HVAC control solutions for heating and ventilation

HVAC: ventilation, heating and indoor climate control

We always have a solution for fresh air.

Fans, ducting, dampers, filters, decentralised heat recovery units, CO2 and air quality sensors, control automation, air conditioners, air purifiers and dehumidifiers – for homes, offices and commercial projects. Below the product list you will find a selection guide with diagrams.

Fans Ducts and fittings Dampers Silencers Air filters Trickle vents Diffusers Cowls HVAC automation Electric heating Air conditioners Air purifiers Dehumidifiers Aroma diffusers

Stuffy air, condensation on windows, mould? A fan with humidity control, a CO2 sensor or a decentralised heat recovery unit – see what to choose or ask us.

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HVAC guide: fresh air at home, in the office and on site

Here you will find a quick choice by situation, what really determines air quality, how to read sensor values, how much air different rooms need, the most common mistakes with diagrams, and answers to the key questions. More detailed selection advice is given in each subcategory description.

Colour key: ■ information · ■ benefit, solution · ■ ⚠ check · ■ ⚡ safety, mistakes

Contents: What do you need? · Sensors and automation · What we breathe · Insulated house · Sensor readings · How much air is needed · What to check · Mistakes · Diagrams · FAQ

What do you need? Quick selection

Situation	Solution	Where to look
You have insulated the house or replaced the windows – the air is stuffy, windows mist up	Decentralised heat recovery units (installed in pairs through the wall, no ducting) or a central MVHR system	Insulated house, Fans
Condensation on windows, mould in the bathroom or kitchen	Extract fan (with timer or humidity sensor) + air supply through a trickle vent	Fans, Trickle vents
Damp basement, storeroom, construction site	Dehumidifier sized for the floor area and humidity level	Dehumidifiers
Stuffy office, server room or flat in summer	Portable air conditioner – no fixed installation	Air conditioners
Dust, allergens, odours	Air purifier with HEPA / carbon filter; in a ventilation system – an in-line duct filter	Air purifiers, Filters
Supplementary or backup heating needed	Electric heater with thermostat	Electric heating
Ventilation of a production or storage area	In-line or centrifugal fan, duct run, dampers, filter, speed controller	Ducts, Dampers
Noisy existing system	Duct silencer + fan speed control	Silencers
After renovation: dust, paint and adhesive odours	Air quality sensor measuring PM2.5 / PM10 and TVOC / HCHO + air purifier with HEPA and activated carbon filter + more intensive ventilation	Sensors, Air purifiers
Ventilating through windows facing the street, smoke from chimneys noticeable	A PM2.5 sensor shows when it is better to close the window; as a long-term solution – mechanical air supply through an ePM1 (F7) filter	Sensors, Filters
You want automatic control based on CO2, humidity or temperature	Sensor + controller / speed controller, damper actuators	HVAC automation

Want truly clean air? Let sensors control the climate

A manually switched fan usually runs at the wrong time. We offer fans with humidity control – they switch on by themselves after a shower and switch off when humidity drops – and CO2 sensors, which increase or reduce ventilation according to the actual air quality. After renovation or when ventilating through windows facing the street, use combined air quality sensors – in addition to CO2 they also measure particulate matter PM2.5 / PM10. The result: fresh air at all times, less moisture and mould, and the fan does not run unnecessarily or waste heat.

Bathroom, utility room: fan with humidity sensor and timer.
Office, classroom, bedroom: CO2 sensor + speed controller or EC fan (0–10 V).
Insulated house, new windows: decentralised heat recovery units – fresh air with heat recovery, no ducting.
After renovation, near a busy street: CO2 + PM2.5 / PM10 (and TVOC) sensor together with an air purifier or filtered air supply.
Smart home: CO2, temperature and humidity sensors with smartphone control and automation scenes.

Fans · CO2 sensors and HVAC automation · Smart CO2 / humidity sensors · How to read sensor values · How it works – diagram 3

What do we actually breathe?

Every day a person breathes in about 11,000 litres of air, and we spend most of our time indoors – at home, at the office, at school. That is why indoor air quality affects how we feel more than it may seem.

