The wrong BTU is the number one cause of an overworked air conditioner, a high electricity bill and constant discomfort. Whether you are cooling a 15 m² bedroom, a 40 m² living room or an office, this article gives you the exact formula, a ready-made table and specific models from our catalogso you choose right the first time.
👉 Short answer: For a standard room with a ceiling height of up to 2,7 m, allow about 350–450 BTU per square meter. Rough guide: 15 m² → 7 000 BTU, 25 m² → 9 000 BTU, 35 m² → 12 000 BTU, 50 m² → 18 000 BTU. Add +10–15% for top-floor rooms, south-facing rooms or rooms with large windows.
What is BTU and why does it matter?
BTU (British Thermal Unit) is a unit of thermal energy. For air conditioners, it shows how much heat the unit can remove from (or add to) a room in 1 hour. The higher the BTU, the more powerful the air conditioner.
In Europe and Bulgaria, manufacturers increasingly also state capacity in kW (kilowatts). The conversion is simple: 1 kW = 3 412 BTU/h. Popular residential air conditioners come in a range of 7 000 – 36 000 BTU, which corresponds to roughly 2,0 – 10,5 kW.
💡 Why does BTU matter so much?
- ❄️ Too few BTU — the air conditioner runs nonstop, doesn’t cool enough, uses more electricity and wears out quickly.
- 🔥 Too many BTU — the unit switches on and off too often (so-called “short cycling”), doesn’t remove humidity and creates cold spots.
- ✅ The right BTU — even cooling/heating, lower power consumption and a long service life.
How do you calculate the BTU you need?
The basic formula used by HVAC professionals is:
BTU = Area (m²) × 100 W/m² × 3.412
Or more simply: Area (m²) × 350 BTU/m²
This formula gives a starting point under standard conditions (2,7 m ceiling height, normal insulation, moderate sun).
Example calculation
For a room of 25 m²: 25 × 350 = 8 750 BTU → you choose a 9 000 BTU model (the nearest standard size up).
Standard capacities on the market are: 7 000 / 9 000 / 12 000 / 18 000 / 24 000 / 36 000 BTU. Always round up to the next standard size.
BTU → room area table
The table below is based on standard residential conditions in Bulgaria: 2,6–2,8 m ceilings, good insulation, moderate sun exposure. For specific conditions, see the adjustment factors below.
| Room area | Required BTU | Capacity (kW) | Best for | Price from (€) |
|---|---|---|---|---|
| up to 15 m² | 7 000 BTU | 2,0 kW | Small bedroom, kids’ room, study | from 270 € |
| 15 – 25 m² | 9 000 BTU | 2,5 kW | Bedroom, small living/dining room | from 320 € |
| 25 – 35 m² | 12 000 BTU | 3,5 kW | Living room, large bedroom, office for up to 4 people | from 430 € |
| 35 – 50 m² | 18 000 BTU | 5,0 kW | Large living room, open space with up to 6 workstations | from 590 € |
| 50 – 70 m² | 24 000 BTU | 7,0 kW | Large living area, small retail premises | from 780 € |
| 70 – 100 m² | 36 000 BTU | 10,0 kW | Large halls, restaurants, showrooms | from 1 200 € |
* Prices are approximate, excluding installation. See current offers in our online shop.
Quick BTU guide
up to 15 m²
15–25 m²
25–35 m²
35–50 m²
50–70 m²
70–100 m²
Factors That Affect Your BTU Choice
Floor area is just a starting point. In practice, professionals take into account a number of additional parameters that can increase the BTU you need by up to 30–50%.
Sun exposure
A room with south- or west-facing windows gets significantly more heat. Add +10–15% BTU to the base calculation.
Insulation and construction
Old panel blocks without retrofit insulation lose a lot of energy. For uninsulated buildings, add +15–20% to the calculated BTU.
Ceiling height
The formula assumes a 2,7 m ceiling. At 3,0 m or more, multiply the BTU by a factor of 1,10–1,15.
Number of people
Each person gives off about 100 W of heat. For an office with 6+ employees, add at least 2 000 BTU extra.
