Passive house from 2004; cleaning of the ventilation system

Hello everyone,

we are currently considering buying a passive house from 2004. Our biggest question mark is behind the ventilation system installed there and the photovoltaic system.

We had a viewing appointment at the house. Neither the real estate agent nor the owners could provide information about whether the system has been cleaned, whether filters are installed, and whether they have ever been changed, etc. Apparently, the deceased husband of the owner took care of these matters, so no one knows anything about it now. The woman says that the system cannot be cleaned and has no filters. Can that be true? Wouldn't germs inevitably form in such a system?

What also confused us is that the woman has about €300 in electricity costs per month. These are compensated by the photovoltaic system, so there is still a payout from the municipal utilities for 4 more years, but this will then cease, and the €300 would become due. We currently also live in a house with a heat pump and pay significantly less. The other house even has geothermal energy and should therefore be considerably more economical.

Thanks for your help!
Best regards
Tim

Now looking at the system is a matter of 5 minutes. In the rooms, remove the valves and take a look at how it looks. At the installation location of the system, check the filters. The chance that the system has no filters is very low. If the system has valves and pipes (and it does), then these can also be cleaned. Where the electricity costs come from needs to be investigated. Maybe the heat pump is running in emergency mode all the time.

I suspect that it is a pure air-to-air heating system, right? That would explain the high energy costs. Is there perhaps also an electric underfloor heating installed?