ᐅ Is the heat pump too large when combined with a fireplace?

Hello, I have received a heating requirement of 8.8 kW from the heating installer based on the heat load calculation (KFW 55 standard, timber frame construction, fully installed underfloor heating, 170 sqm (1830 sq ft) living area). However, this calculation did not take into account that we are also planning a water-heated fireplace, which we will use daily in winter (wood is available free of charge), and intend to use it for both space heating and hot water production (a 200-liter (53-gallon) buffer tank is planned).

We have now received an offer for a ground source heat pump with a capacity of 10 kW. The question is, do you think this is oversized considering the supplemental heating from the fireplace? Would an 8 kW heat pump be sufficient?

The heat pump’s main operating time would be in the summer for hot water production (heating demand is generally lower in summer). In winter, most of the heat would come from the fireplace, and the heat pump would only activate when the buffer tank heated by the fireplace is depleted.

The fireplace has a water output of 5 kW and a direct heat output of 7 kW.

Thank you very much for your opinions!

Hello,

MeisterBob schrieb:
Hello, based on the heating load calculation (KfW 55, timber frame construction, underfloor heating throughout, 170 sqm (1,830 sq ft) living area) I received a demand of 8.8 kW from the heating installer.

Is a controlled ventilation system with or without heat recovery planned? Did the heating installer create this themselves, or does it come from a system partner?

MeisterBob schrieb:
...However, the calculation did not take into account that we have also planned a hydronic fireplace, which we will use daily in winter (wood is available free of charge) and intend to use for heating and hot water preparation (buffer tank 200 l (53 gallons) planned).

You have to differentiate here, for example, between KfW certifications (10% allowed) and reality! In practice, the credited share is usually somewhat higher, depending on the boundary conditions. Whether a 200 l (53 gallons) buffer is sufficient, I rather doubt, but it depends on the specific conditions! It seems no exact calculation exists ;-)
The higher the energy share of wood burning within the annual balance, the less worthwhile the relatively high investment in a brine-to-water heat pump!

MeisterBob schrieb:
...We have now been offered a brine-to-water heat pump with 10 kW capacity. The question is, do you find this oversized due to the fact that additional heating will be needed? Would an 8 kW unit also be sufficient?

It might be, but not necessarily! What happens if no one is able to fire the wood during illness? Then the brine heat pump will be the only source, and possibly overstrained, which can damage the ground source sustainably!
An important factor for brine heat pumps is the guaranteed and sustainable yield (capacity, energy) of the underground source. To assess this, the actual demand (capacity, energy) for heating and hot water needs to be known—how high are these?
Also, it is important to clearly separate the instantaneous capacity and the energy over the annual balance! ;-)
This combination is a compromise that probably does not represent a good overall economic case.

MeisterBob schrieb:
...The heat pump would mostly operate during summer for hot water production (less heating needed in summer). In winter, most heat would come from the fireplace, and the heat pump would only activate when the buffer charged by the fireplace is empty.

"Winter" and "summer" are not reliable energetic terms. From an energy perspective, only annual degree hours matter!
Example:

MeisterBob schrieb:
...The fireplace has a heat output of 5 kW hydronic and 7 kW direct output. Thanks for your opinions!

7 kW in the installation room can quickly become a significant problem. What is the heating load of this room?

Best regards