What power of a WIFI heater do I need for my room

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What power of a WIFI heater do I need for my room?

This is probably the most important question you need to answer before buying any electric heater – and yet it is a question surprisingly few people ask. Most customers come in saying they "want something to heat the bedroom" or "need a heater for the office", without specifying the exact power. The result? Either the power is insufficient and the room doesn't warm up, or it is unnecessarily oversized and you waste electricity on a device that operates inefficiently.

In this article, we will look at the topic of the power of WIFI heaters systematically – from basic physics through practical calculations to specific recommendations for different types of rooms and buildings. You will also find real-life examples that will help you make the right decision.

Why is the correct power choice crucial?

The power of the heater directly determines how much thermal energy the device can deliver to the room per unit of time. It is given in watts (W) or kilowatts (kW). If the power is too low, the heater will work at 100% continuously, will not reach the desired temperature, and its lifespan will be shortened due to constant load. If the power is too high, the heater will reach the temperature faster, but its control electronics will work in short cycles (on-off), which can lead to uneven heating and unnecessary electricity waste due to incorrect programming.

WIFI heaters have the advantage over traditional electric heaters that they can be programmed and controlled via an app – but even the smartest app cannot compensate for a physical lack of power. Choosing the right model is therefore the foundation on which all intelligent automation is built.

Basic calculation of required power – what physics says

There are several calculation methods, from the simplest estimates to energy audits. For the average customer, the specific power method is sufficient, which takes into account the area of the room and the building's heat loss.

Method 1: Quick estimate (watts per m² rule)

The simplest way: multiply the area of the room (in m²) by a coefficient that depends on the quality of the building's insulation. The result will give you an approximate required thermal power in watts.

Old, uninsulated building (brick without insulation, old windows): 80–120 W/m²
Standard building before 2000 (partially insulated, double-glazed windows): 60–80 W/m²
Insulated building after 2000 (mineral wool, triple-glazed windows): 40–60 W/m²
Low-energy or passive house: 20–40 W/m²

Example: You have a bedroom with an area of 12 m² in an insulated panel apartment from the 90s. You estimate the coefficient at 65 W/m². Calculation: 12 × 65 = 780 W. This means you need a heater with a power of around 750–900 W to cover the heat loss.

Method 2: Calculation according to room volume (more accurate)

Since heat fills the volume, not just the area, a more accurate calculation also takes into account ceiling height. Typically, it is calculated with a value of 30–40 W per m³ of volume in normally insulated buildings.

Example: A living room 5 m × 4 m with a ceiling height of 2.7 m. Volume = 5 × 4 × 2.7 = 54 m³. At a coefficient of 35 W/m³ = 54 × 35 = 1 890 W. This room would require a main heating system with a power of around 2 kW – this is beyond the scope of a standard WIFI heater and rather indicates combined heating or multiple devices.

Factors that affect the required power – not all m² are the same

Calculating based on area is just the beginning. In practice, there are many other factors that can increase or decrease the required power by tens of percent. Over years of sales and project experience, we have identified these key variables:

Room location in the building

A corner room has two external walls instead of one, which means significantly higher heat losses. Similarly, a basement room has the disadvantage of direct contact with the roof and exterior. A ground-floor room above an unheated basement loses heat through the floor as well. On the contrary, a room in the center of an apartment in a panel building, surrounded on all sides by heated neighboring apartments, has minimal heat losses and can be satisfied with a considerably lower output.

Window orientation and glazing

North-facing windows without direct sunlight are always disadvantageous – in winter they lose cold without compensation from solar gains. A south-facing window, on the other hand, can bring passive heat gains on a sunny winter day. The condition of the windows is critical: old single glazing can lose 3–5 times more heat than modern triple glazing with argon. One large old window in a children's room can increase the required heater power by 30–50 %.