Clean outdoor air – what it consists of

Nitrogen ~78 %

Oxygen ~21 %

The remaining ~1 % – argon, CO2 (~0.04 %, about 420 ppm), water vapour. The air we exhale contains about 4 % CO2 – a hundred times more than outdoors, which is why CO2 rises quickly in an unventilated room.

✗ What we breathe in a poorly ventilated room

CO2 1500–2500 ppm – stuffy, drowsy, poor concentration
Mould spores – can cause allergies and aggravate asthma
House dust mite allergens – mites multiply in a damp environment
TVOC and formaldehyde – from paints, adhesives, furniture
Particulate matter PM2.5 – from cooking, candles, outdoor smog
Excess moisture – above 65 % RH, condensation on windows

✓ What we can breathe with proper ventilation

CO2 up to ~800–1000 ppm – a clear head, better sleep
Humidity 40–60 % – no condensation or mould
Filtered air – less dust, pollen and smog
Vapours and odours removed after cooking or renovation
Heat stays in the home – with heat recovery
Everything is measured – sensors show when to ventilate

Mould is not just a stain on the wall. It is a sign that the room has too much moisture and too little air exchange. Remove the cause – the diagrams show how.

Insulated your house? Don't forget ventilation

When a house is insulated and the windows are replaced, the building becomes airtight – heat stays inside, but so do moisture and CO2. In the past, leaky windows and gaps “exchanged” the air; now ventilation has to do this job.

Insulation, new windows

→

The house becomes airtight

→

Moisture and CO2 stay inside

→

Condensation on windows, mould, stuffy air

→

✓ Solution: heat recovery

Decentralised heat recovery units – ventilation without ducting

A decentralised (single-room) heat recovery unit is installed through an external wall. Inside it there is a ceramic heat accumulator and a reversible fan that changes the airflow direction roughly every minute: the warm extract air heats the ceramic, and the incoming outdoor air is warmed by it. The units are installed in pairs – while one supplies, the other extracts.

Suitable for renovated flats and houses, where there is no room for ducting.
Fresh air with heat recovery – ventilation without open windows or draughts.
Simple installation – a hole in the wall and a 230 V supply.

How it works – diagrams 4 and 5. Look for decentralised heat recovery units in the fans category or ask us – we will size them for your rooms.

How to read air quality sensor values

A sensor shows numbers, but it is not always clear whether they are good or bad. The table gives a simple “traffic light” scale: find your reading and see what to do.

Reading	● Good	● Acceptable	● Ventilate	● Poor
CO2 ppm – is ventilation sufficient	up to 800	800–1000	1000–1400	above 1400
PM2.5 µg/m³ – fine dust, smoke, smog	up to 15	15–25	25–50	above 50
PM10 µg/m³ – coarser dust, pollen	up to 45	45–75	75–100	above 100
TVOC mg/m³ – vapours from paints, adhesives, furniture	up to 0.3	0,3–1	1–3	above 3
HCHO mg/m³ – formaldehyde	up to 0.05	0,05–0,1	—	above 0.1
Humidity RH % – relative humidity	40–60	30–40 / 60–65	above 65	above 70 – risk of mould
What to do?	Nothing – the air is good	Monitor; ventilation in normal mode	Increase ventilation or air the room	Ventilate intensively; if PM is high – close the windows and switch on the purifier

The limits are indicative and intended for household assessment. The green zone limits for PM2.5 and PM10 correspond to the WHO 24-hour guideline values (15 and 45 µg/m³), HCHO – to the WHO 0.1 mg/m³ guideline, TVOC – to the levels of the German Environment Agency (UBA). Some sensors show TVOC in other units (ppb or as an index) – in that case follow the sensor's own scale.

⚠ How to avoid misreading the values:

Look at the trend, not a single number. A short spike while cooking or cleaning is normal. What matters is whether the reading stays high for a long time.
A CO2 sensor does not detect dust or vapours, and a PM sensor does not detect CO2. After renovation and near busy streets, choose a combined sensor.
True CO2 is measured by an NDIR sensor. Cheap “eCO2” readings are only calculated from TVOC and do not show the CO2 level accurately.
Position the sensor correctly: at a height of ~1–1.5 m, not next to a window, door, cooker or radiator, and not directly in people's breathing zone.

