ᐅ Which heating system? Air source heat pump or gas?

Hello everyone,

we are planning to build a townhouse with approximately 160m2 (1,722 sq ft) of living space using Poroton T8 blocks with a thickness of 36.5cm (14 inches). The house will also have a fully finished basement that will be heated.

A gas connection is possible in the new development area. I am currently undecided about the heating system, considering either a gas heater or an air-source heat pump. Later on, this system is planned to be combined with a photovoltaic system.

Ground-source or groundwater heat pumps are not an option for me due to the costs involved.

Which type of heating would you choose and for what reasons? I am leaning towards gas heating because I expect it to remain viable for the next 10–15 years. Unfortunately, I find it difficult to make a decision, and a consultation with the consumer advice center didn’t really help.

If you live in a mild climate, choose an air-to-water heat pump. In alpine regions like the Allgäu, it might not be the best option.

Advantages of air-to-water heat pumps:
- Maintenance-free
- No chimney sweep fees
- No chimney required
- No gas connection needed
- No mixing valve / solar thermal system
- No uncertain future costs (such as CO2 taxes)

Common concerns:
- Short lifespan: No one can guarantee this. However, if properly designed and adjusted, without short cycling and with low flow temperatures, there is a good chance for a long service life.

Costs:
In my case, the air-to-water heat pump was cheaper based on total cost of ownership (TCO) calculations. Invest the money saved into better insulation; your heat pump will benefit from it.

We live near Frankfurt am Main. What always makes me skeptical are the numerous articles about inefficient air-source heat pumps and the very low seasonal performance factors. What use is this to me if I end up with excessively high electricity costs?

The inefficiency usually stems from the fact that the entire system design was estimated rather than properly calculated! Room-by-room heating load calculations and low flow temperatures are key to achieving good system efficiency. Unfortunately, many heating installers still rely on outdated practices. Gas and oil systems tend to tolerate some errors in the design.

To put the risk of poor design into perspective:

Assuming an actual heating demand of about 10,000 kWh.

The difference between a seasonal performance factor (SPF) of 3 (poor) and 3.5 (acceptable) results in roughly €10 per month (0.25 €/kWh).

In Frankfurt with a modulating air-to-water heat pump, a seasonal performance factor above 4 should easily be achievable.