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I tried this once on a cold winter day: I let the bath cool down to room temperature (which was <20C) before letting it drain, with the bathroom door open. The

• lucb1e 4y ago
  But did it even do anything in the first place? Because if the temperature wasn't measurably raised, it's not even worth considering the 'how to deal with humidity' question that people are discussing.
• Someone1234 4y ago
  Although higher humidity should make it feel warmer given the same ambient temperature. So if you're increasing the temperature mildly using this method AND increasing humidity, it may compound one another positively. Although, it is a minor efficiency gain either way.
  • cannam 4y ago
    I thought high humidity made it feel colder, when the temperature was relatively low? Hot damp air feels hotter than hot dry air, but I've had the idea that cold damp air feels colder than cold dry air. Is that a misconception?
    • magneticnorth 4y ago
      I agree with you. Water facilitates heat transfer, and the surface of skin is about 95f, so it seems that below that temperature, and assuming you aren't already sweating for the evaporative cooling effect, humid air should move heat out of your body more effectively than dry air.
    • jtc331 4y ago
      I think “dry” and “damp” are two extremes. I feel warmer in 45% rH at 67°F in winter than at 30% rH same temperature, but the air doesn’t feel damp (OTOH 60% would start to approach feeling damp). That being said, I think at normal conditioned air temperature ranges more humidity virtually always feels warmer. I’m not exactly sure where the cutoff is, but I’d guess below 60°F might be a decent guess?
    • dijital 4y ago
      I think you're right and actually the extra moisture in the air would also mean that raising the temperature of the house requires more energy input since the specific heat capacity of water is higher than air.
  • cameronh90 4y ago
    I'm in the UK, extra humidity is the last thing I'd ever want in winter. At the moment, I've got two beefy dehumidifiers running and I'm still at between 70-85% humidity in each room. I don't have any damp or leaks, it's just that the outdoor humidity has been 80-90% for the last few weeks, so ventilation is futile. And because of the weather at the moment, we're drying clothes indoors.
    • jtc331 4y ago
      What is the temperature outside? Humidity is measured relatively (to how much water air can hold at the current temperature), so even 100% humidity outside at a moderately chilly temperature outside can still translate into uncomfortably dry (e.g., less than 35%) humidity inside.
      • cameronh90 4y ago
        Currently about 17c in the day, 14c at night. At the time of writing, outdoor is 13c and RH is 95%. It was 22c the other day, however it is quite unseasonably warm right now. Once it gets into proper winter weather, normal daytime climate is around 10c-ish and 80%-90% humidity. I've never seen my indoor humidity lower than about 50% without a dehumidifier except after a really long dry spell in the summer or a really cold day in winter. It doesn't often get that cold here, just very damp. Global warming is making winters even wetter. The UK actually has a fair bit of "temperate rainforest" and is classed as a humid temperate oceanic climate.
        • redtexture 4y ago
          What region of the UK are you located in?
          • cameronh90 4y ago
            Inner London, which is going through a bit of a damp period right now after a really dry summer. I'm not sure if those two things are related, but technically we are still in drought even though my garden is basically a swamp right now. My tropical plants are enjoying it though.
• georgeg23 4y ago
  You could place a plastic mat on top to limit evaporation.
  • SnaggyJoker 4y ago
    You could also switch to a water conserving mist shower and reduce the amount of heated water used for the shower. You could also reclaim the water from the shower for use in the toilet by turning the supply to the toilet off and manually transferring it to the toilet tank. There are lots of things you could do to save resources but most things are not done and are not going to be done because it is inconvenient and takes time, and time is money. Edit: now that you have me thinking about this idea, it would be possible to have a container in the bathroom attached to a plug that has a hand pump and a tube going to the drain that could be used to reclaim and hold the water that could be higher than the toilet supply and the pressure from it could be used to have it self fill the toilet tank. The container could be highly conductive material like stainless steel and it could be relatively sealed to avoid humidity issues. This would of course be a vector for illness in some cases.
    • throwaway742 4y ago
      I've noticed that when I put my shower on mist I have to turn the water temperature up quite a bit to have the same felt temperature. The small water droplets seem to cool a lot faster. I'm not sure that it is actually more energy efficient.
    • TrueSlacker0 4y ago
      Combo that with toilet sinks and a lot of water would/could be saved per year/person.
      • SnaggyJoker 4y ago
        The same tank could be connected to the sink too, turning any toilet into a toilet sink.
    • anigbrowl 4y ago
• z3t4 4y ago
  It could also be that your windows are not insulated enough. For 20C and 40RH the windows need to be colder then 6C to get condensation.
  • leoedin 4y ago
    The relative humidity of a bathroom after a shower must be much higher than 40% - I would imagine getting towards 100% (hence room temperature mirrors steaming up). Where I live (UK) I don't think I've ever seen an indoor humidity as low as 40% - it's typically in the 60-70% range.
  • bombcar 4y ago
    Moisture has to go somewhere even if you don't see it visibly condensing on windows. Either it's being absorbed or you have something removing moisture from the system (venting, etc).
