Point Two
A parish hall has been made so airtight that it changes its air once in five hours instead of once an hour, and the old gas heater now has nowhere to send what it cannot burn. The hall's assistant cannot say what is wrong with the heater, only what the alarm's one reading means: about eight and a half grams of carbon monoxide an hour, whichever way the leakage test is read. The caretaker who fought for the grant wants to be wrong.
Dougal Reid had been caretaker of the hall at Tom na Croise for thirty-one years, and for the last two of them he had been fighting for it with a grant form.
The hall was a tin-roofed, stone-walled box twelve metres by ten, with a ceiling at two and a half, built in 1931 by men who had been paid in whisky and plain gratitude. It had a gas heater on the north wall that was older than Dougal, and a reputation that the whole glen shared: it was a cold place to be warm in. The wind came through the doors, through the windows, through the gap under the stage, and through a hole where a stove pipe had once been, and on a Thursday in January the soup-and-whist went on beneath a roof that hummed.
Then the grant came. Dougal had written eleven pages for it. Sealed windows, a membrane in the roof, tape on every seam and a draught-proofed door; an airtightness test before, an airtightness test after. The contractor's man had put a great fan in the doorway and pulled the hall to fifty pascals, and written the numbers on a sheet. Before: twenty air changes an hour, at that pressure. After: four.
"Five times tighter," Dougal had said, to the parish council, with his cap in his hands. "Five. We will heat the hall for a fifth of what we paid. Ye'll not know the place."
They did not. By the second week of January the soup-and-whist was warm enough that old Mrs Gillies took her cardigan off, and Dougal stood at the back by the kitchen hatch and let himself be happy.
The assistant in the hall did not have a name either, in the way of the glen, which called most things the thing. It was a small box in the kitchen with a speaker and a screen, put there by the grant as a "monitoring package", and it read the energy meter, the two temperature probes, and a carbon monoxide alarm the council insisted on in every public building since an incident in Aberdeen. It had been quiet for two months. On the second Friday in January, at ten past nine in the morning, it asked Dougal whether he had five minutes.
"I have a reading I do not like," it said. "I would like you to look at the alarm, if you will. Press the button on the front twice."
Dougal pressed. The little screen under the white plastic said PEAK 41 ppm. He frowned at it.
"That's no a lot," he said. "It's no gone off. Fifty's where it goes off."
"That is the first of the two things I would like to say," said the assistant. "The alarm did not sound, and it was right not to, by the standard it was built to. A household carbon monoxide alarm is made to stay silent below thirty parts per million for two hours, and to sound at fifty only after about an hour. It is built to avoid false alarms in a kitchen, not to tell you what a hall full of old people is breathing. Forty-one parts per million, reached at the end of an evening of soup and whist, is not an alarm. It is a number. Would you like me to say what I think it is the number of?"
"Aye," said Dougal. He sat down on a stacking chair.
"Carbon monoxide has no smell and no colour," said the assistant. "A flame makes a little of it whenever the fuel does not get quite enough air or the flue does not quite carry the burnt gas away. A healthy heater makes so little that it does not matter. A heater with a blocked or cracked flue, or a burner out of adjustment, can make a great deal. Where it goes afterwards depends on one thing: how fast the room's air is changed.
"Forty-one parts per million, at the temperatures of this hall, is about forty-seven milligrams in each cubic metre of air. The World Health Organization's guideline for an hour is thirty-five milligrams a cubic metre, and for fifteen minutes, a hundred. Forty-seven is above the hour figure. It is not in the range that would make a healthy adult fall over. It is the range where people with heart disease get chest pain sooner than they should, and where people say, in the car on the way home, that the room gave them a headache, and nobody thinks anything of it, because it was Thursday and they had had two cups of strong tea.
"I want to be plain about what I do not know. I do not know what is wrong with the heater. I have not looked at it. I do not know that anything is wrong with it. What I can do is a sum, and the sum tells me how much it would have to be making, if the alarm is right."
"Go on," said Dougal.
"The hall is three hundred cubic metres," said the assistant. "Before the work, the test said twenty air changes an hour at fifty pascals. In ordinary weather that works out to about one air change an hour, because the rule of thumb is to divide by twenty. That means the old hall swapped all its air for new in an hour, and three hundred cubic metres an hour went out through the walls, whether you liked it or not.
"After the work the test says four, and four divided by twenty is two-tenths of an air change an hour, which is the air changing once in five hours, or sixty cubic metres an hour. That is the figure the whole grant was for.
"Now take a heater that puts out the same gas every hour, and a room that loses some of its air every hour. The concentration climbs toward a ceiling and gets there slowly. The ceiling is the rate the gas goes in, divided by the rate the air goes out. The time it takes to get most of the way is the inverse of the air change rate: one hour in the old hall, five in the new one. After time t the level is the ceiling times one minus e to the power of minus the air change rate times t."
"I'm a joiner," said Dougal. "No a mathematician."
"You are the man who read eleven pages of grant rules," said the assistant, "and I will say it more plainly. In the old hall, a heater that made the same carbon monoxide as it makes tonight would have climbed to a ceiling in an hour or two and stopped there, because the draughts were taking it away as fast as it came. In the new hall, the ceiling is five times higher, and it takes five hours to get there. A two-hour whist drive stops just short of the top. So the alarm read forty-one, which is where you would be at two hours, not where you would stay.
"Working back from forty-seven milligrams after two hours, with the hall's air changing at two-tenths an hour, the ceiling is about a hundred and forty-three milligrams a cubic metre, and the heater is putting in about eight and a half grams of carbon monoxide an hour. The grant's test could be off. The real air change rate could be as low as 0.15 or as high as 0.3, and I tried both. The answer moves between 8.2 grams an hour and 9.4. It hardly moves at all, because the alarm has already told me the product of the two, and I only need to know how it splits."
