ᐅ Use an Air Source Heat Pump or Gas and Solar?

Unfortunately, I cannot calculate the heating load because I am missing the necessary data from the architect. We are still at the early stages of planning. So, it is not easy to say based on a single-family house built to KFW 100 standard according to the 2016 Energy Saving Ordinance whether the running costs of a gas boiler are cheaper than those of an air-to-water heat pump, or roughly how high the monthly expenses would be.

Please don’t take the question the wrong way, as I don’t have much knowledge about these topics.

However, since I work in the energy industry, my estimate (based on the current plans and assessments) is that electricity prices will rise in the coming years due to the Renewable Energy Act surcharge and grid fees (power transmission from north to south), while gas prices are expected to remain relatively stable.

My general contractor provided me with a cost-effectiveness analysis for a LWZ 304 from Stiebel Eltron (Stiebel offers a specific tool for commercial customers, tailored to their own products; how objective this really is, you’ll have to judge for yourself; we still plan to have an independent heating load calculation and comparative offers).

KfW55
Heated area 140m² (basement, ground floor, top floor)
Average ceiling height 2.50m (8.2 ft)
4 occupants

Building heating load 3.5 kW
Standard outdoor temperature -14°C (7°F)
Heating limit temperature 10°C (50°F) (is this the balance point?)
Flow temperature 35°C (95°F)
Coverage rate 98%

LWZ304
Monoenergetic
Balance point -5°C (23°F)
Underfloor heating

Domestic hot water normal usage

Cost LWZ including ventilation system without installation: €19,057 (of which €14,500 is for the LWZ unit itself).

The following cost-effectiveness calculation (copied from a table, unformatted):

Consumption-related costs Natural gas Heat pump
Energy price for heat generation [cents/kWh] 7.50 19.00
Energy price for auxiliary power [cents/kWh] 25.00 25.00
Basic annual charge [€] 205.00 67.00
Energy costs of the system [€] 833.00 539.00
Energy costs per heated area [€/m²] 5.95 3.85

Operating costs Natural gas Heat pump
Maintenance and repairs [€/year] 25.00 10.00
Cleaning of exhaust system [€/year] 75.00 0.00
Operating costs of the system [€] 100.00 10.00

Total costs Natural gas Heat pump
Consumption and operating costs [€/year] 933.00 549.00
Investment costs [€] 19,700.00 25,657.00
Capital-related costs [€/year] 1,450.00 1,888.00
Maintenance costs [€/year] 385.00 95.00
Total system costs [€/year] 2,768.00 2,532.00
Total system costs per heated area [€/m²*year] 19.77 18.09

Payback period Your input
Evaluation period [years] 20
Payback period [years] 14

Boundary conditions Your input
Evaluation period 20
Interest rate 4%
Annual price increase natural gas 5%
Annual price increase heat pump electricity 2%

Criticism regarding this:
- I assume installation costs are not included?
- No precise information about the gas system
- Natural gas price increase estimated at 5%, electricity at 2%
- Can the balance point be freely adjusted? Does -5°C (23°F) make sense here, or is that an optimistic assumption?
- What is the lifespan of the equipment? If I have to replace my heating system every 20 years, there isn’t much benefit if break-even is only reached after 15 years.
- Domestic hot water consumption is stated as normal—what does that mean? No baths allowed and only 5 minutes of showering per person?

As mentioned, an independent heating load calculation still needs to be done, and I will get separate quotes from HVAC specialists based on that.

Alright, let him guarantee that then.
He will cover the difference for the first 10 years (of course based on the performance factor of the air-to-water heat pump) –

Questions about the calculation:
Why is the annual basic charge €205 for gas plus €100 for maintenance? Is it really that expensive?
What are the one-time operating costs for the system?
What exactly do maintenance costs include?

He assumes 11.1 MWh and an annual performance factor of 3.9 – not unrealistic at all.

The maintenance cost is €25 for gas, €10 for air-to-water heat pumps, and the chimney sweep fee is €75 for gas and €0 for air-to-water heat pumps.

In total, that amounts to €100 for gas and €10 for air-to-water heat pumps.

I am not sure what is included in the maintenance for gas.

How do you arrive at an annual performance factor of 3.9? The energy per square meter? In that case, for gas it would be over 5, so I think you might be mixing something up. According to Stiebel Eltron, the ventilation unit (LWZ) has an annual performance factor of 3.4 at a standard outside temperature of 2°C (36°F) and a supply temperature of 35°C (95°F).

In our initial meeting, an architect told us that it is still possible to install both solar thermal systems and gas heating, but if you don’t take a KfW loan, no one will check it afterward. Many of his clients continue to just install a gas boiler and forgo anything else. Of course, he is required to inform them about the regulations, but whether the client has solar and a controlled ventilation system installed would no longer be verified.

Is this really credible?

@ Kaspatoo: Thanks for your calculation, very interesting!