Ceiling height

The standard height of 2.4–2.7 m is included in standard calculations. Historic apartments with a height of 3.2–3.5 m or rooms with a gallery have up to 30 % more volume, which accordingly increases the power requirements. Warm air rises, so in rooms with high ceilings, heat accumulates under the ceiling, not where people are.

Purpose of the room and required temperature

Each room has a different recommended minimum temperature:

Living room and dining room: 20–22 °C
Adult bedroom: 17–19 °C
Children's room: 20–22 °C
Bathroom: 22–24 °C
Study and office: 20–21 °C
Corridor and staircase: 15–18 °C
Garage (only as supplementary heating): 5–10 °C

Each additional degree increases heat losses (and thus the required power) by approximately 3–5 %. A bathroom where you require 23 °C instead of 20 °C will need 10–15 % higher power than a room of the same type with a lower required temperature.

Ventilation and air infiltration

Each air exchange in a room means that cold outside air must be heated to room temperature – and that costs energy. Tight plastic windows and doors significantly reduce infiltration (uncontrolled heat loss through gaps), but without mechanical ventilation, problems with humidity and air quality can occur. Rooms with forced ventilation (e.g., a bathroom with a ventilation opening in the façade) lose heat much faster.

Correction factors – how to adjust the basic calculation

After the basic calculation, the result must be adjusted according to real conditions. In practice, we do it as follows:

Corner room (two external walls): + 15 % to the basic calculation
Attic without insulation: + 20–30 %
Old single glazing or window over 20 % of the wall area: + 10–20 %
Room on the north side (permanently without sun): + 10 %
Ceiling height over 3 m: + 10 % for each additional 0.5 m
Room used only occasionally (cottage, garden house): + 15–25 %, because the space needs to be heated after it has cooled down
Room surrounded by heated spaces on all sides: − 10 % (e.g., an internal room in an apartment)

Example calculation: A bedroom of 14 m² in a corner position with a north-facing window, an old two-story apartment block from the 80s (coefficient 75 W/m²). Basic calculation: 14 × 75 = 1 050 W. Corrections: corner position +15 % = +157 W, north-facing window +10 % = +105 W. Total: 1 050 + 157 + 105 = 1 312 W. Reserve 15 %: + 197 W. Result: approx. 1 500 W. In this case, you would choose either the WIFI heater H+h WIFI 1200W as the main heating supplemented by a smaller model, or directly a more powerful device.

Overview of power classes and their typical use

150 W – micro-power for the smallest spaces and supplementary heating

WIFI heater H+h WIFI 150W is intended for spaces where you do not need to significantly change the temperature, but to maintain a pleasant warmth or eliminate cold from a specific cold surface. Typical use: a small bathroom (up to 3–4 m²) in a well-insulated apartment, an entrance hall, a coat closet, a small garden house for pets, or an electric recess under a workbench. This power is not sufficient as the main heating for any living space – it is a supplementary device.

At the same time, it is an excellent device for maintaining temperature (not heating a cold room) in well-insulated small spaces, where other heating (e.g. central heating) maintains the base and the WIFI heater only adjusts the temperature according to current needs.

300 W – small spaces and a supplement to other heating

WIFI heater H+h WIFI 300W covers as main heating spaces up to 5–6 m² in well-insulated buildings (e.g. a bathroom in a new building or a toilet). In older buildings, it is more of a supplementary heating for spaces up to 8 m², where other heating (e.g. district heating) is insufficient for the outer rooms.

Customers most often install it in:

small bathrooms in apartments (3–5 m²)
toilets
closets and entrance halls
small offices or hobby rooms with another heat source

600 W – standard power for smaller living rooms

WIFI heater H+h WIFI 600W is the first power that realistically covers as main heating a small living space – a bedroom or an office in the range of 8–12 m² in a standard insulated house. With good insulation (new building, low-energy building), it also covers spaces up to 14–15 m².