Equipment and appliances
Computers, servers, ovens, refrigerators — they all generate extra heat. In offices with a lot of equipment, add +10%.
Climate zone
Varna and the Black Sea coast have hotter, more humid summers than Veliko Tarnovo or Smolyan. For coastal properties, add +5–10%.
Free consultation: If you are not sure which model you need, our specialists will calculate the exact BTU for your room. Contact us or see the Frequently asked questions.
BTU for different types of rooms
Different rooms have different requirements even with the same floor area. Here is a practical guide:
| Room type | Typical area | Recommended BTU | Comment |
|---|---|---|---|
| Kids’ room / Study | 10–18 m² | 7 000 – 9 000 | Pay attention to the noise level — choose ≤22 dB |
| Bedroom | 14–22 m² | 9 000 – 12 000 | Quiet models with a night mode; Daikin Perfera is a top choice |
| Living room | 25–45 m² | 12 000 – 18 000 | With an open-plan kitchen, increase by 10–15% |
| Office (up to 6 employees) | 20–35 m² | 12 000 – 18 000 | Add 400 BTU per employee and per computer |
| Restaurant / Café | 40–80 m² | 24 000 – 36 000 | Consider a cassette or ducted air conditioner |
| Shop / Showroom | 50–100 m² | 24 000 – 48 000 | With south-facing shop windows, add +20%; VRF systems for > 100 m² |
Which Air Conditioners Match Which BTU?
At Svit Komfortu we offer a full range of inverter air conditioners from leading global brands. Here are our top picks by BTU:
9 000 BTU — Bedrooms and small rooms (up to 25 m²)
2,5 kW cooling / 3,2 kW heating
The ideal choice for a bedroom or kids’ room. Look for models with a night mode and a noise level below 22 dB. Daikin Sensira 9 000 BTU is as quiet as a library — just 19 dB in night mode.
⚡ A++
🔇 19–22 dB
💶 from 320 €
✅ Ideal for: Bedroom, kids’ room, study, small office
12 000 BTU — Living rooms and medium rooms (25–35 m²)
3,5 kW cooling / 4,0 kW heating
The most versatile size — it covers 80% of typical living rooms in Bulgaria. Gree Amber 12 000 BTU offers class A+++ and operation at -25°C, which matters for winter heating.
⚡ A+++
🌡️ down to -25°C
💶 from 430 €
✅ Ideal for: Living room, dining room, large bedroom, office for 4–5 people
18 000 BTU — Large living room or open space (35–50 m²)
5,0 kW cooling / 5,5 kW heating
For spacious living rooms, open-plan kitchen-dining areas or offices with 5–7 workstations. AUX Freedom 18 000 BTU is an excellent choice with good value for money at this capacity.
⚡ A++
📶 WiFi
💶 from 590 €
✅ Ideal for: Open space, large living area, small retail premises
🛒 Browse the full catalog
Over 600 models from AUX, Daikin, Gree, LG, Mitsubishi and more. Filter by BTU, area and budget — open the shop →
5 Steps to Choosing the Right BTU
Measure the exact area
Measure the length × width of the room in meters. For L-shaped or irregular rooms, split them into sections and add them up. Don’t forget: if the air conditioner will also serve a hallway or kitchen, add their area too.
Determine the adjustment factors
Answer these questions: Are the windows south-facing? (+10%) Is the building insulated? (no adjustment) Ceiling above 2,8 m? (+10%) More than 4 people/devices? (+5–10%). Add up the percentage adjustments and apply them to the base BTU.
Choose the energy class
In Bulgaria, with an air conditioner rated A+++ you save up to 40% on electricity compared to class A. If you use the air conditioner for heating and cooling 8+ months a year, the more expensive A+++ model pays for itself in 2–3 seasons. See all inverter air conditioners with A++ and A+++ energy class.
Consider the extra features
For a bedroom, be sure to check: night mode (noise level ≤22 dB) and the “Good Sleep” function (gradual temperature change). For an office — Wi-Fi control and a timer. For allergy sufferers — a HEPA or ionizing filter.
