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Bathroom efficiencies: Is there something we’ve missed?

user-669103 | Posted in Green Building Techniques on

So we are rebuilding a bathroom here’s some of the efficiences that are planned:

* Water sense shower & faucets
* Dual flush toilet (not water sense). We want it to be wall hung we have only found Toto Aquias
* Exhaust routed via ERV with humidistat trigger and timer
* A heat recovery drain for the shower
* Delta Touch 20 faucet to be able to touch control the water and hopefully waste less water especially hot water (and battery operated to avoid phantom loads).
* Two level CFL lighting
* 1.5″ of XPS on ceiling before putting new gypsum board (as attic has limited capacity for upgrades). Didn’t want to use polyiso in bathroom because it soaks water.
* Also a lot of recycled materials

Hot water is from solar thermal. Electricity is from PV.

If there’s any area we’ve missed please advise, especially in terms of efficiency.

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  1. GBA Editor
    Martin Holladay | | #1

    1. Hot water storage tank is located within 10 feet of the bathroom fixtures.
    2. The diameter of hot water supply lines is as small as possible -- 3/8 in. to lavatory and 1/2 in. to shower.
    3. All water pipes are insulated.

  2. user-669103 | | #2

    thanks Martin....

    I had 2 out of 3 of those covered.
    But had forgotten about keeping hot water pipes small (and the cold shower supply on the warm side of heat recovery unit).

  3. user-939142 | | #3

    a hot water recirc, switch activated, so you don't run cold water down the drain wating for hot water

    this may not pan out cost wise, and i'm guessing could be a pain say for the sink, but should be easy to get use to pushing before turning the shower on. i've seen some motion activate ones too, say for when you enter the bathroom

    note: heat recovery drains supposedly work better routed back to the hot water tank to get maximum flow

    reusing grey water to feed the toliet. all kinds of systems for this. there is one that uses the sink drain to feed the toliet if you don't want a whole house system

    light the room with a solar tube / maxium daylight use to avoid electric lights

  4. kevin_in_denver | | #4

    How are you heating it?

  5. user-669103 | | #5


    The house is heated with geothermal heat pump - to forced air, and solar PV.
    We also have a solar thermal (not plumbed in yet) for potable hot water that will provide most of the hot water in summer, and in winter the heat pump provides most of the hot water, electrical resistance for if neither can forfill demand. (I could use a better control system here).

    I posted separately that we are considering 25 sq ft of electrically heated radiant floor in the bathroom. The aim is to use it for no more than 20 to 30 minutes a time (0.1 to 0.15 KWh).
    While using electricity for resistance heating is not good it is only expected to be used occassionally, and it avoids turning on the bigger heat pump to boost the air temp.

    My trouble with the heated floor (if we do it), is finding a way to avoid heating a larger thermal mass than necessary. I only want to heat the tiles, not 3/4" of mud/concrete too.

  6. kevin_in_denver | | #6

    Just thinking ahead--

    The tile in the bathroom is one of the most likely items to be remodeled in 10-30 years. (Water damage around the tub typically sets off a domino effect). I don't think that your electric resistance infloor heat will survive the demolition process.

    Also, as you say, since the bathroom is only in use for a short time, heating the thermal mass is wasteful. The Panasonic Whisper Warm combines heating and ventilation in a quiet package, but you'd rather have the heat down at the floor. A very economical option would be an electric kickspace heater. Putting it on a timer that kicks it on 5 minutes before the alarm clock goes off would be another affordable luxury. Another advantage of heating the air, not the tile, is that warm air holds more water vapor, so the window and other cold surfaces are less likely to cause condensation.

    I also recommend a bathmat as was suggested on the other thread.

  7. kevin_in_denver | | #7

    One last recommendation-- I know you don't have the room for it, but a completely enclosed prefab shower stall has several advantages:

    1. All the excess humidity caused by showering basically condenses inside the shower itself - which eliminates the need to run the exhaust fan and reduces the chance of mold elsewhere.
    2. The heat from the shower water heats up the shower stall, which could reduce the amount of space heat needed for the bathroom itself.
    3. Long term maintenance is reduced - the biggest maintenance item in a bathroom is keeping the tub to tile caulk line from getting moldy. Showering in the tub causes a lot of water to linger there every day, and there still isn't a caulk made that can handle that abuse.

    Note - I don't recommend tack-on shower doors on your bathtub alcove because they don't completely keep in the water vapor (because of the big gap at the top), and they increase the time it takes to clean the tub area (more nooks and crannies that must be caulked).

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