Is a brine-water heat pump still worthwhile with KfW 40+?

The most important argument for a ground-source heat pump is actually that you simply can't find a suitable location for an air-to-water heat pump. ;-)

If necessary, indoor installation. Essentially with supply and exhaust air like with controlled residential ventilation. There will (almost) never be a shortage of locations for an air-to-water heat pump.

My personal opinion: Ground source heat pumps are no longer worth it from KfW40 onwards. Because the additional cost will never be recovered through lower heating costs. Example: 150 sqm house: heating costs with air-to-water heat pump €600, with ground source heat pump 20% better = €480. Additional cost from air-to-water heat pump to ground source heat pump €6,000 (?), thus payback period of 50 years. Everything can be roughly and easily calculated.

For rentals, definitely air-to-water heat pumps, see post from

However, the calculation is very simplified. You assume that electricity costs remain constant. How likely is that? The higher the electricity costs, the greater the savings...

If necessary, indoor installation. Basically with supply and exhaust air like in controlled residential ventilation. At the location, there will (almost) never be a shortage of air for an air-to-water heat pump.

There may be solutions, but indoors would not have been an option for us.
Luckily, we found a place outside.
If there had been the terrace or the entrance there, I would have preferred to invest in a ground-source heat pump.

But the calculation is very simplified. You assume that electricity costs remain constant. How likely is that? The higher the electricity costs, the greater the savings...

No one has a crystal ball, but then you would of course also have to consider the interest on the drilling costs.
There are many variants here again: simple loan, stocks, real estate, ...
Which then initially makes ground-source heat pumps financially even less attractive.

But there are few reasons why electricity should become significantly more expensive.
Electricity from wind or solar currently costs just 3-8 cents/kWh to produce.

But there are few reasons why electricity should become significantly more expensive. Electricity from wind or sun currently costs just 3-8 cents/kWh to produce.

Tell that to those who sell it. :D

No one has crystal balls, but then of course you would have to take into account the interest on the drilling costs as well. There are again many different variants: simple loans, stocks, real estate, ... Which initially makes the brine-water heat pump financially even less attractive.

But there are few reasons why electricity should become significantly more expensive. Electricity from wind or solar currently costs just 3-8 cents/kWh in production.

Why is the expensive option of deep drilling always being talked about? Surface collectors did not have any additional cost compared to an air-water heat pump here. I think they usually don’t even cost half as much as deep drilling. But you do need a larger plot of land for that...

Why is it always the expensive version of the deep drilling being talked about? But for that, you need a larger property...

That gives you an immediate answer. ;-) But there are other reasons. For example, my impression is that ground collectors are only offered by a few companies. Doing it yourself is also not an option for everyone. Basically, however, it is a good option that should be considered more often.

Ground collectors did not cost more than an air-water heat pump for us. I think they normally cost not even half as much as deep drilling.

How now, no extra cost or half the extra cost? How was the collector installed at your place?