Simple Experiments In Heat Reclamation: Part II – The Shower

Increasingly, I’m becoming convinced that one of the keys to keeping the house warm(er) is paying attention to water.

I mentioned before about the huge energy it takes to evaporate a gallon of water– 2.5 killowatt hours. That got me thinking about the fate of water around the house.

The conclusion I’ve come to: one of the worst things you can do, when trying to keep a house warm(ish) without heat, is to turn liquid water into water vapor, then let it get out of the house in that form. Ideally, any water that enters the house as liquid, should leave as liquid. (Similarly, any frozen water that comes in should leave frozen– or, at worst, liquid.)

Crackpot idea, I know. But think of all the sources of water turning to vapor around the house every day: The dog’s water bowl. Steam from the tea kettle you leave on an extra minute. The simmering tomato sauce. Houseplant soil drying out. Bath towels drying. Dishes drying. Toilet bowls. Mopping the kitchen floor. Wet boots in the entry way. Steam from the shower. Not to mention the humidifier/vaporizer/kettle-on-woodstove that you might have.

And then there’s you, and your housemates. Everyone is constantly churning out water vapor, half through your skin and half through your breath. About a liter a day per person, if you don’t exercise in the house– more if you do, or if your house is hot. In fact, about 25% of your body heat is devoted to vaporizing water– doesn’t that sort of suck? (And don’t forget the dog is breathing, too.)

I think it’s safe to say that by myself here, completely unintentionally, I am probably turning minimum of a half-gallon of water into vapor every day. If my house were completely vapor-tight, after a few days every surface would be dripping and slimy. Luckily (I think), the house is not vapor-tight– so all this vapor eventually escapes outside. It might not do it in one swoop: probably, it first condenses on a cold window, or the toilet tank, or a beer bottle. Then it drips somewhere. But eventually, unless it gets to a drain as liquid, it goes out through a crack as vapor– taking with it that 2.5 kwh per gallon.

It used to be, if I spilled some water on the floor in the winter, I’d half-heartedly sop up the worst of it and leave the rest to evaporate. I look at it a bit differently now… I see the puddle of water and I ask myself, do I want to put that down the sink, or do I want to run the space heater to make it go away? Because that’s what it comes down to.

I’m not being nutso about it, but I am trying to eliminate unnecessary sources of standing/evaporating water around the house. Putting lids on soup pots, for example. Not leaving dishes with water in them lying around.

But the big potential source of improvement here, I think, is from the shower. I admit to liking a nice hot shower, no less now that the house is Cold. But it does produce a lot of water vapor. Step one: trying to keep the vapor in the shower. A fully enclosed shower stall would be great for this; my old clawfoot tub,not so good. But, throwing some bubble-wrap over the top, with a little temporary duct tape for effect, made some difference– shower is warmer, with less hot water, and less steam in the house after. But still quite a bit.

How to catch the steam, and turn it back into water, to make it give back its heat? Various ideas. Simplest: mop it up from where it condenses, before it can dry. I took a sponge to the bathroom window post-shower this morning, and with 10 seconds of effort I squeezed out 50ml of water. That represents the heat of a 35W bulb for an hour. Plus, Cat could see out the window for the rest of the day. The mirror netted some, too. If I had two or three more windows, I expect most of the steam would’ve wound up there.

But you don’t want to go installing extra windows to try and keep more heat in– that’s backwards. You need something that’s already in the house, is coldish but not connected to outside, has a smooth surface, a high heat capacity, a high thermal conductivity, and can be kept up towards the ceiling where the vapor rises. Granite and marble aren’t conductive enough. Something like a slab of copper or aluminum would be good. Silver would be perfect, but pricey. My fantasy image is a border around the top of the walls made of plate copper, with a little gutter under it to catch condensed water and deliver it to drop into the sink. If the room is cold when you start the shower, I think this could be designed to catch, condense, and dispose of most of the steam.

There is a simpler but less elegant solution at hand: a dehumidifier. I tried running it during a shower. First attempt was no use: it was on the floor, and the humid air was not.


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