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Community and Q&A

Efficient shower stall design: Airflow?

Lance Peters | Posted in Lakesideca Techniques on

So I’m kicking around ideas for efficient shower designs. Our master bath will have a shower stall that is recessed with three tile walls, and one glass wall with a glass door panel more or less flush with the side of the bathroom.

The glass wall will have three parts; two stationary panels and a door in the middle.

I would like to have the stationary panels go floor to ceiling and have the door go very close to the ceiling in an effort to reduce the amount of airflow through the shower. This should reduce cold air drafting and make for a more comfortable shower for a given water temperature.

Does anyone have any advise on how much area should be left open at the top of the shower? I’m planning a ventilation return to be located in the shower near the ceiling, so there should be a steady slow flow of fresh air coming in, but I’d like to keep from letting any hot steamy air out. I also don’t want it to get like a sauna and be hard to breathe.

Searching the web only led to designs suggesting the shower should be sealed completely, which I’m not a fan of. I’d like the ventilation return to pull air through the shower to dry it out after use.

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Replies

  1. User avater GBA Editor
    Martin Holladay | | #1

    Lance,
    I don't have enough experience to answer your question. GBA readers?

  2. Charlie Sullivan | | #2

    I have two suggestions.

    1) If you know the airflow you plan for the return in the ceiling (I assume that's for an HRV system or the like?), you can size the gap for a pressure drop that is small compared to the pressure drop in the duct run, so it won't have much effect, or on a simpler rule of thumb like 2 square inches per CFM. (See the comment section in https://lakesideca.info/blogs/dept/musings/return-air-problems)

    2) It might be nice to be able to experiment. One way to enable that would be to have the top of the door lower than you expect you need it, and then have a trim piece above it that you can change to adjust.

  3. Lance Peters | | #3

    Thanks for the replies. Charlie, you are correct, it would be a return for the ERV.

    I think I'll experiment with our current shower and see how that goes. I have a large cardboard box I need to get rid of, so maybe I can fashion a baffle out of cardboard and mount a small computer fan in it to simulate the return air flow.

  4. Steve Knapp CZ 3A Georgia | | #4

    Lance,

    I have the type of shower you are describing in my master bath. Ceiling height is 9 feet, and the shower glass is about 7 feet tall.

    For a short time after we moved in, the shower did not have the glass partition. Just a shower curtain. It was quite drafty and uncomfortable. Once the glass was installed, the experience improved dramatically. When the shower is on and the door is closed, it is quite comfortable.

  5. User avater
    Stephen Sheehy | | #5

    Our master bathroom is 14x6'. No partitions at all. Shower is at one end, floor slopes to linear drain. Once the hot water runs for a few seconds, room is toasty. We run the hrv boost during a shower. Even With two shower heads on, it doesn't get foggy. I think you only need doors to keep water from getting stuff wet, not to stay warm. I suspect anything close to a complete enclosure will be too steamy. We also have heated floor, but often don't bother with turning it on.

    Not having to clean glass doors is a plus.

  6. Lance Peters | | #6

    Steve K.,

    Thanks for sharing. Our house will have 9 foot ceilings as well, minus a service cavity for wiring etc. I'm debating having the bathroom and closet ceilings dropped to 8 feet to facilitate ductwork, plumbing vents and the like. It would be nice to have the ceiling flush through the shower to the rest of the room as well.

    Stephen S.,

    We are in the cold end of Climate Zone 6A. It was -4F Wed. night and -2F this morning. We usually get several stretches of even colder weather in Jan/Feb.

    Part of my motivation to keep the hot humid air in the shower and out of the bathroom is concerns of condensation. We will have a window in the bathroom and I wouldn't want it to accumulate condensation every time we take a shower. I haven't decided on an ERV yet, so a boost mode may or may not be an option. I would like to think we could get by without a boost mode, and a dedicated bathroom fan is not in the plans.

