually the most fun I've had all week.

    What I've learned:

    - I know the window fan can keep the air fresh, but that’s not useful info unless I know the CFM of this crappy fan. I rigged up another crude test with a cardboard hood, a bunch of masking tape, and a handheld anemometer. (see pic). It’s a tiny bit leaky but not too bad. I would estimate that on exhaust mode, running a single fan blade, this fan can move around 300 CFM. My actual reading of the anemometer when held around the end of the cardboard duct (exactly 12 inches square) is around 235.

    - I think the air sealing on the room is pretty good. I have the window fan running at one corner of the room, and a small window open in the opposite corner, I get a steady flow of air coming in the window at around 190 CFM+. Given that there are 7 windows, a residential door, and a garage door in the space, and that the intake and exhaust are as far as possible from each other, that seems pretty good to me.

    - Over the next few days, I think I might intentionally obstruct the window fan, and see if I can slowly reduce the amount of fresh air that is entering the space. That way, I might learn what the minimum air flow would be to keep it fresh in there. Unfortunately, the off-gassing of the VOCs (Xylene, mostly) varies from time to time, mostly because of weather, so I will do this very slowly.

    One very interesting finding is that pushing 200-300 cfm of fresh air into the room appears to have nominal impact on the ability of the Fujitsu mini-split to keep the room cool. If I put my hand next to the intake window, I can feel the warm air coming in - it’s in the mid-90’s most days. But, I can set the temp at 65 degrees the mini-split stays on the nearly-silent lowest fan setting and the only way I can tell that it’s even on is that the vents are open.

    This makes me wonder if an exhaust-only system could be a simple and effective solution. With such a small, well-sealed and insulated space, I am already seeing that having 200+ cfm of air didn’t seem to stress the mini-split at all. I certainly understand the idea of saving energy and improving comfort by using an ERV, but I wonder if there would even be much of energy saving in this circumstance.

    With that, a WhisperWall unit might be a little weak - 70cfm is enough to get 3 air changes but is it enough to really keep the room fresh? I doubt it, but something more like 150 to 300 cfm might do the trick, especially if it was variable speed, and I’ve seen some bathroom-type fans like that.

    Anyways, I’m doing my best to get as much info as possible and move forward. If I can install a simple system that runs continuously, and keep the VOC’s down without taxing the mini-split, it’ll be a huge relief.

  20. STEPHEN SHEEHY | | #20

    Dave: have the Zehnder Comfoair 200. It's been in use for about two years and works just fine. Zehnder commissioned it, which I think is essential. When commissioned, it was set at 72 cfm on medium speed, which is where we leave it. Your space is smaller, but as you note, you may want more ventilation, at least until the odors dissipate.
    If you send Zehnder your plans, they'll design the system for you. That was helpful, since the design included all of the various small parts. My electrician said it was easy to install.
    As Keith suggests, you might want to check out the Lunos also.

  21. user-6239952 | | #21

    There's been a development, which is that it's become 100% clear that the polyspartic coating on the garage floor, which was installed when the weather was too cold, is almost certainly causing the odors and is going to be completely removed.

    So, now I no longer have the need to get a higher CFM in order to overcome the VOCs.

    I am really leaning towards a simple exhaust fan with a passive inlet. After weeks of using the window fan to provide exhaust, and cracking a window for intake, I am realizing that the mini-split seems to use nominal extra power to cool the hot air that's brought in through the window, and even with the window fan bringing in 150 cfm of very hot air, the mini-split still stays on the absolute lowest setting and keeps the room very cool.

    So, a simple exhaust system sounds good. While everyone recommends the Panansonic units, I would love it if I could get one that would run at a very low CFM continuously, i.e. 70 cfm, but also have the ability to increase the cfm up to 150 or more if I wanted to freshen up the room.

    Panasonic has some variable speed units, but I can't find one that is easy to adjust (i.e. a wall control for the speed). I do see some Bruan and AirKing units that claim to be equally quiet, but also have a true variable speed feature.

    Has anyone had any luck with any units that might meet my needs? Are the AirKing units considered to be high quality?

  22. Jon_R | | #22

    > leaning towards a simple exhaust fan with a passive inlet.

    IMO, the default configuration should be a pair of fans, one for intake, one for exhaust (ie, balanced ventilation). Your plan will depressurize the space, which pulls moisture into the walls in summer.

  23. user-6239952 | | #23

    Would a passive inlet not handle any pressure issues? It seems like it would correct for that.

  24. user-6239952 | | #24

    When I run an exhaust fan in the window, pushing around 200+cfm, I can crack a window on the other side of the room and feel the air rushing in. Isn't that the same thing?

  25. Jon_R | | #25

    Yes - air rushes in the cracked window because the room is depressurized.

  26. charlie_sullivan | | #26

    Without reading the whole thread, I'm not sure whether pulling air through the walls is a major concern or not. But if you want just one fan and you are worried about pulling air in through the walls, supply-only ventilation would be a better choice than exhaust-only ventilation.

  27. Jon_R | | #27

    Good point - for the summer. Supply fan/passive exhaust in the Summer and turning the fan around (exhaust fan, passive intake) in the Winter would slightly improve wall and ceiling moisture.

  28. Jon_R | | #28

    Without a fan in it, the only thing causing air to enter the passive vent is negative room pressure. But not much (perhaps 1 pascal, depending on CFM, vent size and leaks). That's similar to what summer stack effect does to your ceiling.

    To clarify - your plan will get the space vented just fine. The issue is side-effects.

  29. user-6239952 | | #29

    I'm not sure if I understand the turn this discussion is taking. I see no evidence that significant amounts of air are coming through the walls or ceiling. I do see evidence that some air is sneaking through the seals around the doors but that's about it.

    Also, I'm not sure the room is large enough to have much of a stack effect.

    What I do know is that when I shut the window that I'm using for intake, I the CFM that the window fan can exhaust from the room drops substantially. I can plainly see this with my cheap anemometer.

    So, it seems to be that there needs to be some source of new air. A balanced system seems like a great idea, but simple is also good.

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