ᐅ Heating System Upgrade for Existing Buildings – Condensing Boiler / Air-to-Water Heat Pump / Air Source Heat Pump

Hello dear forum,

I am new here and this is my first post. I would be very grateful if anyone could help me with my question/problem.

Starting point:
We are about to buy a single-family house (built in 1959/60; living area approx. 170sqm (1830 sq ft) – 65sqm (700 sq ft) first floor, 65sqm (700 sq ft) second floor, 40sqm (430 sq ft) attic). The windows were replaced in 2005 (Uw-value 1.2), we will reroof and insulate the roof (U-value 0.14), possibly also insulate the basement ceiling – everything else is still in the “original condition.” Four of us will live in the house (2 adults + 2 children). The attic will be converted into living space. There is an old gas boiler (not condensing) in the basement and old cast iron radiators throughout the house. Additionally, we will renew the electrical system and renovate all the floors.

The key question now is: What heating system should we choose?
Since the house was previously occupied only by an elderly lady, there is no reliable data to estimate our future heating demand. Naturally, we would prefer to move away from fossil fuels and install an air-to-water heat pump combined with underfloor heating and photovoltaic panels (without subsidies, this would definitely cost about 65K) – however, this would exceed our budget. Without photovoltaic, I am also quite worried that the electricity costs could skyrocket. As a compromise, we have now focused on the following option: installation of a gas condensing boiler for heating and a domestic hot water heat pump (DHW HP) for hot water production – the ability to reduce the condensing boiler’s use during warmer months seems very attractive. Besides the cost aspect (which is completely acceptable to us, both initially and ongoing), the sustainability aspect also plays a role here (of course, a DHW HP alone is not a huge lever). At the same time, we are thinking about switching to underfloor heating on the ground floor and low-temperature radiators on the first and second floors. The idea behind this is to create an infrastructure that would allow us to switch to a heat pump fairly easily in the future. We would also gain reliable data regarding heat and heating demand. We wouldn’t have to install photovoltaic on the roof immediately but could add it later, either gradually or all at once.

How do you assess my approach? Does it sound realistic and reasonable to you, especially considering the current context (war, energy transition/costs, etc.)? I understand there is no perfect solution, but I would like to make a well-informed decision that makes economic and ecological sense in the short and long term. Maybe there are alternatives I haven’t considered yet.

A little about me: I am unfortunately not very skilled technically and have very little experience. However, I have noticed that I can quite quickly get to grips with unfamiliar topics and have a steeper learning curve than expected 🙂

I look forward to your feedback.

Best regards,
Christian

In my opinion, the most important thing is to install the underfloor heating BEFORE moving in. Since subsidies are only available if you install a heat pump at the same time, this is probably the "bitter pill" to swallow. But if you don’t do it now, the opportunity is gone and you’ll regret it for the next 40 years. In every second heat pump thread here, you can read the phrase "Unfortunately not possible, we are already living in the house..."

Chrizz72 schrieb:

Of course, we would like to move away from fossil fuels and install an air-to-water heat pump combined with underfloor heating and photovoltaic panels (without deducting subsidies, this would probably cost us around 65,000€) – but this plan would exceed our budget. If we forgo the photovoltaic system, I am also quite worried that our electricity costs will skyrocket.

An air-to-water heat pump with underfloor heating is a good idea. However, the windows are not ideal. If the insulation on the upper and lower floors is done properly and thoroughly, you can achieve a reasonable electricity consumption (based on my own experience last year, since my house will receive external thermal insulation this year).
After that, have an engineering office perform all calculations. For underfloor heating, pipe spacing of about 5-7.5cm (2-3 inches) is preferable; this could also work with a supply temperature just above 30°C (86°F).

Deliverer schrieb:

In my opinion, the most important thing is to install the underfloor heating BEFORE moving in. Since the subsidy is only available if you install a heat pump at the same time, it’s probably an unavoidable “bitter pill.” But if you don’t do it, the opportunity is gone and you’ll regret it for the next 40 years. You can read the phrase "Unfortunately not possible, we are already living here..." in every other heat pump thread.

Yes, we thought the same. There seems to be no way around it. Underfloor heating will be installed on the ground floor, and low-temperature radiators on the first and second floors. This combination should pay off...

And the photovoltaic system (the only investment that truly pays off, especially when combined with a heat pump) later on? No, the interest rates are still low. We’ll install it together with the new roof (a good photovoltaic system means a full roof) as soon as it’s financially feasible.

Benutzer200 schrieb:

An air-to-water heat pump combined with underfloor heating is a good idea. However, the windows are not great. If the top and bottom are well and properly insulated, you can achieve reasonable electricity consumption (based on my own experience last year, since my house will only get external thermal insulation this year).
Then have an engineering office calculate everything. Underfloor heating pipe spacing should be around 5–7.5cm (2–3 inches); with that, a supply temperature just above 30°C (86°F) could work.

So you mean that without photovoltaic panels, it definitely needs to be carefully calculated. According to your experience, it would likely show that it's economically justifiable. That sounds good, in my opinion. How much would such a calculation cost? Can a qualified energy consultant do this as well?