  7. User avater
    Stephen Sheehy | | #7

    Lance: We're in zone 6 also. With a well insulated, tight house and triple pane windows, we don't experience window condensation even at sub-zero temps. In the bathroom, of course we get condensation on the bathroom windows during showers, but running the hrv boost eliminates it pretty quickly. If you want to confine condensation to an enclosed shower, won't you need a big fan to avoid too much fog while showering?

    We have a service cavity above the bathroom ceiling which made it easy to run pex and hrv ducts. By using raised heel scissor trusses, we have high cathedral ceilings. But on the entire north side (kitchen, bathrooms, mechanical room and entry) we have 8'4" ceilings under a service cavity in conditioned space. That made installation of wiring, plumbing, minisplits, hrv, etc. simple.

  8. Lance Peters | | #8

    Great info, thanks for sharing! Looks like our builds will have much in common, minus the cathedral ceilings.

  9. Jan Juran | | #9

    Hi Lance: Larry Schlussler, owner of Sun Frost high efficiency refrigeration manufacturer, has designed efficient shower concepts. Check out his blog summary at:

  10. Lance Peters | | #10

    Jan J., thanks for the link! Apologies for not checking back in on the conversation. All of the benefits that Mr. Schlussler describes are what I was after with my initial idea.

    UPDATE

    So I've been using what I will call my "Shower Air Block" since shortly after I last checked into this thread. It's a piece of leftover coroplast cut to fit the opening above the door. It fills the opening minus about a 3/4" gap at the top. Our current shower is a one piece fiberglass insert style with glass door. The framed opening is about 36" square, so the inside of the shower is about 33" square, and the ceiling is dropped above to about 7 feet.

    I've found everything described in the web page linked to by Jan J. above to be absolutely true. I find when I set the shower water to my usual desired temperature I end up setting back the temperature a bit a few minutes into my shower as I'm getting too hot. There's no steam evident, likely because the air is warm enough to keep steam from forming.

    It's very comfortable! Eliminating that cold air pouring in over the door has a huge effect on comfort. I drape my towel over the door so I can pull it in once done, and I can dry off inside the warm shower so I'm dry when I get out. It really is nice!

    I do have to say that my wife doesn't like it. She complains about getting too hot, to which I obviously reply that she should turn the water temperature down. Her reasoning is she has stiff neck and shoulder muscles and enjoys the scalding hot water feeling to relax them. I can't quite come to terms with this (really???), but I thought it best to have full disclosure here. I have a feeling that her biggest objection is cosmetic, with which I would FULLY agree; this isn't exactly a sexy modification. But hey, it's just a proof of concept.

    After experimenting I fully intend to set our next shower up this way, with a glass door that goes almost tight to the ceiling. I will have a very low flow ERV exhaust inside the shower, so a small amount of fresh air in will be present. That, coupled with the fact the new shower will be about twice the size of our current one, should keep my wife from overheating.

  11. Lance Peters | | #11

    Here’s a picture of the SAB:

  12. Lance Peters | | #12

    So I got playing around with some thermocouples yesterday. The drain for the shower is located in the same room as the water heater so I thought it would be interesting to see if there was a difference in drain water temperature with the Shower Air Block in place.

    I must admit that this was FAR from a scientific test and in the end there were a couple of things working against my getting accurate data, namely the delay between making a change and temperatures stabilizing, and the varying temperature of the hot water supply over time.

    Suffice to say I feel reasonably confident that there was about a 2-3F increase in the drain water temperature with the SAB in place. If we assume a 2.5 gal/min shower head and an 8 min shower, we're looking at somewhere between 330-500 Btu kept out of the house and available to the Drain Water Heat Recovery unit. That's up to 2000 Btu's per day for a four shower/day household, and that's assuming every shower is held to 8 minutes.

    Another large benefit of this approach would be the amount of humidity kept out of the house. Tight homes with high indoor humidity levels could surely benefit.

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