ᐅ Air-to-water heat pump combined with solar thermal and a wood-burning stove: costs, benefits, and practicality

Hello everyone,



Here are a few key points upfront:


We plan to build a single-family house with 121sqm (1300 sq ft) of living space this summer. Ground floor and upper floor, for 2 adults and 2 children.

The roof will face south.

We will use Ytong (30cm (12 inches)) blocks, with triple-glazed windows. Underfloor heating will be installed.

We live in Hesse, Rhine-Main area.


A air-to-water heat pump will be installed since we do not have gas and do not want to have any tanks for gas, oil, or pellets either inside the house or buried in the garden.

We would also like a fireplace for coziness and because we have almost free access to firewood. Solar thermal is also being considered; the question is whether it is worthwhile and if it should be used just for hot water or also for heating.

The following offer has already been presented to us:


A Nibe air-to-water heat pump split system with building heat load up to 7 kW, a buffer storage tank of 270l (71 gallons) with an additional 100l (26 gallons) buffer tank including Pedotherm underfloor heating.

For solar, 4sqm (43 sq ft) – 2 collectors and a 230l (61 gallons) buffer tank would be added.

The extra cost for solar is about 4000,- €.

For connecting a hydronic fireplace, including piping, pump, return lifting, and drainage protection, nearly 3000,- € is charged.

I am calculating about 3500,- € for a fireplace with an external chimney.

So, including the air-to-water heat pump, it would be over 10,000,- € for the fireplace and solar combined.

Regarding the questions:

The buffer storage tank seems very small for this project—is that accurate?

What makes sense for the heating system, considering it should pay off as much as possible? Because of the fireplace desire, it might not be possible, but well, the fireplace is a luxury and would be accepted even if it is not cost-effective.

I am concerned about only having an air-to-water heat pump in the cold season, due to electricity costs, and 7 kW building heat load seems low (though I have no expertise). A friend has an air-to-air heat pump and currently the electricity costs are extremely high.

What makes sense? What else should I include in the calculation, what might I have overlooked or should consider?

What do you think about Nibe?

Regards,


Max

Hi,

I’m afraid solar thermal systems won’t be cost-effective – not even over 10 to 15 years. In winter, you get hardly any sun, and in summer the air-to-water heat pump still performs reasonably well.
A fireplace only makes financial sense if the wood is free and you have enough of it. For us, it was too expensive just for coziness – we would have had to build a somewhat larger house to accommodate everything, plus the control system gets complicated, and experience shows it wouldn’t be used that often anyway.

Regarding electricity costs for an air-to-water heat pump – I wouldn’t install one on the Zugspitze or the Brocken (mountains with harsh climates), but near Main with its moderate temperatures, it looks quite different. Ultimately, it mainly depends on insulation and heating demand – the additional costs for a gas connection (30 meters (100 feet) to the street, 50 meters (165 feet) to the nearest gas main) were, at least in our case, the reason to go with the air-to-water heat pump.

Regards
I.

After careful consideration, we have also decided against solar thermal systems; for the construction project, the €4000 will be better invested elsewhere.

I am still uncertain about the layout of the buffer tank in relation to the fireplace, but since solar thermal is no longer an option, there might be a better alternative using the existing air-to-water heat pump and the current offer.

M.Mustermann schrieb:
For connecting a water-based fireplace, including pipes, pump, return flow lift, and drain protection, they charge nearly €3000.
I’m now estimating around €3500 for a fireplace with an external chimney.

You’ll need a larger buffer tank for the fireplace, plus the controls, maintenance, and so on.
How much more electricity will you need in winter for the air-to-water heat pump? €20–50? You’d have to heat for a long time before the wood pays off.

€3500 for a stove with an external chimney is tight. If you add a mechanical ventilation system with heat recovery and require a certified fireplace, it probably won’t work out.

Only up to 50 € in heating cost savings—do you mean per month or per year? I prefer to ask even if it sounds silly.

I can’t calculate it exactly, but if I assume an average savings of 35 € per month and 5 months per year, that amounts to 175 € annually. That means the cost of connecting to the heating system would be recovered after about 17 years. This calculation does not include wood or other fuel costs.

Please feel free to be brutally honest with me.

In my opinion, the budget you have set for the stove and external chimney will not be sufficient. I would estimate at least double, possibly more, especially since you plan to use the stove frequently. A decent continuous-burning stove is quite an investment.

Have you already consulted with a stove specialist for advice?

A radiant floor heating system is slow to respond compared to radiators. A water-circulated stove primarily heats the central heating system and is intended to relieve it. However, it heats the rooms less and is significantly more expensive to install than an air-independent stove without a water jacket. The latter would directly heat the rooms, probably to the extent that you’ll need to open the windows during the heating season because it gets too warm.

Unfortunately, I can’t tell you if the proposed air-to-water heat pump will be sufficient.
We will be heating with gas. Our trench is about 60 meters (200 feet) long. The cost for the gas connection is just under €2,000. We had the local civil engineer handle the trenching and laying of empty conduits together with the supply and disposal pipes. Everything is negotiable with the utility providers.
The house had to be connected anyway.

How are things with your telecommunications and water/sewage connections? Will everything need to follow the same route as the gas line...?
Unless gas is absolutely unavailable.