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Community and Q&A

Bathroom comfort

swtjr | Posted in Energy Efficiency and Durability on

In Boston, zone 5A, in a 1100 ft^2 19th century condo.

We’re turning a pantry into a second bathroom, a wetroom. The pantry is in a corner of the house that’s currently pretty cold in the winter. Our home already has cellulose insulation, we spend only about $500/year on heating, and any large improvements would have to be coordinated with other condo owners, so I’m not sure we have much incentive to do a general energy retrofit.

My main question is, will local insulation improvements help with comfort in that room even if we don’t improve the rest of the house? I’ve heard that highly insulated houses are more comfortable even at lower temperatures because the surface temperatures are higher, and I’m hoping that would hold true for a single room, too. I have to have the window replaced anyway (it being a wetroom, the window is considered part of the shower enclosure, so it needs tempered glass), so I was considering an Intus window, and I’m considering asking the contractor to put 1 inch of R-5 foam board behind the tile backer, if code permits.

Also, according to the Sunfrost concept shower page, it helps to have surfaces of low thermal mass material. Our current plan is tile; is there such a thing as low thermal mass tile?


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  1. mackstann | | #1

    Tile not only takes longer to warm up; it is pretty conductive, so it wicks heat away from any body part that touches it. Shower surrounds made of fiberglass, plastic, or similar materials are much more comfortable, in my opinion. Then again, they are generally also considered to be cheaper looking/feeling, and less appealing. Hydronic heat can solve the cold tile floor problem, but if you don't already have hydronic heat, it's not a very reasonable solution for just a bathroom. Electric supplemental heating (floor strip heat, kickspace heater, towel rack, etc.) is inefficient, although if you only run it for a short time every day on a timer, the cost probably won't add up to much.

    Logically, improving the insulation of the bathroom's exterior wall should keep the bathroom warmer and more comfortable. If it's above a cool basement/crawlspace/slab, insulating the floor would also help. If it's not impractical, I would try to install a picture window that doesn't open, as this will eliminate a lot of opportunity for air leakage, especially as the window gets older. Getting rid of the window would help even more, but that's probably not desirable.

    Another point to consider is: where does the makeup air for the exhaust fan come from? If it comes from under a door, it might be a few degrees cooler than if it comes from a jumper vent near the ceiling. I've been contemplating this issue with my own bathroom.

    I think that enclosing the shower, as advocated on that Sunfrost page, would really help a lot in keeping the shower warm. Unfortunately, I haven't been able to find much information about completely enclosing a shower. Steam showers are all designed this way, but they have a steam generator, so it's apples to oranges.

    If you can install a drain water heat recovery unit, you can indulge in the hot water a bit more, and still use less energy than you do now to heat it.

  2. GBA Editor
    Martin Holladay | | #2

    Yes, improving the insulation levels and lowering the U-factor of a window can improve comfort levels in a single room. You are more likely to notice these improvements in a room you spend lots of time in -- for example, in your living room. If you are reading a book in an armchair near a window during the winter, a triple-glazed window will be much more comfortable than a double-glazed window.

    For most people, the Sunfrost discussion of shower comfort is a little over-the-top. Speaking for myself, I go into the shower, adjust the temperature to the level I want, take a shower, step out of the shower, and towel off. How long does that take? It's not as if I'm reading War and Peace in the bathroom, like I am in the living room.

    But if you take 20-minute showers, these comfort discussions may matter to you. Nick is right about thermal mass and tile. The same phenomenon applies to bathtubs. Cast-iron tubs are solid and long-lived, but they suck away more heat from your bathwater than a fiberglass tub.

  3. propeller | | #3

    Like you I valued comfort specially in a shower where our body is much more sensitive to a cold surface. Your reference are accurate that a well insulated low mass surface can be more comfortable in a shower. In our future house we are planning using such a low mass acrylic steam shower. I plan on inserting Roxul insulation between the fiberglass shower and the wall to help keep the surface even warmer.
    Good luck with your project. Marc

  4. user-659915 | | #4

    "If the walls of the shower have a fairly low thermal mass, the shower stall will heat up rapidly so a comfortable shower can be taken even in an unheated bathroom."

    While it's entirely true that low mass materials heat up somewhat faster the effect will not be great with the insulated backer you propose and the Sunfrost analysis is otherwise conceptually flawed. Comfort-wise, so long as you have a reasonable supply of hot water, it really doesn't matter how fast the shower walls heat up, what matters is when you step out wet and naked into the cold bathroom. Brrrr! And if your shower water is only the tepid 90° that Sunfrost recommends that cold bathroom will feel even worse. If you don't believe me, go to England in February and stay in a cheap B & B.

    Yes to maxing out the insulation of the whole room, and consider using a vinyl window with acrylic block panel instead of glass to minimize condensation problems. These are available as operable casements which are tight as a tick and allow for quick and easy ventilation of the whole room in nice weather. And if true comfort is your goal, consider a cosy cork bathroom floor instead of tile.

  5. user-659915 | | #5

    I should add, you might also look at cork as a wall finish in your bathroom (not in the shower enclosure, of course). Cork is an amazing material thermally, hold your hand a half inch from a cork tile and feel the warmth it's giving back.

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