What gas boiler for a 150m² house? We explain the required boiler power in kW.

✅ What Gas Boiler for a 150m² House and What to Consider?

Condensing gas boilers provide an excellent heating system, especially for new, relatively energy-efficient buildings. If you're wondering what gas boiler to choose for a 150m² house, it's likely new construction based on the typical size of today's homes. However, a condensing boiler can also serve older, less energy-efficient buildings.

Our article will guide you on what to pay attention to—not just the kW power required for a 150m² house.

Read to the end, especially if you plan to install a gas boiler in an older building—we address this aspect in detail. We will start with new construction.

Factors Influencing the Choice of a Gas Boiler for a House

While gas or other fuel boilers are mainly selected based on floor area, whether the house is old or new construction also significantly impacts the choice. Older buildings typically have heat losses up to 80% higher than newer ones. Consider the year of construction, the condition of windows, roof, floor insulation, and whether the building is insulated.

Radiators vs. Underfloor Heating - Difference from the Gas Boiler's Perspective

Another critical factor is whether the house uses radiators (older or newer types) or underfloor heating. Underfloor heating is more advantageous since gas boilers (like heat pumps) perform better and are more energy-efficient in low-temperature installations, which is essential for condensing. Condensation is a more energy-efficient heat production process achievable only at relatively low temperatures, excluding traditional radiators.

• We have already written in detail about condensation and the operation of a gas boiler on our blog. Check it out. ☑️

What Type of Gas Boiler for a 150m² House in New Construction?

✅ What type of gas boiler for a 150m² house? Single-function or dual-function?

For relatively new homes with modern heating systems, a dual-function gas boiler is generally recommended. These boilers are compact, do not require a large boiler room, and have an aesthetically pleasing design, suitable for installation in places like bathrooms. Usually, these gas boilers are wall-mounted. Single-function boilers are more suitable for larger buildings with higher water usage due to more occupants and bathrooms.

Required Boiler Power for a 150m² House

For heating a new house, approximately 6 kW is needed per 100m², sometimes also represented as 0.6 kW per 10m², which means the same. However, additional power is necessary to provide domestic hot water for the residents.

✅ According to our recommendations, a gas boiler with a power of min. 12-15 kW should be chosen for a 150m² house, depending on the level of insulation.

This is, of course, the minimum because you might not find a gas boiler with this exact power in the nearest stores. Therefore, the boiler should be slightly oversized—so 12-15 kW is treated as a minimum. Very often, the installation team will recommend a popular size, such as 24 kW, which is a classic solution. Gas boilers have the ability to modulate, i.e., to adjust their operation to real needs. Oversizing the boiler will not mean an exorbitantly higher price.

Will a Larger Gas Boiler Consume More Gas?

No. There is no need to fear oversizing a gas boiler; it will not consume more gas. This is very easy to explain—today's gas boilers are very modern devices, equipped with temperature sensors that will turn off automatically once the desired temperature is reached. The gas flow and its consumption will then be cut off immediately, and you won't pay more for your bills. Boilers have the ability to modulate—i.e., adjust their power to the building's needs, ensuring that gas consumption remains at an appropriate level.

✅ To ensure that all this automation works efficiently even after many years and to guarantee low gas consumption over many seasons, regular inspections of the gas boiler should be performed (most manufacturers recommend once a year).

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NT Ba-16-40

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Specific Models of Gas Boilers for a 150m² House

First and foremost, we want to highlight that our suggestions are completely independent; we do not sell gas boilers, which makes us credible in this matter. This is not a sponsored article, and our recommendations are, of course, subjective. Below are examples of boilers with good reviews and with which we have had positive experiences—these are suitable for a 150m² house.

• Viessmann Vitodens 050-W B0KA 24 kW - dual-function condensing boiler
• Vaillant 1-f VC 20CS/1-5 (H-PL) ecoTEC PLUS - single-function condensing gas boiler
• Termet Gold Plus 25 kW - single-function condensing gas boiler
• Ariston 2-f Alteas One Net 24 kW - dual-function condensing gas boiler
• Ariston 1-f GENUS ONE SYSTEM 24 kW - single-function gas boiler
• De Dietrich 2-f Inidens 20/24 MI - condensing gas boiler
• Saunier Duval Immergas 2-f VICTRIX TERA 28 1 - dual-function gas boiler

These manufacturers are also relatively low-maintenance. These are products from well-known brands, and finding a service technician for them should not be difficult.

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What Gas Boiler for an Old 150m² House with an Old Heating System?

The heat demand in an old house is significantly higher than in a new one, which is obvious. For such a building, you would select about 10-12 kW per 100m², though 12 kW would only be necessary for houses with extreme heat losses. This raises the question of whether gas should be installed in such a house, and surely those installing gas in an old house have encountered this issue.

Gas is suitable for an old house, but you must ensure thermal modernization. Radical thermal modernization is often very financially demanding, so if the situation requires it, the work should be spread over several seasons. Initially, focus on windows and radiators. If replacing the entire installation is not feasible, start with radiators and replace them with newer types that contain three times less water. Subsequently, insulate the building. In this situation, for a 150m² old house, you would typically select 50-60% more kW for the gas boiler than for a new house.

✅ In summary, for an old 150m² house, a gas boiler with a power of around 20-24 kW should be chosen, depending on the building's insulation.

How to Connect a Gas Boiler in an Old Building? How to Protect the Boiler from the Impact of the Old Installation?

✅ House with an old and dirty open system installation. How to connect a gas boiler to this?

A modern gas boiler cannot operate in an open system, which is typical for old installations. An open system means the circulating water has constant access to air in an open overflow tank. Air access causes water evaporation, necessitating its replenishment. The influx of new water, containing minerals, continuously renews its potential for scale and lime deposits, especially if you have hard water, which is a common issue. Therefore, manufacturers of modern heating sources—gas boilers or heat pumps—do not allow these devices to be used in an open system, risking the loss of warranty.

Moreover, the old installation contains a lot of accumulated deposits and dust over the years, which can damage the gas boiler's automation.

Dividing the System into Open and Closed Circuits and Installing the Gas Boiler in the Closed Part

When installing a gas boiler in an old building with an unmodernized installation, divide the heating system into two parts: one being a short circuit closed system where the boiler will be located. The rest of the system remains in the old open circuit. The connection between the two systems will be through a plate heat exchanger for the gas boiler. The heat exchanger, if properly selected, will transfer heat from the closed system to the open system, i.e., to the radiators. This is essential to remember, although ideally, the entire system should be converted to a closed system, but this essentially means creating a new heating system in the old building.

If full modernization of the installation is not possible, at least reduce the destructive impact of hard water in the open system on radiators, etc., by installing water softeners. Maintenance-free galvanic softeners, such as IPSE, are the best for scale prevention.

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