How much air is needed: children's room, kitchen, office, assembly hall

Room	Indicative airflow	Example
Children's room, bedroom	25–30 m³/h per person	2 children → 50–60 m³/h
Living room	by number of people, ~25 m³/h per person	4 people → ~100 m³/h
Kitchen (extract)	50–75 m³/h; when cooking – cooker hood	~75 m³/h
Bathroom / shower	25–50 m³/h	~50 m³/h
WC	20–25 m³/h	~25 m³/h
Office	25–36 m³/h per person	6 employees → 150–220 m³/h
Classroom, training room	25–30 m³/h per person	25 pupils → 625–750 m³/h
Assembly or conference hall	20–30 m³/h per person	150 seats → 3000–4500 m³/h

The bars show the example values on a compressed scale so that both small and large rooms remain visible.

How to calculate: number of people × airflow per person. E.g. an assembly hall with 150 seats × 25 m³/h = 3750 m³/h. An airflow like this calls for an engineered system with a heat recovery unit – a single domestic fan will not do the job. A children's room for 2 children needs ~50–60 m³/h – a pair of decentralised heat recovery units or a trickle vent with extract can provide this.

⚠ What to check before buying

KibirkštisBefore buying, I always check these points – it saves both money and a second trip to site.

What to check	Why it matters
Airflow and pressure	Whether the fan will deliver the required m³/h against the real resistance of the duct run – not just the catalogue maximum.
Diameter	Whether the fan, ducts, dampers and silencer share the same nominal diameter (Ø100, Ø125, Ø160…).
Power supply and control	230 V or 24 V; ON/OFF, 3-point or 0–10 V; whether this is compatible with your controller or distribution board.
Installation location	For damp rooms – a suitable IP rating (in a bathroom usually IPX4 or higher); outdoors – protection against rain and snow.
Sensors	True NDIR CO2, not “eCO2”; whether it measures PM2.5 / PM10; output – relay, 0–10 V or Wi-Fi / Zigbee.
Boiler, fireplace, gas cooker	If fuel is burned in the room – provide a make-up air opening and a CO detector.
Heat loss	For continuous ventilation in an insulated house, heat recovery is worth choosing – the heat is returned.

✗ Most common mistakes

Mistake	Consequence
The fan is chosen by its catalogue maximum	In a real duct run the airflow is much lower – the room remains unventilated.
No air supply (trickle vent, gap under the door)	The extract fan “pulls against nothing” – moisture stays, mould appears.
The house is insulated, but ventilation is forgotten	Stuffy air, condensation on windows, mould in the corners.
Duct diameter reduced	More noise, less air.
No backdraft damper	When the fan is off, cold air and odours flow back.
Uninsulated duct in a cold loft	Condensate drips onto the ceiling and into the fan.
Mismatched control (24 V actuator on 230 V, 0–10 V signal to an ON/OFF input)	Damaged actuator or control does not work.
Filters not replaced	Airflow drops, the fan motor overheats.
Powerful extract in a house with a boiler or fireplace and no make-up air	⚡ The chimney draught may reverse – risk of CO poisoning.

What the key mistakes look like in practice – see the diagrams.

⚡ Safe installation – advice from Fazė

Fans, electric heaters and actuators are connected via suitably rated protective devices in accordance with the manufacturer's instructions.
Circuits in bathrooms and other damp rooms – with 30 mA residual current protection (RCD); the IP rating of the device must match the installation zone.
In rooms with a boiler, fireplace or gas cooker – a make-up air opening and a CO detector.
Connection to the 230 V / 400 V mains must be carried out by a qualified electrician.

☝ Elsprendimai.eu recommends: to control and protect the ventilation system, add contactors and relays, motor protection devices, CO2, temperature and humidity sensors, SONOFF controllers and enclosure heaters for distribution boards installed in unheated rooms.

Diagrams: how it often is and how it should be

In each diagram, the most common mistake is on the left and the correct solution on the right. The numbers in the diagram correspond to the explanations below it.

Diagram 1. Air supply and mould. An extract fan without an air supply does not remove moisture. The trickle vent, the gap under the door and the bathroom extract must work as one chain.

KibirkštisThe bathroom fan is running, but the windows still mist up. Why?

FazėBecause the air has nowhere to come from. Let it in through a trickle vent, leave a gap under the door – then the extract will really work.