ᐅ Possible House Purchase – Air-to-Water Heat Pump Could Become a Money Pit

Hello experts.

A house that was built solidly three years ago (without insulation) is up for sale.
The house is equipped with an air-to-water heat pump as well as a fireplace. There are no solar thermal or photovoltaic systems.
Heating is provided by the air heat pump and the fireplace, and an energy performance certificate is available. The values have varied somewhat over the three years, but well.

The seller gave me the invoice for the heat pump and the underfloor heating yesterday.

How can I tell if this is a "good" energy concept?
Before I buy, I want to make sure I’m not getting into a money pit.

Do I possibly need the exact external wall thickness (which type of masonry), roof insulation, window specifications, etc. for that?

I would appreciate any information. Have a nice evening and best regards, Chris

How high is the electricity bill? How many people live there? Karsten

How can an energy performance certificate fluctuate?

P.S. Electricity consumption does not necessarily provide much information about the heating usage! Especially if the fireplace was in continuous use or if the occupants set the temperature to a maximum of 20°C (68°F).

The house is currently unoccupied. The couple who built the house separated two months ago. Energy consumption for electricity is 24,000 kWh, for wood 15,000 kWh, all given for a period of three years.
Thank you for your feedback.

Let's leave out the wood for now, as I have no idea how much 5000 kWh of wood per year would cost.
Electricity accounts for 8000 kWh annually. Two people, my wife and I, use 2000 kWh per year without the pump for cooking, washing, and similar activities. That amounts to roughly 800 euros. So, heating costs would be 2400 euros per year at our electricity rate, plus the cost of wood. Not exactly cheap. Or am I making an error in my calculations? Karsten

According to the seller, the energy values have fluctuated significantly over the past three years.