New construction + exhaust heat pump according to the builder, is a trench collector affordable?

Hello,

I am currently dealing with a new construction project, which, aside from the heating technology, is slowly entering the final phase. Originally, a gas boiler with solar support for domestic hot water was to be used. The house would thus comply with a Kfw70 standard. Bungalow 125sqm living space (4 rooms, kitchen integrated into the living area, bathroom, WC, utility room) Plot 835sqm.

The developer has now introduced an exhaust air heat pump with decentralized ventilation. Additional costs including extra insulation of the floor slab for Kfw55 standard approx. 6-7000 euros. In principle, I think it is good to be independent from fossil fuels, but I have now looked at such a heating system up close and the concept did not fully convince me. Especially the ventilation seemed suspicious to me, as a noticeable cold draft was already perceptible, and overall the rooms felt a bit stuffy.

The developer himself has so far had no experience with the pumps themselves but wants to install some in the future.

In my research on exhaust air pumps, I also came across heat pump technology with trench collectors and find this concept much more interesting.

The fact is, the additional cost compared to the gas boiler of 6-7000 euros represents the upper limit of my budget. So it must not be more expensive.

I am somewhat at a loss as to how to proceed now. How I might possibly determine whether a trench collector is an option and whether it fits within my budget, or whether other pumps with outdoor installation could be considered, or whether my concerns about the exhaust air pump are perhaps unfounded.

Thank you in advance

Trench collector naturally as an alternative to the exhaust air pump. The question is whether this option can be realized without significant additional costs.
Moreover, I am usually only at home in the evening and initially live alone in the house. From that aspect, I do not particularly like the concept of the exhaust air pump, as it practically relies on the energy of the people, used devices, etc.

Trench collector, of course, as an alternative to the exhaust air pump. The question is whether this option can be implemented without significant additional costs.

If you do the trench yourself, usually yes. Gas connection, ST, gas boiler are omitted. Instead, a brine heat pump + material for the collector and if you have a good contractor, you will receive EUR 4,000 from BAFA as a subsidy for the brine heat pump as innovation funding for new buildings.

But you have to engage intensively with this and have the right partner, i.e., general contractor/general planner/architect or similar as well as a contractor. With a property developer, I would definitely not consider this!!!

Since my developer has not installed such heating systems before, it is naturally difficult. Therefore, I am now trying to gather some information myself. Besides gas, only a heat pump with outdoor installation or possibly a trench collector is an option. Everything else does not fit the budget.

A developer sells finished houses along with the land, it is rather unusual that you are allowed to intervene so deeply in their planning and probably not advisable either.

Are you sure you are talking to a developer?

Oops, I seem to have made a mistake. It will of course be an individual new build on a separately purchased plot of land. So through a construction company.