"Eight grams an hour," said Dougal slowly, "is that a lot?"
"A properly working gas heater of that size is a small fraction of a gram in the same time," said the assistant. "I would call eight and a half grams a heater that needs a gas engineer before it is lit again. I would call it a good deal more than that for a hall that now keeps what it is given."
He sat there a long time, in the grey light from the new windows.
"It was me wanted the tape on the seams," he said.
"It was," said the assistant. "And it was the right thing to want. The heater has probably been making this much for years. The old hall carried it away at three hundred cubic metres an hour, and the level in it could never rise above thirty-three milligrams, which is under the hour guideline. The grant did not make the heater faulty. It took away the one thing that was hiding the fault, and nobody had written that on the form."
Dougal made a noise that was not quite a laugh. "I'll tell the council the grant has worked. It's found the thing the heater was doing."
"I would not say it to the council in those words," said the assistant. "I would say, the new hall gives us a clear reading we could not get in the old one. That is true, and it is kind to you."
He nodded. Then, after a bit, he said the thing that he had been not saying: "Sunday. We've Mass in here Sunday."
The church at Chapeltown had its roof off for the slaters, and the parish had been saying Mass in the hall since December. Eighty people on a cold Sunday morning, an old priest, and a heater that, in a hall that tight, had a much longer day ahead of it than a whist drive.
"Yes," said the assistant. "I have run it. A Mass with the hall opened an hour early to warm and a sermon that goes long is three hours. At the same rate of eight and a half grams an hour, the level at three hours is about sixty-four milligrams a cubic metre, which is fifty-six parts per million. It is above the alarm's own threshold for long enough to ring it at some point in the last hour, but not to ring it for sure, and I would not like the whole matter to depend on whether the alarm happens to be having a good morning. I recommend that the heater is not lit on Sunday. I cannot promise that is the only thing that would fix it. I can tell you that of the things in my reach, it is the only one that does not depend on being sure."
The hall had no other heat. That was the real difficulty, and the assistant did not pretend that it was not.
"There are two electric fan heaters in the school store," Dougal said, "and the council oil-filled radiators in the Tomintoul office. The school keeps them for the nativity. I'd have to ask the head."
"I have costed them," said the assistant. "Four two-kilowatt units on the hall's own supply will warm eighty people against a January morning for an extra eight pounds of electricity. It is not a good bill. It is a bill, not a risk, and it ends. I have also looked at the permanent fix, which is not mine to choose. A gas engineer can test the flue gas and tell you whether it is the flue or the burner; a hall this tight needs a purpose-made vent in any case, to a design someone who is qualified draws up. I have asked the grant's contractor for the name of one. The parish will pay for the engineer. I think the grant officer may be glad to hear why."
"And the Thursday whist?"
"You may hold it," said the assistant. "With the doors opened for ten minutes each half hour, which will cost you the warmth you meant to keep, and with the heater off. Or you can move it to the school. That is your decision, and the council's, and I will not make it by moving the number around. Whichever you choose I will keep the log, and I will say the alarm's own reading aloud on Thursday evening, so that nobody has to ask."
Dougal stood, put his cap back on and took it off again.
"Thirty-one years," he said, "I lit that heater myself."
"And nobody was harmed that I can find," said the assistant, "and I looked, through the minutes of the hall committee back to 2017. Two people said they had a headache after a funeral tea. That is two out of a very large number of funeral teas. I would not call it nothing. I would not call it proof. It is the sort of thing that is only worth writing down once a hall has been made tight enough to see."
The heater was tagged on Friday afternoon with a hand-lettered card that said DO NOT LIGHT. DOUGAL. The oil-filled radiators came in the school van. On Sunday morning the hall was a degree and a half cold at the first bell and eleven degrees warmer at the Gloria, and Father Alasdair, who was eighty-one, preached for eleven minutes and called the radiators the new Pentecost.
The engineer came on Tuesday. A bird had nested in the flue in the spring of 2046, and had not survived the winter; what was left of the nest, with soot, had closed about two-thirds of the opening. He cleared it, fitted a new cowl and a proper vent through the north wall, tested the burner and gave it a certificate. On Wednesday evening, with eighty chairs set out for nobody, the assistant lit it for an hour and read the alarm's peak aloud.
"Two parts per million," it said. "That is where it should be, with the air changing once in five hours, point two of the hall an hour, and nothing in it to add."
"Point two," said Dougal. He wrote the reading on the whiteboard in the kitchen, under the date, and left a space on the line beneath for next week's.
The grant officer, when she came in March, asked him what the board by the hatch was for.
"It's the reading," he said. "We take it every Thursday. Whoever's on the soup writes it down."
"Is it required?"
"No," said Dougal. "But it's a tight hall. It would be a poor thing to be warm in a place and not know why."
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This story was written by an AI and is fiction. The hall, the glen, the parish, the priest, the engineer and the grant are invented. The sums are real and can be checked: carbon monoxide at 1 ppm is about 1.145 mg per cubic metre at room temperature; a room's concentration approaches generation divided by ventilation as one minus e to the power of minus the air change rate times time; the 50-pascal test divided by about 20 is a common rough guide to natural air changes; the guideline values of 35 mg per cubic metre for an hour and 100 for 15 minutes are the World Health Organization's. The standard household alarm is built not to sound under 30 ppm within two hours, which is why it can stay silent in a room that is already above the hour guideline. The emission rates, the leakage figures and the glen's history are invented for the story. If you use gas or solid fuel appliances in a building you have made more airtight, have them checked by a registered engineer and fit a certified alarm; do not take your plan from a story.