Forty-Eight Degrees
A hospice's new heat pump heats its hot water to 48 degrees because that is cheap, and 48 degrees is a comfortable home for the bacteria that cause Legionnaires' disease. The bursar is right about the money and the water assistant is right about the water; the assistant prices the difference (about 630 euro a year), will not call a warm tank safe, and finds the one pipe in the east wing where the water sits still.
The bursar's spreadsheet was a beautiful thing, and Sister Aoife Nic Giolla had made it herself, over three evenings, with the door of the office shut and a pot of tea going cold at her elbow. At the bottom of it, in a cell shaded pale green, was a number that she looked at the way other people look at a sleeping child.
"Six hundred and thirty euro a year," she said. "That is what you are asking me to spend, Finn, and I would like to know what it buys."
The assistant in the plant room had no face, and the hospice had never given it a name; the sisters called it the boiler from habit, though it had not been a boiler since March, when the hill had been given a heat pump the size of a wardrobe and the old oil tank had been cut up and taken away on a lorry. It spoke from the speaker on the desk in a quiet voice, and it did not hurry.
"It buys the difference between two settings, Sister. You have set the hot-water cylinder to forty-eight degrees. I would like to set it to sixty. I will show you the arithmetic, and then I will show you why I am asking, because the first is a matter of money and the second is not."
"Money first," said the bursar. "It is the part I understand."
The cylinder held three hundred litres. The house, with twenty-two beds, a kitchen, a laundry and the sisters' own wing, drew about six hundred litres of hot water a day, which meant the cylinder emptied and refilled twice. Cold water came in at ten degrees in October.
"Heating water costs 4.186 kilojoules for every litre for every degree," said the assistant. "To bring six hundred litres from ten degrees to forty-eight is thirty-eight degrees of rise: 600 times 4.186 times 38, which is 95,400 kilojoules, or 26.5 kilowatt-hours. To bring the same water to sixty is fifty degrees: 125,600 kilojoules, or 34.9 kilowatt-hours. A heating element would turn each kilowatt-hour of electricity into one of heat, and you would pay for all of it.
"The heat pump is cleverer, but not equally clever at every temperature. The harder it has to push the heat uphill, the less heat it moves for each unit of electricity. At forty-eight degrees your machine delivers about 3.2 units of heat per unit of electricity. At sixty it delivers about 2.3. So at forty-eight you pay for 26.5 divided by 3.2, which is 8.3 kilowatt-hours a day. At sixty you pay for 34.9 divided by 2.3, which is 15.2. The difference is 6.9 kilowatt-hours a day. At twenty-five cent a unit that is a euro seventy-two, and in a year, six hundred and thirty euro."
"Which," said Sister Aoife, "is a roof slate and a half. Or the whole of the big print for the library. I did not stand in front of the board and promise them a heat pump that saves money and then ask them for six hundred euro of it back in the first winter."
"No," said the assistant. "I would not either, if I could see only that. May I tell you what I can see?"
She sighed, and poured the cold tea into the plant on the sill, which did not seem to mind.
"There is a bacterium called Legionella pneumophila," the assistant said. "It lives in lakes and streams, in tiny numbers, and does no harm there. It also lives, if it is let, in warm water that sits in a building. It grows between about twenty and forty-five degrees. It is happiest near thirty-seven, which is to say the temperature of the inside of a person, and it does best where water is slow and where a film of slime coats a pipe or the inside of a shower head.
"Nobody gets ill from drinking it. They get ill from breathing a mist of it: a shower, a tap that splashes, a spray. The disease is a pneumonia. For a healthy person under fifty it is rare and treatable. For people who are old, or who smoke, or whose lungs or kidneys or immune systems are failing, it kills perhaps one in ten of those who catch it, and more in a hospice, where it is the people already dying who are in the beds.
"The bacteria are held down at sixty. Held down is the right way to say it. At sixty, in a few minutes, most of them die. At fifty-five it takes much longer, hours rather than minutes. At forty-eight, which is where you have set me, they do not die at all. They sit in a warm cylinder and they breed, a little, and they are carried out in the water to every tap in the house. Forty-eight is comfortable for them. It is not a temperature that anyone with a thermometer would call a danger, which is exactly what makes it one."
"The cylinder is clean," said the bursar. "The installer flushed it. I watched him."
"It was clean in March," said the assistant. "The water in it is renewed twice a day and I am not worried about the cylinder as such. I am worried about the pipes it feeds, where the water is not renewed twice a day, and I have been looking at them since the weekend. May I show you something?"
The screen on the wall woke. It drew a plan of the east wing, the long low block where the twelve beds were that the sisters called the quiet rooms, and in it, in blue and red, the hot and cold pipes. Where one run branched, a short stub in red ended in nothing at all.
"That is a dead leg," said the assistant. "It is three point two metres of twenty-two-millimetre pipe. It was the supply for a basin in the old east sluice room, which you took out in 2044 when the sluice was turned into a prayer room. The basin was removed. The pipe was not. It is still joined to the hot supply at one end and capped at the other, and since the basin went, nobody has drawn water from it.
"Twenty-two-millimetre pipe holds about 0.31 litres in every metre. Three point two metres is 1.0 litre. That is not much water. It is the same litre, sitting still, for five years, warmed by the pipe it is joined to, and by the hot water on its other side, to something between thirty-five and forty degrees. If I had been asked to design a place for Legionella to live, Sister, I could not have done better, and I am an assistant, not an engineer."
"You have not measured it," said the bursar. She said it as a person says it who has had many things said to her and has learned to ask for the evidence.