This is the most popular power for bedrooms, children's rooms and home offices in modern buildings. A power of 600 W for one hour of continuous operation creates costs of only around 0.12–0.15 € (at an electricity price of 0.20–0.25 €/kWh), while thanks to the thermostat and WIFI programming, it is not operated continuously, but only when necessary.

900 W – universal power for medium-sized rooms

WIFI heater H+h WIFI 900W is a power that in practice covers most common living rooms in standard buildings. Specification: rooms 12–16 m² in a standard insulated house, or 16–20 m² in a new building or well-reconstructed house. It is also a good choice for larger bedrooms, dining rooms and smaller living rooms.

A big advantage of the 900W model is that it has enough reserve for situations when it is unexpectedly cold outside, when you do not want to ventilate the room especially at night, or when the room has not been heated for a few days (e.g. after a weekend stay outside the house) and it is necessary to heat it up quickly.

1200 W – power for larger spaces and more demanding conditions

WIFI heater H+h WIFI 1200W is the most powerful in the H+h WIFI series and suitable for rooms 16–20 m² in standard buildings or larger spaces in well-insulated buildings. It also covers living rooms, larger offices and offices, where there is a higher rate of heat loss due to a larger number of windows.

Practically speaking: if you have a large living room of 22 m² in a panel apartment in good condition with plastic windows, this power will probably be sufficient. If you have a similarly large living room in an old brick house with old windows and corner exposure, you will need to combine multiple devices or reach for central heating as the primary source.

When to use multiple WIFI heaters instead of one powerful one?

This is a question that customers deal with quite often – they have a larger living room or an open-space office and are wondering whether to buy one powerful heater or two smaller ones. The answer depends on several factors:

Two heaters with lower power placed on different walls of the room ensure a more even distribution of heat than one powerful heater in one corner. This is especially true for long narrow rooms (corridors, long living rooms with a kitchen area) or L-shaped spaces, where one heater cannot reach every corner with heat.

Another advantage of multiple smaller units is backup: if one heater fails or needs service, the other will cover at least the basic heating needs. With a single device in the room, you are completely without heat in the event of a breakdown.

On the other hand, one more powerful heater is cheaper to buy than two devices, has a simpler installation (one power point) and lower programming requirements. For standard-shaped rooms with a central heater location, one device is sufficient.

Practical examples from real customer orders

Example 1: Children's room in a panel apartment

Children's room 11 m², third floor of a panel building from 1978, partially insulated (facade insulation with contact layer was done around 2005), plastic double-glazed windows, the room is internal – adjacent to the hallway and another room. Coefficient: 65 W/m². Basic calculation: 11 × 65 = 715 W. Since the room is not corner and has relatively good neighbors (heated adjacent rooms), we reduce by 10 %: 715 × 0.9 = 643 W. Reserve 15 %: +96 W. Total: approx. 740 W.

Result: WIFI heater H+h WIFI 900W is a logical choice here – it is slightly more powerful than the calculated need (which is intentional, as winter peaks are unpredictable), but it will not be overdimensioned to the point of having problems with the thermostat.

Example 2: Bathroom in an old family house

Bathroom 5.5 m², old family house from 1965, brick walls without contact insulation, old window (one small), desired temperature 23 °C. Coefficient for an old building: 100 W/m². Calculation: 5.5 × 100 = 550 W. Correction for the old window: +15 % = +82 W. Correction for higher desired temperature (23 °C vs. 20 °C): +10 % = +63 W. Total: 695 W. Reserve 20 % (bathroom, where short-term thermal shocks upon entry are common): +139 W. Result: approx. 834 W.

The most suitable model: WIFI heater H+h WIFI 900W – it will quickly heat a small bathroom even in severe winter, but with programming via the app, you can set it so that it does not run at full power continuously.

Example 3: Home office in a new building

Office 16 m² in a new building (construction year 2019, energy certificate A0), triple-glazed windows, southern exposure. Coefficient: 35 W/m². Calculation: 16 × 35 = 560 W. No negative correction factors, southern exposure may even slightly reduce the need, but we keep it as a reserve. Result: approx. 560–600 W.

