Indoor Air Quality (IAQ)

What is indoor air quality (IAQ)?

Indoor air quality, or kvalita vnútorného vzduchu, describes how healthy and comfortable the air inside a building is for the people living in it. It depends on the pollutants released inside the home, the moisture in the air and on surfaces, and how much fresh outdoor air reaches each room. In an airtight family house the envelope keeps indoor pollutants in as well as weather out, so the air needs deliberate management.

Which pollutants matter most in a family house?

Most indoor pollution comes from a few sources present every day. The table sorts them by origin, behaviour and control lever.

Pollutant or factor	Main source in a family house	How it behaves indoors	Main lever
Carbon dioxide (CO2)	Occupants breathing, most of all in bedrooms and living rooms at night	Builds up steadily when rooms stay closed	Ventilation rate
Water vapour (humidity)	Showers, cooking, drying laundry, plants, occupants	Condenses on cold surfaces and feeds mould	Extraction at source, ventilation, heating
Volatile organic compounds (VOCs)	Paints, adhesives, flooring, furniture, cleaning products	Strongest when materials are new, then falls off gradually	Material choice, ventilation
Radon	Soil gas entering through the ground-contact floor	Accumulates in rooms in contact with the ground, such as cellars and ground floors	Radon barrier and protective measures under the slab
Fine particles	Wood stoves, fireplaces, frying, candles	Spreads through the house and settles on surfaces	Sealed combustion, extraction, source control

How does CO2 from occupants affect indoor air?

Every person exhales carbon dioxide, so CO2 is the simplest indicator of whether ventilation is keeping pace with the people in a room. It rises fastest in bedrooms overnight with the door closed, which is the usual reason an occupied room feels stuffy. CO2 matters more as a marker than as a hazard in itself. Measurement and design use are covered in indoor CO2 concentration.

Why do humidity and mould matter for air quality?

Excess water vapour is not a pollutant in itself, but it changes everything else. When humid air meets a cold surface, such as a window reveal or a cold corner at a thermal bridge, it condenses and feeds mould growth, known in Slovak as plesne. Families usually spot it first in bathrooms, behind furniture on external walls and in window corners. Control means removing moisture where it is produced, ventilating, and keeping interior surfaces warm.

How do VOCs from finishes and furniture build up?

Volatile organic compounds, or prchavé organické zlúčeniny (VOC), are gases released by many building and household products. The main sources are solvent-based paints and varnishes, adhesives, flooring, board materials, new furniture, carpets and cleaning products. Emissions peak when a product is new and after a renovation, so a freshly finished house can smell strongly for a while. Low-emission materials chosen at the design stage cut the load at source, and ventilation dilutes what remains.

Why is radon from the ground a concern?

Radón is a naturally occurring radioactive gas from rock and soil. It enters through cracks and service penetrations in the ground-contact floor. It is odourless and colourless, and its level depends on local geology, so neighbouring plots can differ. The risk is established during site investigation through a radon survey. Where levels are elevated, the design adds a radon barrier and protective measures under the slab, and ventilation dilutes whatever gas still gets in.

How do wood stoves and cooking add fine particles?

Fine particles are tiny solid or liquid particles small enough to reach deep into the lungs. In a Slovak family house the main sources are kachle and krby burning wood, frying and grilling, and candles. A well-operated stove burning dry wood releases less than a smouldering one. Cooking particles are cleared best by a cooker hood (digestor) that exhausts outside, because a recirculating hood only filters grease.

How is indoor air quality different from indoor CO2 concentration?

Indoor air quality is the whole picture, while CO2 concentration is one measurable part of it. CO2 is easy to measure and tracks occupant-generated air, so it serves as a proxy. It does not reveal radon, VOCs or fine particles.

Aspect	Indoor air quality (IAQ)	Indoor CO2 concentration
What it describes	The overall condition of the air, from many pollutants and moisture	One gas, produced mainly by people
Typical measurement	A range of sensors and tests, some needing laboratory analysis	A simple sensor, widely available
Role in design	Sets the overall ventilation and source-control strategy	Helps set and check how ventilation responds to occupancy
Blind spots	Hard to reduce to a single reading	Does not show radon, VOCs or fine particles

Which levers improve indoor air quality the most?

Three levers do most of the work. Ventilation dilutes and removes what is produced inside, source control stops pollutants at entry, and sealed combustion keeps combustion gases out of the living space. Ventilation is usually the starting point because it affects CO2, moisture and odour together.

Ventilation

In an airtight house, opening windows is not a reliable source of fresh air, so a controlled system supplies it continuously. A heat recovery ventilation unit does this while reclaiming heat from the extracted air. Where occupancy varies, demand-controlled ventilation adjusts airflow to the measured load.

Source control

Choosing low-emission paints, adhesives, boards and furniture, and capturing cooking moisture and particles at the hob, reduces the load before ventilation has to deal with it.

Sealed combustion

A room-sealed appliance takes combustion air from outside and vents its flue outside, so it neither draws on nor discharges into the living space. Open-flue appliances in an airtight house can spill combustion gases back into the room, so combustion air is checked during design.

What are common misconceptions about indoor air quality?

The most common misconception is that opening a window solves everything, yet it cannot stop radon rising from the ground. Another is that a fresh smell means clean air, although some VOCs have no noticeable smell. A clean-looking room is not necessarily a healthy one, because moisture and radon leave no visible sign.