Guides · Air · 13 min read · Updated September 2026

The air in the house

Qi was breath before it was anything else, and the tradition’s word for a closed room was dead. What the manuals meant by living and dead qi; where the air stops in a flat, the room with one window and the bathroom with none; the two numbers a monitor gives, carbon dioxide and fine particles, and where the research sets the lines; the stove, the candle and the incense as the house’s own smoke; the plants that do not clean the air; and the morning window the tradition opened before it did anything else.

Oriented E 090°

Wood

Fig. 01 A window open onto trees. The tradition opened the windows in the morning before it did anything else, and called what came in living qi.

The word at the centre of feng shui means breath, and the qi essay follows it through the philosophers and the physicians; this guide follows it through the window. The tradition called the air of a moving house living qi and the air of a closed room dead, opened its windows in the morning before it did anything else, and disliked a room with an opening on one side only and a room with none. A monitor now gives the same judgement in two numbers, and the research says where the lines fall. This guide gives the tradition’s rules for air, the rooms where it stops, the numbers, the smoke a house makes for itself, and the plants that do not help.

Living qi and dead

The Book of Burial says that qi rides the wind and scatters, and the yang-house manuals, applying the sentence to a room, drew two conclusions from it that look contradictory and are not: a house must be sheltered from wind, and a house must not be closed. The sheltered house holds its qi; the closed house kills it, and the manuals’ word for the air of a shut room, a windowless closet or a bathroom without an opening is dead qi, si qi, or turbid, zhuo qi, as against the living qi, sheng qi, of a room the morning has passed through. Knapp records the household habit that follows: the windows and the doors opened at first light, the house aired while the bedding is turned and the floors swept, and closed again against the heat or the cold, a rhythm the house through the year essay places in the calendar. The rule that a room should have its window on the side the breeze comes from and its door on the other, so that the air crosses it, is the same rule the windows guide draws as cross-ventilation, and the tradition’s dislike of the through-hall fault, a straight line of openings from the front of the house to the back, is a dislike of a draught, not of air: the manuals want the air to move and to be slowed, which is what a turn in the plan does.

Where the air stops

Plan 01 Where the air stops A flat of ten metres by six and a half with windows on its north and south walls and none on the east or west. Air moves through it when a window on one side and a window on the other are open with the doors between them, and the arrows draw that path, from the living room’s south window through the hall to the bedroom’s north window; it is the tradition’s qi moving through the house and the engineer’s cross-ventilation, and it changes the air of the flat in minutes. The rooms shaded are the ones where it stops: the second bedroom, with a window on one wall only, where air comes in and goes out by the same opening and the room’s far corner is never reached; and the internal bathroom, with no window at all, which the tradition read as the house’s one dead room and the guide gives an extractor. The small marks on the doors are undercuts and the marks on the window frames are trickle vents, which let the air move at night with everything shut.

Air moves through a house when it has somewhere to go, and the drawing above shows where it does not. A flat with windows on two sides changes its air in minutes when one on each side is open with the doors between them, and the arrows draw the path, from the living room’s window through the hall to the bedroom’s: this is the tradition’s qi moving through the house and the engineer’s cross-ventilation, and the windows guide gives the physics for one room. The rooms shaded are the ones the tradition called dead. The bedroom with a window on one wall only takes air in and lets it out by the same opening, and its far corner is never reached, which is where the damp shows first and where the World Health Organization’s guidance on damp and mould, which the bathroom page cites, finds the health effects. The internal bathroom with no window at all is the flat’s one truly dead room, and the manuals that had no bathrooms would have refused it; the guide gives it an extractor that runs on a timer, a door with an undercut, and a habit of leaving the door open when the room is empty. The small marks on the drawing are the joiner’s answers for the night, when everything is shut: undercuts on the doors so that the rooms breathe into one another, and trickle vents in the window frames so that the flat breathes at all.

Design observation · The house’s own smoke

The tradition’s house made its own bad air, and so does the modern one. The stove is the first source: a gas hob without an extractor puts nitrogen dioxide into a kitchen at levels the World Health Organization’s indoor guidelines set limits for, and frying with the hood off sends fine particles through the flat; the kitchen page’s extractor is an air rule before it is a fire rule. Candles and the fireplace, which the fire guide gives their places, are the second. Incense is the third and the one the tradition would not expect: Lin and colleagues’ review finds an incense stick in a small closed room producing particle levels above those of a busy street, and the households that burn it daily before the altar showing the airway effects. The altar’s incense is kept, since it is the tradition’s, and the window near the altar is opened while it burns, which the households of the coast do already.

