ᐅ New Heat Pump for an Older Home Without Renovation

Nutshell schrieb:

I have a KFW55 house with solar hot water and gas (8600 kWh gas/year for heating and hot water) and underfloor heating. The new 6.8 kW split air conditioner with 4 indoor units is currently used for heating. Peak load coverage is one issue, but I will also turn off the air conditioner at -10°C (14°F) and rather switch on the gas.

This is optimal: The gas heater then operates nicely in the optimal condensing range. The heat pump of the air conditioner runs efficiently at moderate temperatures. I can calculate when what is worthwhile with the help of my electricity and gas rates.

I just want to point out that your gas heating should always run in the optimal condensing range during heating operation. If not, there would be a significant problem.

Nutshell schrieb:

1. You go with the classic (affordable) developer/general contractor option with gas + solar
-> Affordable? That’s a proper Viessmann system with underfloor heating.

I said "affordable," not bad. Gas has always been cheaper to install than a heat pump.

Nutshell schrieb:

From the start, you should have gone with air conditioning as heating, a heat pump for domestic hot water, or a central on-demand water heater and photovoltaics.
-> I built in 2013. Back then, my gas costs were around €28-40 (about $30-43) per month, so quite manageable. Air-to-air heat pumps weren’t as efficient as they are now.

I know, hindsight is always 20/20, and it’s easy to criticize. However, air conditioning was already efficient and widely installed at that time. Today, such a system could be perfectly integrated into a new build. Indoor units could be installed in walls at suitable locations. You could save on underfloor heating, and so on.

As a consultant, I generally advise against installing new solar thermal systems nowadays. The effort-to-benefit ratio no longer makes economic sense. Existing systems, of course, can remain, as they are better than nothing. For new projects, I clearly recommend (manufacturer-independent) photovoltaic systems combined with heat pumps. In general, these options all share the same common drawback that has been briefly discussed here before: the initial investment is very high. With solar thermal systems, ongoing electricity costs and sometimes significant efficiency losses must not be overlooked. The return on investment (ROI) should be under 10 years for a financially viable solution (excluding environmental motivations and personal interests).

For implementation, the choice of heat pump must be decided on a case-by-case basis, considering whether a hybrid system makes more sense or if a single heat pump alone is sufficient. Heat demand as well as hot water demand are crucial factors.

Overall, I appreciate that these discussions here have already moved in the right direction.

Between air-to-air and air-to-water heat pumps, the comfort factor also needs to be taken into account. For example, warm underfloor heating provides a different kind of warmth compared to warm air blowers. Therefore, there is no one-size-fits-all right or wrong solution.

P.S.: I am advising part-time as a graduate engineer, completely manufacturer-independent, with my focus solely on efficiency and financing. I have no products to sell, as this is a hobby and a service for a good cause.