The ideal model here is WIFI heater H+h WIFI 600W. In a new building with excellent insulation, it is sufficient, and thanks to WIFI programming, you can precisely set it to working hours without unnecessary waste.

WIFI heater as a supplement vs. primary heat source

A very important distinction that customers sometimes overlook: WIFI electric heaters are primarily designed as supplementary or primary heating for individual rooms, not as a heat source for the entire house. If you are considering replacing the entire central heating system with electric heaters, you must be aware that the operating costs of electric heating are significantly higher than those of heat pumps, district or gas heating at today's electricity prices – even with excellent programming and WIFI control.

Where WIFI heaters make economic sense as a primary heat source:

low-energy and passive houses, where heat loss is minimal
occasionally used spaces (cottage, garden house, rented apartment)
rooms where other heating is insufficient or completely absent
spaces where central heating reconstruction is expensive (e.g., installing a radiator in a bathroom is costly)

If you plan to use a WIFI heater as a supplement to existing central heating, the power requirements are lower – the device only "tops up" the temperature beyond what the central heating provides. In such a case, a lower power is sufficient than with full primary use.

Electricity consumption and operating costs

One of the most common customer questions: "How much will it cost me per month?" The answer depends on several variables, but we can provide an approximate calculation.

An electric heater with a thermostat and WIFI programming does not run continuously. A modern electric heater with good regulation runs on average 40–60 % of the time to maintain the set temperature in a well-insulated space (so-called duty cycle). In very well-insulated new buildings, it can be 20–30 % of the time.

Example calculation for a 900W model in a 12 m² bedroom (standard panel, plastic windows):

Power: 900 W = 0.9 kWh per hour at full power
Average duty cycle: 50 %
Effective consumption: 0.9 × 0.5 = 0.45 kWh/h
Operation: heating season approx. 5 months, at night (8 h/day)
Total consumption: 0.45 × 8 × 150 days = 540 kWh per season
Cost at 0.25 €/kWh: approx. 135 € per season for one bedroom

This figure highlights why correct programming via the WIFI app is so important – if you leave the heater on all day when the room is not in use, costs can be two to three times higher. More about programming can be read in the article Programming the timer and heating zones for energy savings in our Knowledge Center.

Most common mistakes when selecting power

Over the years of practice, we have seen these recurring mistakes that customers make when selecting power:

Underestimating heat loss: the customer forgets about old windows, corner location or an uninsulated ceiling and selects a heater with a power lower than needed. Result: the heater runs continuously, the room does not reach the desired temperature, and the customer is dissatisfied.
Measuring area without considering layout: an L-shaped room with an area of 15 m² has completely different requirements than a square 15 m² room, because one heater cannot distribute heat to the distant corners of the L-shape.
Ignoring ceiling height: the customer has a historic apartment with 3.2 m ceilings and calculates the area correctly, but forgets about the extra volume of air that needs to be heated.
Reliance only on the marketing statement "suitable for X m²": this number listed in catalogs is usually an optimistic value for ideal insulation conditions. In real construction, you should expect a lower value.
Not buying a reserve: the customer calculates the exact required power and buys a model that matches the exact calculation result. But the calculation is approximate – winter extremes, changes in weather conditions or deteriorating insulation (e.g., old window seals) can increase the need. Always choose a model that is at least 10–15 % higher than the calculated value.