Two numbers

Fig. 02 The air in a room in two numbers. Above, carbon dioxide in parts per million, which is the measure of how much of the room’s air has been breathed already: outdoor air at about four hundred and twenty, a ventilated room at eight hundred, a meeting room by noon at fifteen hundred, a closed bedroom by morning at two and a half thousand and more with two sleepers. Allen and colleagues found decision-making measurably slower at a thousand and worse at fourteen hundred, which is where the mark is set. Below, fine particles in micrograms per cubic metre, on a scale that doubles every step: a clean room at five, the World Health Organization’s daily guideline at fifteen, a city street at forty, frying with the hood off at a hundred, an incense stick in a small room at two hundred and fifty and a candle-lit dinner beyond it. The tradition’s stale qi is the first scale and its smoke is the second, and both are the reading of a window that has not been opened. The carbon dioxide figures are typical, from the indoor-air literature and Seppänen’s review; the particle figures are typical peaks from the same literature and from the incense studies, and fall within an hour of the window opening. A monitor for both costs less than a practitioner’s visit.

A room’s air can now be read from a device that costs less than a consultation, and the drawing above gives the two numbers it reports and where the lines fall. Carbon dioxide, in parts per million, is the measure of how much of the room’s air has been breathed already: outdoor air sits at about four hundred and twenty, a ventilated room at eight hundred, a meeting room by noon at fifteen hundred, a closed bedroom by morning at two and a half thousand and more with two sleepers. Seppänen, Fisk and Mendell’s review of the buildings research fixed a thousand as the line above which symptoms, absence and complaints about the air rise, and Allen and colleagues found decision-making measurably slower at a thousand and worse at fourteen hundred in an office whose occupants did not know the air had been changed. Fine particles, in micrograms per cubic metre, are the smoke: a clean room at five, the World Health Organization’s daily guideline at fifteen, a city street at forty, frying with the hood off at a hundred, an incense stick in a small room at two hundred and fifty. The tradition’s dead qi is the first scale and its smoke is the second, and both are the reading of a window that has not been opened. A monitor by the bed, read in the morning, tells a household in a week what the manuals told it in a word.

The night, measured

Fig. 03 A bedroom’s night in carbon dioxide, for two sleepers from eleven until seven, drawn from the typical figures of the bedroom-air studies. With the window and the door shut, the room starts near outdoor air at five hundred parts per million and climbs all night, past the thousand where the research puts the first effects by one o’clock, to two and a half thousand by morning, which is the reading Strøm-Tejsen’s sleepers woke to and slept worse for. With trickle vents in the frame or the door left ajar the curve flattens at twelve or thirteen hundred, over the line but not far. With the window open a hand’s width it stays near eight hundred, the ventilated room of the guide’s scale. At seven the morning window is opened, and the shut room falls from its peak to outdoor air in a quarter of an hour, which is the tradition’s first rule of the day drawn as a line. A monitor on the bedside table draws this curve for any household in a week, and the household then knows which of the three lines it sleeps under. The figures are typical of the studies of two-person bedrooms; a small room, a large sleeper or a child in the bed moves the shut curve up. Strøm-Tejsen and colleagues measured about two thousand four hundred parts per million closed against eight hundred open, and better sleep and next-day scores with the window open.

The two numbers above are read once; the drawing here reads the first of them all night, and it is the curve the tradition’s morning rule was written for. A bedroom with two sleepers and the window and door shut starts the night near outdoor air, five hundred parts per million, and climbs without a pause: past a thousand, where the research puts the first effects on judgement and sleep, by one o’clock, and to two and a half thousand by morning, which is the reading Strøm-Tejsen and colleagues measured in the bedrooms of students who slept with the window closed and found sleeping worse and concentrating worse the next day than the same students with it open. The two other lines on the drawing are the joiner’s and the household’s answers. Trickle vents in the window frame, or the bedroom door left ajar onto a hall with a window, flatten the curve at twelve or thirteen hundred, over the line but not far over it, and the windows guide gives the vents; the window open a hand’s width, which the quiet guide says costs the street’s noise and the sleep guide says costs the dark if it costs the curtain, holds the room near eight hundred all night, which is the ventilated room of the scale above. At seven the shut room’s curve falls from its peak to outdoor air in a quarter of an hour when the window is opened, and the fall is the tradition’s first rule of the day drawn as a line: the households that opened every window at first light were bringing a room of two and a half thousand back to five hundred before they swept it, and did so for centuries without a number. A monitor on the bedside table, which costs less than a practitioner’s visit and less than a lamp, draws this curve for any household in a week, and the household then knows which of the three lines it sleeps under and what the morning window is worth to it, in parts per million.

Air, in order

The morning window. Every room opened at first light, the bedding over the sill, for the time it takes to sweep; the tradition’s first rule of the day.
Two sides, and the doors between. A window on one side, a window on the other, the doors open; the air crosses the flat in minutes.
The dead rooms found. The one-window room’s far corner, the windowless bathroom, the cupboard; an extractor on a timer, undercuts, trickle vents.
The smoke caught. The hood on when the stove is, the candles on the table, the incense with a window open beside it.
The numbers read. A monitor by the bed: under a thousand parts per million by morning is the ventilation doing its work. Fine particles are read against the World Health Organization’s fifteen micrograms averaged over a day, not against a morning’s figure, and opening a window lowers them only when the air outside is cleaner than the air in the room.
The plants for the view. Keep them for what they do; the air is the window’s.