Frequently Asked Questions About Air Conditioners and Dehumidifiers

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Air conditioners and dehumidifiers are among the products we get the most inquiries about at atria.sk, from customers who aren't sure themselves what they actually need. Below we have compiled the questions that come to us most often by phone, email, and through discussions directly on the products, and we answer them the way we would answer a neighbour - without unnecessary sales fluff, but also without avoiding unpleasant facts (for example, that an air conditioner in an old, uninsulated panel-building flat will have different parameters than in a new build).

What air conditioner output do I actually need

This is by far the most common question, and also the one where the most mistakes are made - usually towards undersizing. A customer thinks "my room is 20 m², I'll buy a smaller unit and save money", and then in summer finds out the air conditioner runs non-stop at full power and still can't cool the room to the desired temperature.

An approximate calculation that actually works

In practice, a simple rule is most often used: for a standard insulated room in an apartment building, count on a cooling output of approximately 100 W per square metre of floor area with a normal ceiling height of up to 2.7 m. For a new build with good insulation and triple glazing you can go slightly lower; conversely, for a room with large glazed areas facing south or west, an attic room under a metal roof, or a space with computers/kitchen appliances generating heat, you should add a surcharge of 15-30 % to the basic calculation.

In practice this looks like: a unit with a cooling output of around 2.5 kW reliably covers a room up to approx. 25 m², a unit around 3.5 kW handles a room up to approx. 35 m², and the more powerful 5.0 kW variant is suitable for a larger living room or connected living space up to approx. 50 m². These are approximate values for an ordinary Slovak flat or family house, not laboratory figures - for a specific project (for example a glazed office or an attic room) we always recommend consulting an installation company directly, which can carry out an on-site inspection.

Recommended models by output class (Vaillant climaVAIR pro, single split - outdoor and indoor unit with remote control included):

VAIB1-025WN outdoor and indoor unit with remote control - the smaller output variant, suitable for an ordinary bedroom, children's room, or home office up to approx. 25 m². A complete single-split package including remote control, nothing extra to buy besides installation. Price from €527.00.

VAIB1-035WN outdoor and indoor unit with remote control - the mid-power variant, the most versatile choice for an ordinary living room or larger room up to approx. 35 m². The most frequently sold output in this series, precisely because of the balance between price and versatility. Price from €561.00.

VAIB1-050WN outdoor and indoor unit with remote control - the most powerful variant in the series, suitable for a connected living space or larger room up to approx. 50 m², or wherever there is an increased heat load (glazing, south-facing orientation). Price from €833.00.

Air conditioner or dehumidifier - what's the difference and when the cheaper solution is enough

The second most common question goes roughly like this: "Is a dehumidifier enough for me, or do I need an air conditioner outright?" The answer depends on what your real problem is - heat, or humidity.

An air conditioner primarily cools the air (it removes heat and releases it outside via the outdoor unit); it reduces humidity only as a side effect through condensation on the evaporator. A dehumidifier, on the other hand, does not significantly cool or heat the air; its only job is to reduce the relative humidity of the air - in summer as well as in winter, regardless of temperature. So if you are fighting mould in the bathroom, condensation on bedroom windows in winter, or need to dry out a windowless laundry room, a dehumidifier is a cheaper and more energy-efficient solution. If your problem is a high temperature in the room during summer, you need an air conditioner - a dehumidifier will not solve the heat for you.

A common mistake we see in discussions: a customer buys a dehumidifier hoping it will "at least cool a little" an overheated attic room in summer. A dehumidifier actually warms the air slightly (the compressor and motor produce heat that goes back into the room), so in a hot room it tends to make the situation worse rather than better.

When a combination of both makes sense

In practice, a combination works well in households with a basement, or in new builds just after completion, where there is still a lot of residual moisture in the structure - the air conditioner handles summer temperatures in living areas, while a small dehumidifier running in the basement or laundry room protects against mould regardless of the season.

How much will an air conditioner cost to run

This is a question customers often ask only after buying, once a higher electricity bill arrives - yet an approximate calculation isn't complicated. Modern inverter air conditioners (and all units we sell are inverter models) commonly have an energy efficiency ratio (EER) between 3 and 4, which means that for every 1 kW of electrical input they can remove 3 to 4 kW of heat from the room. When cooling a room with a 2.5 kW unit, this means in practice an electrical draw of approximately 0.6-0.8 kW when running at full power - however, with inverter control the unit runs at partial output most of the time, because it is only maintaining the temperature already reached, so the real average consumption over the course of a day is noticeably lower than when running at maximum.

