Hot Water Ain't Cheap

When one visits the Breakers in Newport, Rhode Island, the guide emphasizes that the presence of hot and cold running water in the bathrooms was a rare elegance at the turn of the twentieth century, even in opulent Newport. Huge boilers in remote buildings supplied heated water, fresh and salt, for the Vanderbilts to indulge their taste for bathing, itself a rather upscale habit. While water heated on stoves and in fireplaces supplied the needs of Americans for most of our national history, things have moved on. No American home is considered habitable today unless it features a supply of hot running water equal to all the bathing, washing and cooking needs of the family.
I'm not up to a decent history of domestic hot water, but your curiosity may be satisfied by this link.
What I want to talk about is the hot water that serves your residence, and how it can be supplied most economically.
You apartment dwellers may not know what equipment supplies your hot running water; you may just run the hot tap until water arrives from somewhere in the basement, or from a circulating loop that keeps hot water running constantly, waiting for you to need it. Those of us living in condos and detached houses are probably aware that something, a tank, a boiler, or a wall-mount instant heater, supplies the hot water for showers and other uses. And, since the device is likely powered by an energy source that also serves other needs, you probably don't know how much hot water is costing you.
A gallon of cold water at 50 degrees Fahrenheit requires 640 btu (British Thermal Units {one pint, one pound, raised one degree fahrenheit, equals one btu}) to reach 130 degrees, which is too hot for a shower, not quite hot enough for the automatic dishwasher (requires app. 140 degrees to operate efficiently) but hot enough to discourage the growth of bacteria in pipes, and therefore a minimum temperature setting recommended for hot water. If you like your shower to hit your skin at app. 105 degrees, which many people do, you'll adjust your shower control to deliver about 1/2 gallon of cold water for every gallon of hot water, discounting water cooling in pipes and other things engineers care passionately about. If you shower for no more than 12 minutes, you're probably well over 21 years old, and if you have a 2.5 gallon per minute shower control, which you should, you will use 30 gallons of water total, and of that 30 gallons about 20 will be from your hot water source. You just expended 12,800 btu of energy in hot water alone. Your system, whatever it is, is subject to what we will call "engineering losses," which probably range from 20% to 40% of your energy bill. At an average of 30% "engineering losses." including warming the pipes, keeping a tank or a boiler hot day and night, and running the shower before you step in (I know you do this, don't bother denying it), your shower actually expends about 16,600 btu.
If your hot water source is an electric tank, your shower cost about five kilowatt hours at whatever rate you pay for electricity. If your source is a gas heated tank, it cost about 15 cubic feet of gas at your local rate. If your source is an oil-fired boiler, the shower cost about one fifth of a gallon of oil, at your local rate. If your daughter showered right after you came out, that second shower cost you a LOT more than yours. And while you were in there, the dishwasher was running, consuming from 8 to 14 gallons of hot water per cycle, the laundry was running, consuming as much as 25 gallons of water per cycle, about one third of it hot, and your wife washed her hands, you shaved with the water running, and the faucet dripping downstairs let a pint or so go down the drain, all of it hot water.
If the figures make you dizzy, and I have those days, too, you probably spend between $1 and $2 per day on hot water, between teenagers, appliances and your own essential ablutions. You can insulate your pipes, put an extra blanket on your tank, turn down your thermostatic control until showering isn't fun any more, install flow-limiting shower heads that emit a fine spray, and you could save as much as 30% of the energy you spend on hot water. And it might be worth it. Twenty dollars a month is a savings worth calculating, but it won't transform your budget. Conservation is a game of diminishing returns, a struggle noble and brave, but it bores people when you talk about it. In future posts we will revisit this topic and add up the savings of conservation. Our bias then, as now, will be: the American lifestyle uses lots of energy, and the small moves of pipe insulation and tank wrapping are not the answers we need to win the energy wars. Until then, time your daughter's showers, and complain loudly.