    • Maxion 4y ago
      House code in Finland requires mechanical ventilation with vents in the bathroom. I only see brief condensation on my bathroom windows when I leave the sauna door open in the winter (approx. 100 celsius, 80%RH). With good building codes, you won't have condensation issues.
      • hkt 4y ago
        Alas, the UK has the twin problems of poor building codes and lots of old housing stock that nobody puts much thought into maintaining. In the latter case, people will take single skin brick buildings and apply "vapour control" materials outside the building, thus ensuring moisture is locked into the bricks. Then they wonder why they have damp, etc. Alas, we are a very silly country.
        • redtexture 4y ago
          What kinds of material is added to exterior brick? Insulating panels?
• Anthony-G 4y ago
  As a bather, I also tried this idea a couple of years ago. I thought condensation would be an issue but the house I live in seems to have low humidity. The bigger downside for me was having to expend more time and effort cleaning the sides of the bath. This summer, I tried taking cold showers as an alternative energy conservation measure. So far, this Autumn has been very mild in Ireland so I've been able to keep up the habit (I still treat myself to a bath once a week or so).
  • hanoz 4y ago
    It occurred to me to try this for the first time last week and the extra cleaning thing swung it for me too, which is a pity as there's a good 40 pence worth of heat in that water at current prices. Not sure the wife was going to be too pleased with my used bathwater hanging around all day anyway. Also, probably not a very good idea for anyone with young children in the house.
• skrause 4y ago
  Living in Germany and getting both my heating and hot water from natural gas I regulary track my gas consumption throughout the different seasons. With 1-2 showers per day in the household my daily natural gas consumption in winter is about 20x higher than in summer, so compared to heating the house the energy in the hot water is a drop in the bucket.
  • michal8181 4y ago
    Same here (I live in Poland). 2 + 2 family with small kids. Hot water is 5% of my overall gas bills. Rest is heating.
  • SECProto 4y ago
    Note that a portion of that increase in gas consumption is still due to the hot water usage, even if the number and duration of showers stays the same - tap water varies in temperature through the year, getting colder in winter and warmer in summer. In my case, it varies between ~5 and ~22C. Germany has milder winter temperatures so likely not as much variation, but still a significant fraction of the temperature increase imparted by your water boiler. Additionally, if you have a hot water tank (as opposed to on demand), then the tank has to work harder to maintain temperature (assuming you maintain the indoor air temperature differently in winter than summer). All combined, that might account for a 2 to 3 fold increase, the rest of it would be caused by space heating.
    • Retric 4y ago
      Well water stays very consistent year round in most areas. Some municipal systems vary more depending on where they get it and how they store it. Water towers used to smooth out water demand for example can noticeably impact water temperatures.
      • SECProto 4y ago
        Temperature at the well stays consistent, but it can vary at the tap. At a family member's secondary property, tap water will vary from 2 deg in winter up to 15 in summer (because the line between the well and the house is only ~3-4 feet deep, and surface temperature changes a lot). If we were drawing more or less/line was different length/different depth, the variation would change. (I know all these values from homebrewing, where water temperature plays a big role in how long it takes to cool)
• shellfishgene 4y ago
  If you really wanted to do this and remove the moisture problem you could probably cover your tub full off water with a plastic sheet to cool off.
• comboy 4y ago
  Simplest use case would just to have a container in the basement / garage through which the water flows, assuming you are heating it at least a little. You likely keep lower temp there so it is much more efficient. Although in practice drain from the shower or bath quickly connects with the one from the toilet so it's not that easy to implement. In your case efficiency is also slightly lower due to evaporation. If anybody has any idea how significant it is I'd love to learn. I was surprised one day in winter to find that my evaporative humidifier has temp below 10C on it (room temp 23C). I think ground heat pumps could have an exchanger around the main drain pipe which should work nicely both in winter and during summer.
• thinkingemote 4y ago
  My smoke alarms go off.
• hkt 4y ago
  You might have benefited from MVHR, dMVHR, or an EAHP: * MVHR extracts air from "warm" rooms like kitchens and bathrooms, runs it through a heat exchanger to warm new supply air, and then pushes the supplied air into other rooms in the house. It stands for Mechanical Ventilation with Heat Recovery. These systems can significantly increase the efficiency and comfort of your house, provided you also air tighten. * dMVHR is similar, supplying fresh air but reclaiming heat, except the "d" is for distributed. They're like extractor fans but they don't waste the lovely heat. * EAHP is an Exhaust Air Heat Pump. Usually they sit on top of an invented (eg pressurised) hot water cylinder, and they'll take hot, humid air out of whatever rooms you duct them to, heat you water for a quarter of the cost of an immersion heater, then blow cold air out of your house. This is a great option IMO (I have one) but unlike the first two options it depressurises your house and draws cold air in from outside through drafty bits of your house unless you have a corresponding system to warm incoming air at a similar rate to it being expelled. tl;dr there are options to recover the heat while expelling the moisture!
• dev_tty01 4y ago
  We run a humidifier in the winter (Eastern US) because of dry winter air made even worse by the heating process, so this would be a benefit if there is some air circulation to move that moisture throughout the house.