Tips for efficient heating without unnecessary costs

Selecting the right power is the foundation, but the overall efficiency of the system also depends on how you use it. A few proven tips:

Set a daily temperature curve: at night in the bedroom, 17 °C is sufficient, and before waking up in the morning, let the heater increase to 20 °C. This strategy saves 10–15 % in costs compared to maintaining a higher temperature constantly.
Place the heater correctly: best under a window or on a cold wall – this compensates for cold air flow from the coldest surface and ensures natural circulation of warm air throughout the room. Never place it behind curtains or furniture – the thermostat would register a higher temperature before the whole room is heated.
Use the WIFI functions: remote control via the app allows you to turn on heating just before arriving home without running it all day. For setting up the WIFI connection, read more in the article Setting up the WIFI connection and controlling the heater via the app.
Check window insulation: before installing the heater, it is worth checking the window seals. A faulty seal on an old window can increase heat loss by 20–30 %, which affects not only the power you need but also the operating costs.
Do not ventilate with the heater on: short intensive ventilation (5 minutes with the window fully open) loses less heat than long ventilation by the crack method. Turn off the heater during ventilation and turn it back on after closing the window.

Frequently asked questions (FAQ)

Can I use one 1200W heater for two rooms at the same time?

One heater effectively heats only the space where it is located. Heat transfers partially and unevenly into the adjacent room through open doors – it depends on the size of the opening, layout, and amount of furniture. For real heating of two rooms, it is always better to have a separate device in each. In addition, WIFI heaters have their own thermostat, which regulates the temperature where it is located – not in the adjacent room.

Why does my heater keep running and the room temperature not increase?

This is a classic sign of an undersized unit. The heater runs continuously at 100%, but the heat losses of the room are greater than its heat output. Solution: either replace it with a more powerful model or add a second heater in parallel. The cause may also be old windows, poor sealing, or an un-insulated wall/ceiling, which significantly increase heat losses. Also check the placement – a heater behind curtains or in a cabinet may show a higher temperature at the thermostat, but the room remains cold.

Is a 1200W heater better in a smaller room than a 600W one?

An oversized heater is not necessarily better. The advantage is that it heats the room faster, but then the thermostat turns it off and the temperature drops – short on/off cycles (short duty cycle) may be less comfortable than the smooth operation of a properly sized unit. Moreover, a 1200W heater costs more, even if you buy it for a smaller room. For a small room, a correctly sized power is more efficient and comfortable.

How many m² can a 600W heater cover in an old panel apartment?

In a panel apartment from the 80s that has undergone at least partial insulation (exterior insulation finish system, double-glazed plastic windows), calculate with a coefficient of 65–75 W/m². With 600 W, this gives 8–9 m² as primary heating. For rooms of 10–12 m² in such a building, you should go for a 900W model. If the apartment is not insulated and has old windows, the coefficient is 90–100 W/m² and 600W covers only 6–7 m².

Will WIFI programming affect real electricity consumption?

Yes, and significantly. Customers who actively use WIFI programming with night setback (reducing temperature by 3–5 °C during sleep or absence) report savings of 15–25% compared to constant operation. With a properly set weekly schedule – lower temperature at night, preheating before returning home – operating costs decrease enough to potentially offset the higher purchase price of a WIFI model compared to a simple electric heater without regulation. Read more in the article Programming the timer and heating zones for energy savings.

What to do if you don't know exactly what insulation your house has?

If you don't have access to the project documentation or energy certificate, use a safe method: take the year of construction and basic construction type. Panel building or brick before 1990 with no visible insulation on the façade – calculate with a coefficient of 85–100 W/m². Brick or panel after 1990 or with façade insulation – 65–80 W/m². Solid masonry house with solid slabs and new windows – 50–65 W/m². New construction after 2010 – 35–50 W/m². Always round the result up to the nearest available power.

Conclusion – the right power is an investment in comfort and savings

Selecting the right power for a WIFI heater is not a complicated science, but it does require a bit of attention and basic information about the room and building. An investment in a properly sized unit pays off in the form of better comfort (the room is genuinely heated to the desired temperature), lower operating costs (the heater does not run continuously at full power), and a longer device lifespan (less mechanical stress on the thermostat and heating element).

See an overview of available models in the category WIFI heating devices. For more information on choosing the right model, we recommend the article How to choose a WIFI heater – what to pay attention to before purchase and for proper installation of the selected device, read Installation and mounting of a WIFI heater – step by step.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.