Hello.
Our construction company suggests that we should get a Viessmann Vitodens 200-W gas boiler in the 35 kW (47,000 BTU) version. I am a bit concerned that the gas boiler might be oversized, causing it to operate inefficiently and cycle on and off frequently for short periods. The gas boiler is also available in 13 kW (18,000 BTU), 19 kW (25,800 BTU), and 26 kW (35,300 BTU) versions. According to the manufacturer’s website, the 26 kW (35,300 BTU) or 35 kW (47,000 BTU) models are recommended for single-family homes, while the 13 kW (18,000 BTU) and 19 kW (25,800 BTU) versions are only suggested for apartments.
We will be building a two-story single-family house with approximately 185 m² (2,000 sq ft) and a ventilation system with heat recovery. Two adults and two children want to have showers and keep the house warm. 😉
What do you think about this?
Our construction company suggests that we should get a Viessmann Vitodens 200-W gas boiler in the 35 kW (47,000 BTU) version. I am a bit concerned that the gas boiler might be oversized, causing it to operate inefficiently and cycle on and off frequently for short periods. The gas boiler is also available in 13 kW (18,000 BTU), 19 kW (25,800 BTU), and 26 kW (35,300 BTU) versions. According to the manufacturer’s website, the 26 kW (35,300 BTU) or 35 kW (47,000 BTU) models are recommended for single-family homes, while the 13 kW (18,000 BTU) and 19 kW (25,800 BTU) versions are only suggested for apartments.
We will be building a two-story single-family house with approximately 185 m² (2,000 sq ft) and a ventilation system with heat recovery. Two adults and two children want to have showers and keep the house warm. 😉
What do you think about this?
What does the heating load calculation say, and how is the hot water supply managed?
The heating load at standard outdoor temperature (-10 to -16°C / 14 to 3°F) should not exceed 10 kW in your case! So why install a 35 kW unit? The only exception would be if hot water is supplied using an instantaneous water heater system. But even then, I find 35 kW excessive... The system will short-cycle itself to death.
Please have your heating engineer justify it using the heating load calculation, rather than relying on "we've always done it this way."
The heating load at standard outdoor temperature (-10 to -16°C / 14 to 3°F) should not exceed 10 kW in your case! So why install a 35 kW unit? The only exception would be if hot water is supplied using an instantaneous water heater system. But even then, I find 35 kW excessive... The system will short-cycle itself to death.
Please have your heating engineer justify it using the heating load calculation, rather than relying on "we've always done it this way."
Sorry Nordlys, but in my opinion, this is not the right approach...
A heating load calculation according to DIN EN 12831 should be carried out, based on which the sizing of the boiler is determined as well as the spacing for the underfloor heating or the sizing of the radiators.
A mechanical ventilation system with heat recovery indicates a well-insulated house.
For example, in our case: 160 m² (1722 sq ft), no basement, mechanical ventilation with heat recovery, solar system for domestic hot water, KfW 55 standard => heating load 6.4 kW => 14 kW condensing boiler from Wolf. Our annual consumption is about 850 m³ (30,000 cu ft) of gas.
If the heating system is oversized, this mainly leads to frequent cycling, which in my opinion is not beneficial for its longevity.
Just my two cents... ;-)
EDIT: 2 minutes too late... ;-)
A heating load calculation according to DIN EN 12831 should be carried out, based on which the sizing of the boiler is determined as well as the spacing for the underfloor heating or the sizing of the radiators.
A mechanical ventilation system with heat recovery indicates a well-insulated house.
For example, in our case: 160 m² (1722 sq ft), no basement, mechanical ventilation with heat recovery, solar system for domestic hot water, KfW 55 standard => heating load 6.4 kW => 14 kW condensing boiler from Wolf. Our annual consumption is about 850 m³ (30,000 cu ft) of gas.
If the heating system is oversized, this mainly leads to frequent cycling, which in my opinion is not beneficial for its longevity.
Just my two cents... ;-)
EDIT: 2 minutes too late... ;-)
The heating load for a new build like this is typically around 6-8 kW, especially with controlled ventilation and heat recovery, it tends to be on the lower end.
Anyone who wants to install a 26 kW heat generator for this has definitely chosen the wrong profession. It is simply unfortunate how this industry operates. The system will cycle excessively, which negatively affects the lifespan of the unit. Even with the "smaller" 13 kW option, you end up with hot water similar to that from an instantaneous water heater.
Anyone who wants to install a 26 kW heat generator for this has definitely chosen the wrong profession. It is simply unfortunate how this industry operates. The system will cycle excessively, which negatively affects the lifespan of the unit. Even with the "smaller" 13 kW option, you end up with hot water similar to that from an instantaneous water heater.
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