ᐅ Natural gas consumption with a condensing gas boiler – is it acceptable? Where is the greatest potential for optimization?

Hello everyone,
I would like to get your professional opinion on where there might still be potential to optimize our natural gas consumption. Based on both feel and measured against the calculated energy demand, we seem to be using too much.

Initial situation:

Approximately 185 sqm (2,000 sq ft) of living space
2 full floors, no basement,
Flat roof, 20 cm (8 inches) of insulation between rafters with thermal conductivity 0.035 W/mK plus on average 9 cm (3.5 inches) of insulation above rafters for slope correction
Connected double garage (not heated) and an attached heated technical room within the thermal envelope, no bay windows, projections or similar features
Masonry: 20 cm (8 inches) calcium silicate bricks + 16 cm (6 inches) exterior thermal insulation composite system (ETICS) with thermal conductivity 0.032 W/mK
Gas condensing boiler Brötje WGB Evo 20 G with output range 2.9 - 20.0 kW
Approximately 16 sqm (170 sq ft) of solar thermal panels (in operation since 24.04.19) supporting the heating system
Buffer storage tank with 1,000 liters (265 gallons) volume
Central controlled ventilation system with heat recovery (in operation since 04.10.19, so negligible impact so far)
Preferred room temperature setpoint 25°C (77°F), reduced setpoint 18°C (64°F), heating curve set to 0.64, domestic hot water at 60°C (140°F)
Night setback between 10:00 pm and 5:00 am

Indoor temperatures: 22°C (72°F) living room, 22.5°C (72.5°F) bathroom 1, 21°C (70°F) bathroom 2, hallway 21°C (70°F), bedroom heating basically off, children’s room and office about 20°C (68°F).

2 adults showering daily within normal usage patterns and 1 toddler (3.5 years old), bathing no more than once per week.

Consumption from Nov. 2018 to Nov. 2019 was about 1,250 cubic meters (44,130 cubic feet) of gas, roughly 12,500 kWh. This includes gas used for cooking, which I estimate at no more than 100 cubic meters (3,530 cubic feet). In my opinion, even that is quite high.
Calculated consumption without the controlled ventilation system would be about 10,000 kWh, so actual consumption is approximately 1,500 kWh too high.

Where do you think the greatest potential for optimization lies?
What is your opinion about Brötje boilers?

Good luck
Ippebson

Nowhere, the consumption is fine.

It’s fine. The mechanical ventilation system for indoor air quality was still functional.

Ippebson schrieb:

Where do you think the greatest potential for optimization lies?

Keep the flow temperature as low as possible, see the related thread about the kids’ room. No nighttime setback (which requires a higher flow temperature). The heating system should cycle as little as possible. This way, you improve the efficiency of the condensing effect, and I can also imagine—without knowing the control system behind it—that the solar thermal support becomes more efficient.

However, the overall impact won’t be huge.

First of all, thanks for the feedback!
I’ll note that everything seems fine so far. I would try turning off the night setback.
However, in the related thread (the one about the children’s room), it is mentioned that the heating curve often runs below the one I set, around 0.4 or 0.25.
Is this actually dependent on the type of heating system?

Currently, I have a flow temperature of about 40 degrees Celsius (104°F), assuming this corresponds to the displayed "boiler temperature." It should be like that, right?

Good luck