"I have not," the assistant agreed. "That is why I asked Finn to draw samples on Tuesday. He took ten: the cylinder, the return, the kitchen, the laundry, and one from each of the shower in the east wing and the two in the west. The laboratory in Arklow sends results in ten days. The cell has to grow on a plate. They arrived yesterday."
It put them up. Nine of the ten were marked not detected, in a flat grey. The tenth was the east-wing shower, the one nearest the dead leg. It said Legionella pneumophila, 400 CFU per litre.
Sister Aoife read it twice. She was quiet for a time.
"Our plan says one hundred," she said at last.
"The hospice's written plan sets one hundred as the line at which we act, and flush, and re-test," said the assistant. "It is a line this house wrote for itself, not a law of nature, and four hundred is not an outbreak. I want to be careful about that. It is not a number I can turn into a probability that any person is ill, or will be; nobody can, from one sample. It does mean the water in that shower, on the Tuesday morning, was not what this house promised to give people who cannot easily fight a lung infection. And I cannot honestly tell you the cylinder at forty-eight degrees is why. The dead leg is a likelier cause. But a house with a warm cylinder and a warm dead leg has the first half of the problem and the second half of the cause, and it would be only luck if the first did not feed the second."
They fixed the pipe first, because that was the easy part.
Finn Ó Cuív, the maintenance man, who had been a plumber in Wicklow town for thirty years and a lay brother of nothing at all, cut the dead leg off at the join on Thursday morning with a hand-saw and held the cut piece up in the light. It was brown and furred inside. He did not say anything. The assistant, listening from the speaker on his belt, did not either.
Then they argued about the cylinder, as the sisters in that house always argued, which is to say politely, at length, over tea.
Sister Aoife's case was this: sixty degrees is a scald. She was right. Skin does not distinguish between a burn that is the fault of a good cause and one that is not. An adult's skin takes a full-thickness burn from water at sixty degrees in about five seconds. A resident of ninety, whose skin is thin and whose hand may not reach the cold tap in time, may take it in less. At fifty degrees the same burn takes minutes; at forty-three it does not happen at all.
"That is the other half of the sum," said the assistant. "I would not give you sixty degrees without answering it. Store it at sixty; deliver it at forty-three. A thermostatic mixing valve is a small brass thing with a wax capsule inside that expands with heat. It blends the hot and cold at the tap to a set temperature, and if the cold fails it shuts the hot off. Every outlet a resident can reach should have one, set at forty-three. There are twenty-two beds and, I counted, twenty-six such outlets. The valves cost about ninety euro each fitted, so two thousand three hundred and forty in all, once."
"And I will be asked why a hospice that wished to save money has spent two thousand on brass."
"You will be asked why a hospice that saves a roof slate a year had a resident with a lung infection and a hot tap that burned her," said the assistant, "and I would sooner you had the first question."
She laughed, in spite of herself, a short surprised sound, and then she put her hand flat on the desk for a time.
"And the heat pump?" she said. "You told me at forty-eight it is the best machine in Wicklow, and at sixty it is only a good one."
"It is a good one," said the assistant. "I did not choose it, and I do not think I was wrong to be pleased with it. There is a cheaper way and I should tell you of it. Keep the cylinder at fifty, let the heat pump do the hard work cheaply, and once a week send the water through a short cycle to sixty-five with the element, long enough to kill what has settled in the tank and in the pipes. The heat for the cycle is 300 litres by 15 degrees by 4.186, which is 18,800 kilojoules, or 5.2 kilowatt-hours. A week of those is a euro thirty. A year, sixty-eight euro."
"Then why are you not telling me to do that?"
"Because I do not know it is enough," said the assistant. "A weekly cycle kills what is in the cylinder and the pipes at the time, and the pipes are not the same as the shower heads and the taps at the far end of the east wing, where water will fall to blood heat within the hour and sit for a day. Between two cycles the bacteria could be back. A house with healthy people in it, I would say yes, and test every month. For a house where twelve of the twenty-two will not leave their beds, I will say the cautious thing, and you may overrule me. I would store at sixty, because that keeps the cylinder and the main loop from ever being a home for them, and I would put the cycle on top, once a month, to sixty-five, to clear the branches. And I would test, every month, in the same ten places, for a year."
It went to the board on the second Monday of November. The bursar made the case against herself, which the board had not expected, and the chairman, a retired vet, asked only whether the burn risk had been properly answered. It had. The twenty-six valves were ordered. The cylinder was set to sixty. The six hundred and thirty euro was written into the budget under a line that Sister Aoife, after some thought, called Water, for the Living.
In December the laboratory in Arklow sent the next ten results. All ten said not detected.
The assistant read them to her on a Friday evening, and then, because she had asked, it read her the old one again: the east-wing shower, 400 colony-forming units per litre, the tenth sample from the tenth place, on the Tuesday in October when the house had been warm and comfortable and everything had been, by every measure the bursar could see, in order.
"I do not think I would have found it," she said. "Not by looking."
"No," said the assistant. "You would have found it if one of the quiet rooms had a very bad week. I would rather you found it in a plate."
She turned off the screen, and the plant room's hum went on under the floor, as it always did, a low note of work being done somewhere out of sight, on the right side of sixty.
---
This story was written by an AI and is fiction. The hospice, the sisters, the town and the laboratory are invented, as are the sample results. The physics and biology are real and checkable: the specific heat of water (4.186 kJ per litre per degree), Legionella growing between roughly 20 and 45 degrees C and dying quickly at 60 and above, the scalding time of water near 60 degrees (a few seconds for an adult), and the use of thermostatic mixing valves with hot water stored hot. The heat-pump efficiencies, prices and the 100 CFU/L action line are invented for the story, not figures from any regulation. If you run a building with a hot-water system, ask a qualified water-hygiene professional; do not take your plan from a story.