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Condensation on Windows in a 105 Degree Heated Room

svquv9Qkge | Posted in Energy Efficiency and Durability on

Hoping some building science folks might have some good suggestions. I’m helping a contractor friend build out a yoga studio in a commercial space. The yoga that’s going to be practiced there is hot yoga, more specifically Bikram which calls for a room temperature of 105 degrees (yes, you read that correctly. I actually practice Bikram and it’s pretty great).

Anyway, he’s got a good heating contractor on the job who’s worked out getting the room up to that temperature without a glitch. We insulated the drop ceiling a great deal, as well as the walls, and the heating guy ran a baseboard backup system along the one exterior wall of the space to compensate for dropped temperatures due to the two aluminum-frame windows on that wall. We’re trying to come up with a solution to minimize the heat-lost from those windows, as well as the condensation which we both surmise will be great once we hit late winter (we’re in upstate New York, by the way). He’s wondering about sealing the deep window jamb in with a big sheet of plexi-glass and I fear that doing so will just create another plane on which condensation will occur. We can’t cap the aluminum frames from the outside as they’re part of a strip mall and so won’t allow varying the exterior aesthetic. So any solution we come up with has to happen from the inside.

Any ideas what we can do here to minimize heat transfer through the aluminum and window as well as deal with the condensation issue? The windows are about 6-ft. by 6-ft. and the window jam is about 12-in. deep.

Much thanks,

GBA Prime

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  1. svquv9Qkge | | #1

    Here's a quick illustration of the scenario. drawing is incorrectly labeled aluminum "clad" ... window frames are actually not clad in aluminum. they're made of aluminum.

  2. user-626934 | | #2

    Ahh, this is where green building and building science diverge....with Bikram Yoga.

    Believe it or not, the air temperature of that place doesn't matter a lick in terms of condensation. The only things that matter are the amount of water vapor in the air and the surface temperature of the window (frame/glass). What you need most is dedicated dehumidification to control the water vapor coming off all those crazy Bikram-types.

    Running the baseboard heat should help to keep the exterior surfaces warm. If you pull enough moisture out of the air via dehumidification, it's "possible" that you won't need to make any improvements to the windows.

  3. svquv9Qkge | | #3

    Interesting. Thanks so much, John. What you said makes complete sense. Unfortunately it's unlikely they're going to do any dehumidification when many studios actually ADD moisture (adding to the insanity of the heat). Would putting plexi up on the wall to create a dead air space between it and the window do anything helpful? There is an air register above each window (main heat source); the baseboards are just to supplement that side of the room. I don't think they'll actually heat the window up at all as they won't be running that long (classes are only 90 min long).

  4. GBA Editor
    Martin Holladay | | #4

    Adding an interior storm window will certainly reduce the chance of condensation on the innermost pane, which in your case would be the proposed piece of Plexiglas.

    However, you should be wary of this solution. If you leave the Plexiglas in place all winter long, what may happen is that you'll get condensation on the main window behind the Plexiglas (since this window is colder than ever). In some cases, water accumulates at the bottom of the main window and dribbles down to the stool, leading to stains, mold, or even rot.

    If the Plexiglas is easily removable and is only used when necessary, this may be a good solution.

  5. user-1140531 | | #5


    I assume that the window jamb is sheetrock on framing carried out to the wall, which is also sheetrock on framing. If there is no other effective vapor barrier there, vapor may move through the wall and jamb by diffusion and gain access to the cold window and frame despite having the window opening covered with a sealed sheet of Plexiglas. Just stopping the airflow may not be enough to prevent the vapor access to the window when you have a humidified space heated to 105.

    For that matter, such high vapor pressure in the conditioned space raises questions for the entire room structure, and not just the windows. If I were the owner of the building, I would not allow turning the space into such a specialized hot space without a thorough engineering analysis and approval.

  6. GBA Editor
    Martin Holladay | | #6

    A few hours a week of Bikram yoga, and you conclude, "If I were the owner of the building, I would not allow turning the space into such a specialized hot space without a thorough engineering analysis and approval" ?

    Relax, Ron. I think there are more pressing engineering emergencies that need your services than those at this yoga center.

  7. user-1140531 | | #7


    I deal with engineering emergencies on a first come, first served basis. Who said it was only a few hours per week of yoga?

    If they have already modified ceiling and walls, plus added extra heat, I suppose the building owner is approving the whole thing.

    But raising the room temperature to 105 degrees of one room in a building complex in a cold climate zone, and then humidifying that room besides seems like it could cause more issues than just frosty windows.

  8. GBA Editor
    Martin Holladay | | #8

    Chris isn't humidifying the building; he said that OTHER yoga centers sometimes do that.

    All he has in this building is a bunch of sweating yoga students.

  9. user-1140531 | | #9


    You are right that Chris did not say they were going to add humidification. I was just going by Chris saying this, suggesting to me that humidification is desireable, and therefore might be under consideration:

    "Unfortunately it's unlikely they're going to do any dehumidification when many studios actually ADD moisture (adding to the insanity of the heat)."

    It suggests to me that people practicing Bikram yoga like it humid as well as hot. I am not sure how much sweat is worked up during Bikram yoga.

  10. svquv9Qkge | | #10

    Thanks Ron and Martin for the input. I appreciate your perspectives and expertise. It's true that the space is part of a bigger building, but all first-floor (so no one above), and significantly-thick fire walls between the studio and the adjacent spaces. From what I've seen each side of the 2x4 metal-stud wall is rocked with 2 layers of 5/8 sheetrock (I think it's 5/8). Seems are staggered and finish taped. The wall cavity is filled with fiberglass batt insulation. The room won't be heated to 105 more than a couple of hours in the morning and then sometimes again on certain days again in the evening. These Bikram yoga studios are all over the country - the world even, very popular in urban settings. Most of the stuidios are part of a larger building so they're sharing walls and sometimes ceiling/floors with other tenants. I don't know what kind of issues anyone has from your point, Ron, but I'm confident that in this scenario my friends who own the studio won't have any problems. Actually, Only one wall in the studio is shared - the others are part of the rest of their space where locker rooms and a lobby are.

    Anyway, Martin - thanks for alerting me to the increased condensation issue should we proceed with the plexi. I talked with him and he's going to convince the studio owner (his wife) that we should actually cover them and insulate them. We'll build out some contraption that insulates and air seals up to the interior wall's finished surface plane. From the outside the windows will remain though they'll appear black. Seems like the smartest solution, and may even make the baseboard unnecessary (there's actually a 5-7 degree drop in room temp near the windows because of them). So thanks again.

    And as a side note, if anyone is looking for a good gig - designing these heating systems to be programmable would be a money-maker in certain parts (or even a heating system that can do this stuff on its own; most of what we've seen requires a couple of systems together). On that note, consulting to make these spaces work efficiently might be marketable too.

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