A real-world example: if a 2.5 kW unit runs on a hot summer day effectively for about 6 hours at an average draw of 0.4 kW (a combination of full-power starts and a maintenance mode), consumption for the day works out to approximately 2.4 kWh. At a typical electricity price, that's on the order of a few euros per day of intensive operation, not tens of euros. For a larger 5.0 kW unit and a larger room, the figures scale up proportionally, but the principle stays the same - inverter control is key, and is the reason units without it are almost never sold today.

What increases consumption the most in practice

From specific cases we deal with through discussions and service, the most common causes of unnecessarily high consumption are: a target temperature set too low (a difference of 5 °C from the outdoor temperature is entirely sufficient and noticeable; every additional degree increases consumption disproportionately), open windows or doors during cooling, a dirty air filter (restricts airflow, forcing the unit to work harder), and undersized output relative to the room area - from the point on output above.

Installation and common faults - what to prepare for

Installing a split air conditioner (outdoor + indoor unit connected by refrigerant piping) is not a DIY job - it requires professional handling of refrigerant, evacuating the circuit, and electrical wiring, which should be done by a certified installer. The typical installation price depends on the length of the pipe run and the difficulty of positioning the outdoor unit (balcony, façade, roof), so we always recommend getting a quote from a specific installation company in your region, based on an on-site assessment.

As for common faults, in the vast majority of cases we deal with through customer support, it comes down to one of a few typical situations - and you can check most of them yourself before calling a service technician.

Frozen indoor unit

If frost or ice appears on the indoor unit or on the refrigerant piping, the most common cause is insufficient airflow (clogged filter, unit blocked by furniture or curtains) or operation at too low an outdoor temperature in cooling mode, for which the unit is not designed. In such a case, turn the unit off, let it defrost completely (do not scrape the ice off by force), and check the filter and the free space around the unit.

Outdoor unit is noisy or vibrating

Increased noise or vibration is often caused by an incorrectly mounted bracket for the outdoor unit on the façade, missing rubber dampers, or a dirty fan and condenser (for example pollen, leaves, dust from nearby construction). Regular cleaning of the outdoor unit once a year, ideally in spring before the season, prevents most of these problems.

Dehumidifiers - the most common practical questions

For dehumidifiers we mainly deal with two things: what size (output) model to choose and exactly where in the flat to place it.

What humidity level is fine in a flat

For an ordinary living room, a relative air humidity in the range of 40-60 % is recommended. Below this range the air tends to be unpleasantly dry (irritated mucous membranes, static electricity); above 60 % relative humidity, the risk of condensation on cold spots (room corners, window lintels, corners behind furniture against the outer wall) rises significantly, and with it the risk of mould. A cheap hygrometer is a good first investment even before buying a dehumidifier - it will show you whether the problem actually exists and how big it is.

Where to place a dehumidifier

A dehumidifier should stand freely, at least 15-20 cm from walls and furniture, so it has enough space for air intake and outlet, and in the room with the biggest problem (windowless bathroom, laundry room, basement, new build shortly after final inspection). Leave doors to other rooms slightly open during operation if you want to extend the effect beyond a single room - air naturally mixes throughout a flat.

Comparing operating costs by output class

Since the unit price is only one part of the decision, let's also look at how the purchase investment differs across the presented series - with the same technology (inverter, same brand and series), the price difference is due mainly to the size of the compressor and heat exchangers, i.e. real output, not an unnecessary surcharge for a "higher class".

As you can see, the difference between the 2.5 kW and 3.5 kW variants is relatively small (approx. €34), while the jump to the 5.0 kW variant is more significant - which corresponds to the real jump in output and component size. Practical recommendation: if you're torn between two neighbouring output levels and your room is right at the borderline, it's worth reaching for the more powerful variant - the surcharge is usually smaller than the extra cost and hassle of an undersized unit that can't keep up on the hottest days.

Air conditioning for heating too - does it make sense in Slovakia

Most modern split air conditioners, including the series presented here, also work in air-to-air heat pump mode, meaning they can heat a room as well, not just cool it. For many customers this is a welcome bonus, especially in the transitional seasons (spring, autumn), when it's worth adding a bit of heat without having to start up the whole heating system. However, keep in mind that heating efficiency with an air conditioner drops noticeably at low outdoor temperatures (typically below approximately -5 to -10 °C, depending on the specific model), which is why, in our climate, an air conditioner with a heating function is recommended as a supplementary rather than a primary heat source during the winter months.

The most common myths about air conditioners we encounter

Alongside specific technical questions, customers often repeat claims they've heard from a neighbour, on a discussion forum, or simply remember from the past that are no longer true, or were never entirely accurate. A few of the most widespread ones are worth setting straight.

