ᐅ Gas Condensing Boiler or Air-to-Water Heat Pump for a Water-Heating Fireplace?

We are currently planning a new build of about 180m² (1,938 sq ft) to KfW70 standard and have been considering for some time which primary energy source to use. The plan definitely includes
- underfloor heating throughout
- controlled mechanical ventilation (current favorite: Buderus HRV)
- a water-based fireplace (Wodtke Giro, 8 kW with buffer storage)

Since we enjoy wood heat, it’s not a problem to cover cold peaks in winter, which can be expensive with a heat pump. However, a heat pump requires a higher initial investment by several thousand, and electricity tariffs for heat pumps are disappearing. At 27 cents per kWh, electricity is not cheap.

On the other hand, we would have to pay about €1800 (approximately $1950) just to install a gas connection (despite being in a new development area), plus a basic fee on the otherwise cheap gas, and an additional chimney flue running through the entire house would need to be planned and installed.

At the moment, we are undecided... My brother-in-law is a heating engineer and doesn’t want to influence us (though he would lean towards gas) and he works at Buderus, so we get very good discounts regardless of what we choose. That means the brand is basically set.

Is a Buderus heat pump (indoor or split system) a good choice together with the Buderus HRV mechanical ventilation? Or would gas be better?

Hello,

FrankDr schrieb:
......
- Underfloor heating everywhere
- Controlled mechanical ventilation (current favorite: Buderus HRV)
- Hydronic fireplace (Wodtke Giro, 8kW (27,000 BTU) with buffer storage)...

As in all other cases, a basic assessment must first be carried out — actual demand (capacity, energy) for heating and hot water. Only then can reliable conclusions be drawn and a suitable concept be found. Until then, everything is just assumptions and guesses without background!

FrankDr schrieb:
.... Since we like wood heat, it is not a problem to buffer cold peaks in winter, which are expensive with heat pumps.

With well-planned air-source heat pump systems, the occasional few hours/days of lower outside temperatures usually play little role, depending on location and energy demand.
Example:

In my planning, I always take local climate parameters into account!

FrankDr schrieb:
..... Still, a heat pump costs a few thousand more to purchase, and heat pump tariffs from electricity providers disappear… And at 27 cents/kWh, it’s not cheap…

Condensing gas boilers plus connection costs often come close to the price of a suitable air-source heat pump. With gas, you generally need a second heat generator to meet energy saving regulations (EnEV/KfW or EEWG). A heat pump can provide cooling; gas cannot!

FrankDr schrieb:
.... That means the brand is basically fixed…

And what if the devices hardly or not at all match the specific requirements? What is the discount really worth then?
Wood only makes sense if it is available free of charge on a permanent basis. Then one should be consistent, e.g., use a wood gasifier.
With hydronic fireplaces, the airflow capacity often poses a problem in new builds (overheating of the installation room). It is often forgotten that manufacturers’ performance figures apply only to defined operating conditions.
The ideal state is approached when only as much energy is generated or supplied as currently needed! The more components involved in heat generation, the more complex, prone to faults, and uneconomical (costs, energy efficiency) it becomes, due to partly competing requirements. Simply the best!
If thermal energy must be stored, efficiency usually decreases!

Best regards

€uro schrieb:


Gas condensing boiler + connection often compete directly with a suitable air-source heat pump. With gas, you usually need a second heat generator to meet the energy-saving ordinance/KfW or EEWG requirements. You can use a heat pump for cooling, but not gas!

Since we won’t be installing ground probes or anything similar, cooling won’t really be possible for us. The garden has multiple terraces, etc.
However, as far as I know, there is a more affordable—though less efficient—solution where you lay a kind of “water loop” around the house. I don’t know enough about that yet.

€uro schrieb:

And what if the appliances hardly or do not at all match the specific requirements? What is the discount really worth then?

I honestly can’t imagine that the savings effect would be so large with another manufacturer that it outweighs the discount for me. I get all heating elements (starting from the fireplace through heat pump/gas condensing boiler, all pipes, etc.) at a 30-40% discount plus installation at cost price. But only with Buderus, because he works directly there—and that’s certainly not a cheap brand.
I also included a question about which of the models available there would be interesting.

€uro schrieb:

Wood usually only makes sense if it is permanently available for free. In that case, you should be consistent—for example, a wood gasifier stove.

The wood stove is mainly for the cozy atmosphere. It doesn’t necessarily need to be cost-effective. I enjoy putting wood in and watching the fire.

€uro schrieb:

With water-jacketed fireplaces in new builds, the air-side output often causes problems (overheating of the installation room). People tend to forget that the manufacturer’s performance ratings only apply to a defined operating point.
You get closest to the ideal state by producing or providing only as much energy as is currently needed! The more components involved in heat generation, the more complex, prone to faults, and uneconomical (costs, energy efficiency) it becomes due to partially competing requirements. Simply the best!

Exactly for this reason we chose a water-jacketed fireplace. With these, up to 70% of the heat goes into the buffer tank and doesn’t dissipate, because otherwise, after just 30 minutes you would constantly have to open the windows due to overheating of the room.
This way, instead of just heating the living and dining rooms with the fireplace, I can heat the entire house (via water and underfloor heating).
I understand that the combination has to make sense. That’s why I’m asking whether the Buderus models mentioned above are suitable or if, for my chosen water-jacketed stove setup, gas or a heat pump would be better.

€uro schrieb:

If energy has to be stored thermally, it is usually inefficient!

Best regards.

Obviously. But with my firm decision to have a stove, I still believe this is the best solution.

Too bad, no more tips on the question of whether to choose gas or a heat pump with current prices?

Gas is definitely gas... with today's electricity prices, heat pumps only make financial sense in passive houses....

Good evening,

Mycraft schrieb:
Definitely gas... with today’s electricity prices, heat pumps only really make sense in passive houses...

If you are talking about an air-to-air heat pump, I fully agree with you. However, if you mean an air-to-water heat pump, you should reconsider your statement. Basically, neither option can be universally recommended or ruled out. Each construction project must be evaluated individually based on actual numbers.

Therefore, the original poster’s question—without reliable data and putting aside the usefulness of a water-bearing fireplace—cannot be answered.

Regards, Bauexperte