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Dynomight suggested [1] recovering the heat from hot showers by showering with the drain stopped and letting the water cool to room temperature before draining

Dynomight suggested [1] recovering the heat from hot showers by showering with the drain stopped and letting the water cool to room temperature before draining it. I remember thinking it was interesting at the time, but I have not tried it (my shower has a low lip so it couldn’t hold very much water). [1] https://dynomight.net/hot-water/ https://dynomight.net/hot-water/

fbdab103 3y ago
Being a cheapskate, I did this when I lived in Chicago winters. My concern was sometimes I would forget to drain the water. I was creating a big thermal mass which my heater would have to work to maintain at equilibrium. This also has the benefit of potentially raising the indoor humidity, which is otherwise going to be quite dry.
- mcbishop 3y ago
  But in some areas / seasons, the added humidity is a negative.
  - wolpoli 3y ago
    Added humidity is definitely a concern. Perhaps we could fix that by covering the water with plastic to prevent evaporation, but I never look into it.
    - hinkley 3y ago
      Probably not in Chicago in the winter though.
    - whereistherub 3y ago
      Water is a necessary evil regarding buildings, in general.
      - mcbishop 3y ago
        But it can be managed, to mitigate mold and decay.
- krisoft 3y ago
  > My concern was sometimes I would forget to drain the water. I was creating a big thermal mass which my heater would have to work to maintain at equilibrium. Is that a bad thing? I honestly ask. I'm twisting and turning the idea in my head and can argue in both direction. I guess it can be a bad thing if you live by letting the interior go to cold frequently and then try to heat it back to room temp. For example if you would turn off the heating for the day, and then try to heat it back up from near freezing to room temp. That would be bad in itself, and the the extra mass would make it worse. But if it is just maintained near the room temperature point then it is not that clear to me if it is bad. Would be happy to hear either way.
  - fbdab103 3y ago
    The more I think on it, the less certain I am one way or another. From a real-world standpoint, I would lower the thermostat say 15 degrees F during work hours, so re-heating that water when I return seems like it would be a definite negative.
    - akovaski 3y ago
      It might help to think of the tub of water as a heat battery/capacitor: the energy you put in is the energy you get out. So, yes, it will slowly absorb energy when you are heating the room. However, it will also release an equal amount of energy as the room cools down. On that front I'd say it equals out. Technically the tub of water will change how fast the room changes temperature. Because the difference between the room temperature and outside temperature affects the rate that energy escapes the room, this could affect how much energy the room emits to the outside. For example, imagine that you had so much water that the room only went down to 65 degrees F throughout the day; that means that you put enough energy into the bath battery to heat the room to 65 degrees F throughout the day. The other way that you would be consuming extra energy is by evaporating the water. At <70 degrees F and little air circulation, I don't imagine that evaporation is consuming a lot of energy. A bath tub of room temperature water doesn't seem like it would be very effective as a swamp cooler. My guess is that a bathtub of room temperature water wouldn't measurable affect your heating bill.
    - 3y ago

fbdab103 3y ago

Being a cheapskate, I did this when I lived in Chicago winters. My concern was sometimes I would forget to drain the water. I was creating a big thermal mass which my heater would have to work to maintain at equilibrium. This also has the benefit of potentially raising the indoor humidity, which is otherwise going to be quite dry.

mcbishop 3y ago
But in some areas / seasons, the added humidity is a negative.
- wolpoli 3y ago
  Added humidity is definitely a concern. Perhaps we could fix that by covering the water with plastic to prevent evaporation, but I never look into it.
  - hinkley 3y ago
    Probably not in Chicago in the winter though.
  - whereistherub 3y ago
    Water is a necessary evil regarding buildings, in general.
    - mcbishop 3y ago
      But it can be managed, to mitigate mold and decay.
krisoft 3y ago
> My concern was sometimes I would forget to drain the water. I was creating a big thermal mass which my heater would have to work to maintain at equilibrium. Is that a bad thing? I honestly ask. I'm twisting and turning the idea in my head and can argue in both direction. I guess it can be a bad thing if you live by letting the interior go to cold frequently and then try to heat it back to room temp. For example if you would turn off the heating for the day, and then try to heat it back up from near freezing to room temp. That would be bad in itself, and the the extra mass would make it worse. But if it is just maintained near the room temperature point then it is not that clear to me if it is bad. Would be happy to hear either way.
- fbdab103 3y ago
  The more I think on it, the less certain I am one way or another. From a real-world standpoint, I would lower the thermostat say 15 degrees F during work hours, so re-heating that water when I return seems like it would be a definite negative.
  - akovaski 3y ago
    It might help to think of the tub of water as a heat battery/capacitor: the energy you put in is the energy you get out. So, yes, it will slowly absorb energy when you are heating the room. However, it will also release an equal amount of energy as the room cools down. On that front I'd say it equals out. Technically the tub of water will change how fast the room changes temperature. Because the difference between the room temperature and outside temperature affects the rate that energy escapes the room, this could affect how much energy the room emits to the outside. For example, imagine that you had so much water that the room only went down to 65 degrees F throughout the day; that means that you put enough energy into the bath battery to heat the room to 65 degrees F throughout the day. The other way that you would be consuming extra energy is by evaporating the water. At <70 degrees F and little air circulation, I don't imagine that evaporation is consuming a lot of energy. A bath tub of room temperature water doesn't seem like it would be very effective as a swamp cooler. My guess is that a bathtub of room temperature water wouldn't measurable affect your heating bill.
  - 3y ago