Myth: Air conditioning causes colds and sore throats

A cold draught aimed directly at the body for a longer time can indeed cause discomfort, especially if the difference between outdoor and indoor temperature is extreme, or if the airflow is directed straight at the neck or back while sitting. The cause, however, is not air conditioning as such, but an incorrectly set louvre direction and too aggressive a target temperature. The recommended difference from the outdoor temperature is approximately 5 °C, and the louvres should be directed diagonally upward or into the room, not directly at the spot where you're sitting or sleeping.

Myth: The more expensive the air conditioner, the automatically better it is

The price within a single series (as we showed in the comparison above) mostly reflects real output - a larger compressor, larger heat exchangers, a more powerful fan. A higher price therefore does not mean a "better" unit in an absolute sense; it means a higher output for a larger space. Buying an oversized unit for a small room doesn't make sense - besides the unnecessarily higher price, it can also cause an unpleasant effect of rapid cooling followed by reheating (so-called cycling), which reduces comfort and shortens the compressor's service life.

Myth: Air conditioning dries the air out so much that it's harmful to health

A slight drop in humidity during cooling does indeed occur (condensation on the evaporator), but in an ordinary living room with a reasonable temperature setting this is usually not pronounced enough to be a health issue. For more sensitive individuals, or with very long operation, the effect can be compensated for with plants in the room, a bowl of water on a radiator outside the cooling season, or, in extreme cases, a humidifier - in practice, though, few people bother, because the real impact tends to be negligible.

Myth: You only need to switch on a dehumidifier once you see condensation on the windows

Condensation on glass is the final stage, by which point air humidity is already significantly elevated. Before that, moisture often accumulates invisibly in poorly ventilated corners, behind wardrobes against the outer wall, or in the attic - that is exactly where mould later appears without you ever noticing a foggy window. Regular measurement with a hygrometer and preventively switching on a dehumidifier before visible symptoms appear is a much more reliable approach than waiting for a misted-up pane.

How to decide if you're still unsure

If, after reading all of the above, you're still not sure, we recommend proceeding in three steps. First, measure the room area precisely and note the orientation of the windows, the size of the glazing, and any heat sources (electronics, kitchen stove) - you will need this data both when choosing the output and when consulting an installation company. Second, decide whether your primary problem is temperature (you need an air conditioner) or humidity (you need a dehumidifier, or possibly both devices independently of each other). Third, if you're torn between two neighbouring output variants, lean towards the more powerful one - the price difference is usually smaller than you'd expect, while an undersized unit will cause you problems throughout the whole season.

For larger or atypical spaces (office open-plan areas, commercial premises, industrial halls) it is always most reliable to have an installation company carry out an on-site inspection - they can also take into account factors that can't be read off a table calculation, such as airflow patterns in the space, the number of people typically present in the room, or the heat losses of the specific building.

Frequently asked questions

Does the air conditioner need to be on all day to work efficiently?

No, quite the opposite. An inverter air conditioner is most economical when it maintains a temperature already reached through gentle output regulation, not when it repeatedly starts up from off to full power. If you're home most of the day, it's worth letting it run continuously at a reasonable temperature (for example 25 °C) instead of switching it on and off.

Can an air conditioner be installed in a rental flat without any work on the façade?

Work on the façade (drilling through the wall for piping, mounting the outdoor unit's bracket) is practically always required with a classic split system, so in a rental relationship the property owner's consent is essential, and possibly also the consent of the owners' association in an apartment building. An alternative without façade work is a portable air conditioner with an exhaust hose through the window, though it has lower efficiency and higher noise compared to a split unit.

How often does the air conditioner filter need to be cleaned?

During the season (June to September under normal use) we recommend visually checking and, if needed, cleaning the filter every 2-4 weeks; with more intensive use or in a dustier environment, even more often. A neglected filter is the most common cause of unnecessarily high consumption and reduced cooling output.

Can I install an air conditioner myself if I have experience with home repairs?

We do not recommend it. Installing a split air conditioner requires working with refrigerant, evacuating the circuit, and professional electrical wiring - besides the safety risk, DIY installation usually also means losing the warranty on the unit. Always leave the installation to a certified installation company.

Is one dehumidifier enough for a whole flat?

It depends on the layout and on where the problem is biggest. In a flat with an open-plan space (kitchen combined with the living room) and doors left slightly open to other rooms, one medium-output dehumidifier may be enough for the whole flat. With several closed rooms that each have their own source of moisture (a bathroom and a laundry room separately), it's more effective to address them separately, or to move the dehumidifier between rooms over time.

Is it worth waiting for an off-season discount, or buying an air conditioner right in summer?

From the point of view of installation company availability, buying outside the main summer season (autumn, winter, early spring) is usually more advantageous - not necessarily in terms of product price, but in terms of the speed and availability of an installation slot - in July and August installation capacity tends to be fully booked and waiting times stretch to weeks.

Do you have a question about this topic?

Can't decide, or dealing with a specific situation in your household? Write to us - we're happy to help.