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Necessity of Temperature Control of Bathrooms?

steve_smith | Posted in General Questions on

Let me preface this by saying I’m not a professional.  I have read lots here and a few other places.  If this is a silly questions, I’m sorry, but please be patient with me.  I keep coming across concerns about heating and cooling bathrooms and closets in mini split retrofits.  Is this a comfort concern or is this a question of air quality/building longevity/something else?  I would think bathroom doors tend to be left open more often than not and temperature wouldn’t be too variable in that use case.  A walk-in closet is more likely to be left closed more often than not, but a little bit too warm or too cold closet doesn’t seem like a significant problem to me.  I ask this question from the standpoint of someone who lives in a relatively new (<20y) code minimum California home with not huge heating or cooling loads.  Is this primarily an issue with needing to meet the expectations of more particular clients or is there something else going on that I missed and need to take into account?

Edit: Thank your for all the input!  I really appreciate it.  It sounds like for my narrow use case heating and cooling the bathroom is just less of a necessity based on climate (a bit of frost in the morning is a very cold day in my parts), behavior (leaving the bathroom door open), and house design (each bathroom is under 40 sf) than it is in plenty of other situations.

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  1. Jon_R | | #1

    > temperature wouldn’t be too variable in that use case

    Comfort, which depends on the loads and temperatures you want. I prefer the bathroom and walk-in closets to be warmer - which certainly doesn't happen with just an open door (in Winter).

  2. Expert Member
    BILL WICHERS | | #2

    Bathrooms can be an issue around shower time. Stepping out of a shower into an excessive cold bathroom is not fun. I find I really like the combination bathroom fan and heat units, which can be turned on when needed to quickly warm the bathroom when needed, but don't have to be run the rest of the time.


  3. Mark_Nagel | | #3

    Bathrooms are comfort rooms (I'm sure someone has said so somewhere!). Lots of ways to add heat if needed. One can use radiant floor heating (there's electric) or radiant panels (electric is also available). I'm going to space heat my two bathrooms (hypothetical build) using hydronic radiant towel heaters (warm towels and warm air! this is also available in electric).

    As bathrooms are used in shorter duration, usually, you want responses to temperature changes to be quicker than elsewhere.

    Ventilation is a separate issue (and depends on your overall ventilation strategy): air exchangers can usually do boost modes for helping turn over air, and moisture, in bathrooms.

  4. Expert Member
    Akos | | #4

    Colder bathrooms also increase the chance of condensation. Cooling house air down by even 10F can significantly increase the RH in the air, that takes a 70F 40% RH house air close to 60% RH which is asking for trouble. This is more of an issue in older houses where corner bathrooms can be cold enough that mold starts growing on outside walls.

    Generally a warm bathroom is good from building science perspective and creature comforts, so it is a win win.

  5. charlie_sullivan | | #5

    Also, a cold bathroom leads to using more hot water during showering--not only running a higher water temperature but also lingering in the shower, dreading stepping out of it into the cold. As well as undermining any prospect for frugal people to turn off the water while soaping up.

  6. Jon_R | | #6

    I use an incandescent heat bulb (BR40) in the shower. It's fast enough to help, but clearly isn't as comfortable as an always heated room that keeps the tile at 75F.

  7. andy_ | | #7

    "I would think bathroom doors tend to be left open more often than not and temperature wouldn’t be too variable in that use case."
    That's definitely not a given. for some people and some cultures that bathroom door is always closed and expect to get reprimanded if you leave it open.
    In our home, the bathroom is pretty small so it doesn't need much heat, even with the door closed, and the shower warms the whole room up rather quickly. We have electric heat in the floor to take the chill off the tile and that's left at a relatively low temp so it's not an energy hog. We have a heated towel bar too, but I can count on both hands the number of times we've actually used it. I suppose if we had the space or budget for a McMansion style bath suite then we'd need more dedicated heat there.

  8. johngfc | | #8

    Our house tends to be both cool and dry (low RH) in winter. We've always had an in-ceiling electric heater. Our current heater is a very quiet Panasonic that also has an exhaust fan with a separate switch. Following the salesman's advice, we put both the heater and fan on timer switches. In 20 minutes it heats our small bathroom to a very comfortable temperature. Preheating before showering dramatically reduces (but may not eliminate) condensation on walls and increases comfort. Both the heater and exhaust are so quiet you really want it on a timer - otherwise you'll forget it's running. 20 minutes is less than $0.05 of electricity so this seems like a very cost and energy efficient solution.

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