Book professional installation
Even the perfect air conditioner will perform poorly if installed incorrectly. The positioning of the indoor unit, the length of the copper pipes and the correct refrigerant charge are key. Our certified installers in Varna work 7 days a week.
Installation and Warranty — What the Service Includes
Buying the right air conditioner is only half the job. Quality installation is a requirement for the warranty and for efficient operation of the unit. At Svit Komfortu we offer a complete package:
1. Consultation
Free, online or in person. We calculate the BTU for your property.
2. Order
Online or at our showroom. Delivery within 1–3 business days.
3. Installation
Certified technician, full set of materials, site cleanup.
4. Warranty
2-year official warranty + 1-year installation warranty.
- ✅
Installation includes: indoor and outdoor unit, copper pipes up to 3 m, electrical cable, outdoor unit bracket and R32 refrigerant charge. - ✅
We work in Varna and the region — see installation prices for Varna. For properties outside Varna, contact us for a quote. - ✅
All installers are certified under the F-Gas Regulation and work with original materials and tools. - ✅
Installation within 48 hours of order confirmation (subject to availability).
Frequently Asked Questions About BTU and Air Conditioners
How many BTU do I need for a 20 m² room?
For a 20 m² room under standard conditions (2,7 m ceiling, normal insulation, moderate sun), you need about 7 000 BTU. If the room has south- or west-facing windows, choose 9 000 BTU. See our 9 000 BTU inverter air conditioners.
How many BTU do I need for a 30 m² room?
For 30 m², the basic calculation gives about 10 500 BTU. Round up to the standard size — 12 000 BTU. We recommend Daikin Sensira 12 000 BTU or Gree Amber 12 000 BTU — both models are A+++ rated and work at -20°C.
Is it better to get a more powerful air conditioner “just in case”?
No — an oversized air conditioner is almost as bad as an undersized one. A unit with too many BTU reaches the set temperature very quickly but fails to dry the air enough — the result is unpleasant humidity even at a cool temperature. Round up only one size, no more.
What is the difference between BTU and kW?
BTU/h and kW measure the same thing — thermal capacity. The conversion is simple: 1 kW = 3 412 BTU/h. A 12 000 BTU air conditioner = 3,5 kW. On the European market, manufacturers increasingly state capacity in kW, but BTU remains the standard in specifications.
Can one air conditioner heat the whole home?
A single wall-mounted air conditioner effectively serves only the room it is installed in. For heating a whole apartment, consider a multi-split system (1 outdoor unit + 2–4 indoor units) or an air-to-water heat pump with underfloor heating. Contact us for a free design.
Does a higher-BTU air conditioner use more electricity?
With an inverter air conditioner — not necessarily. The inverter compressor adjusts its output to demand. An 18 000 BTU air conditioner at half load (for a room that needs only 9 000 BTU) will run at about 50% capacity and use proportionally less electricity — but its efficiency will be lower than optimal. That is why the right size is actually the most economical one.
How much does air conditioner installation cost?
Standard installation of a wall-mounted air conditioner (copper pipes up to 3 m, electrical cable, bracket) in Varna starts from 120 €. With longer pipes or specific conditions (terrace, brick wall, higher floor), the price may be higher. See detailed prices and terms on the page Air conditioner installation in Varna.
What our customers say
★★★★★
“I used the table from this article and got a 12 000 BTU unit for our 28 m² living room. Perfect cooling, it has never overheated once. Installation took half a day, and the guys were very neat.”
★★★★★
“I consulted the team before buying — they explained in detail why our office needed 18 000 BTU rather than 12 000 because of the sunny side. The air conditioner works great even at 40°C outside.”
★★★★★
“I finally understand what BTU means! The article is clearly written, without unnecessary complexity. I got a Daikin 9 000 BTU for the bedroom and it runs silently — I don’t notice it at night.”
Find the Right Air Conditioner for Your Home
Over 600 models with filters by BTU, area and budget. Free delivery + certified installation in Varna and the region. Browse our air conditioners in Varna with delivery and installation. Need service? See air conditioner repair in Varna.
