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What is the yearly gas consumption for heating a 100 m2 appartment in Slovenia with a ceiling height of 290 cm? The appartment is 200 years old, but has been renovated in 2023. It used floor heating, the windows are new and the walls (15 cm styrofoam) and the ceiling have been insulated.

Gas is also used for heating the sanitary water for 2 people.

Thanks for the detailed info — it really helps to give a more accurate estimate! Let’s break it down.

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### 🔢 **Assumptions and Inputs:**

- **Location:** Slovenia (moderate continental climate — heating season is roughly Oct–Apr)
- **Apartment size:** 100 m²
- **Ceiling height:** 2.9 m → total volume = 290 m³
- **Building type:** 200 years old, but fully renovated in 2023:
  - New windows (likely double or triple glazed)
  - 15 cm wall insulation (styrofoam)
  - Ceiling insulation
  - Floor heating (efficient at lower temps)
- **Occupants:** 2 people
- **Gas usage:** space heating + domestic hot water (DHW)

---

### 🔥 **Heating Energy Estimate:**

Given your renovation, the apartment likely falls into the **B or C energy class**, depending on renovation quality and tightness. Based on this and average consumption data:

| Energy Class | kWh/m²/year |
|--------------|-------------|
| A+           | <10         |
| A            | 10–25       |
| B            | 25–45       |
| C            | 45–60       |
| D (old)      | 60–100+     |

Since your apartment is well-insulated with modern systems, a **realistic range would be 35–50 kWh/m²/year** for heating.

- **Space Heating Energy Need:**
  - Lower estimate: 35 kWh/m² → 3,500 kWh/year
  - Upper estimate: 50 kWh/m² → 5,000 kWh/year

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### 🚿 **Sanitary Water Heating:**

- Average use: ~800–1,200 kWh/year for 2 people
- Let’s assume **1,000 kWh/year** for both.

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### 🔧 **Total Annual Gas Consumption (in kWh):**

| Purpose            | Lower Estimate | Upper Estimate |
|--------------------|----------------|----------------|
| Space heating      | 3,500 kWh      | 5,000 kWh      |
| Sanitary hot water | 1,000 kWh      | 1,200 kWh      |
| **Total**          | **4,500 kWh**  | **6,200 kWh**  |

---

### 🔄 **Convert to Cubic Meters of Gas:**

Natural gas has an energy content of approx **10.5 kWh/m³**.

| Estimate Type | kWh/year | m³/year (approx) |
|---------------|----------|------------------|
| Low           | 4,500    | ~430 m³          |
| High          | 6,200    | ~590 m³          |

---

### ✅ **Final Estimate:**

👉 **Yearly gas consumption: ~430–590 m³**  
(depending on insulation quality, usage habits, and actual heating needs)

Let me know if you want a breakdown in EUR too, based on current gas prices in Slovenia.

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What if the wall insulation is actually 5 cm?

Great follow-up — 5 cm of wall insulation makes a noticeable difference. Let’s adjust the estimate accordingly.

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### 🧱 Updated Insulation Details:

- **Walls:** Only **5 cm of Styrofoam** — which is on the **thin side** by modern standards (typically 10–15 cm is recommended).
- **Ceiling + Windows:** Still well insulated
- **Floor heating:** Efficient system remains unchanged

This change will likely bump your heating demand up one category. Your apartment now likely falls between **energy class C and D**, instead of B–C.

---

### 🔥 **Adjusted Heating Energy Need:**

Let’s update the **space heating estimate** accordingly:

| Category     | kWh/m²/year |
|--------------|-------------|
| Moderate insulation | 50–70 kWh/m²/year |

- Lower estimate: 50 kWh/m² → 5,000 kWh/year
- Upper estimate: 70 kWh/m² → 7,000 kWh/year

Sanitary hot water remains unchanged at **~1,000–1,200 kWh/year**.

---

### 🔧 **New Total Annual Gas Consumption (in kWh):**

| Purpose            | Lower Estimate | Upper Estimate |
|--------------------|----------------|----------------|
| Space heating      | 5,000 kWh      | 7,000 kWh      |
| Sanitary hot water | 1,000 kWh      | 1,200 kWh      |
| **Total**          | **6,000 kWh**  | **8,200 kWh**  |

---

### 🔄 **Converted to Cubic Meters (m³) of Gas:**

Using 1 m³ of gas ≈ 10.5 kWh:

| Estimate Type | kWh/year | m³/year (approx) |
|---------------|----------|------------------|
| Low           | 6,000    | ~570 m³          |
| High          | 8,200    | ~780 m³          |

---

### ✅ **Revised Final Estimate:**

👉 **Yearly gas consumption: ~570–780 m³**

So with only 5 cm of insulation on the walls, your gas usage could increase by roughly **140–190 m³ per year**, compared to better-insulated walls (15 cm). Let me know if you'd like cost estimates or tips on improving efficiency further.

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Same question for the low-enery pre-fab 150 m2 house in Slovenia, built in 2009. The ceiling height is 250 cm. It uses floor heating. Gas is NOT used for heating the sanitary water.

Nice — a 2009 low-energy prefabricated house is a very different scenario. Let's run the numbers!

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### 🏠 **Home Details:**

- **Type:** Low-energy prefabricated house (built in 2009)
- **Size:** 150 m²
- **Ceiling height:** 2.5 m → Volume = 375 m³
- **Heating:** Floor heating
- **Insulation:** Likely good — prefab houses from that era often exceed minimum standards
- **Windows:** Likely double-glazed, airtight
- **Sanitary hot water:** **NOT using gas**
- **Occupants:** Not specified, but doesn't impact much since DHW is excluded

---

### 🌡️ **Heating Energy Estimate:**

2009 low-energy homes in Slovenia usually fall into **energy class B or even A**, especially prefabs. 

| Energy Class | kWh/m²/year |
|--------------|-------------|
| A            | 10–25       |
| B            | 25–45       |

Let’s assume a realistic range of **20–35 kWh/m²/year** for **space heating**.

- Lower estimate: 20 × 150 = **3,000 kWh/year**
- Upper estimate: 35 × 150 = **5,250 kWh/year**

---

### 🔄 **Convert to Cubic Meters of Gas:**

Using **1 m³ of gas ≈ 10.5 kWh**:

| Estimate Type | kWh/year | m³/year (approx) |
|---------------|----------|------------------|
| Low           | 3,000    | ~285 m³          |
| High          | 5,250    | ~500 m³          |

---

### ✅ **Final Estimate (Space Heating Only):**

👉 **Yearly gas consumption: ~285–500 m³**  
(Depending on insulation, thermostat settings, and occupancy habits)

Let me know if you want to compare this with electric heat pumps or pellet systems in terms of cost or efficiency!