ᐅ KfW 70 energy standard with gas condensing boiler, solar water heating, and fireplace

Hello,

Which combination would you recommend?
KFW70 with gas condensing boiler + solar water heating + heat recovery + fireplace
or KFW55 with low-temperature heat pump + heat recovery + fireplace?
(Low-temperature heat pump Proxon), (Proxon Zimmermann ventilation).

The costs for the 55 standard are 12,000 Euros more expensive.
I will provide the U-values shortly.
But first: which makes more sense?

Regards

The U-values are the key factor... the type of heating mainly affects the calculation model.

Is the gas connection included? Otherwise, it’s about €9,500 (approximately $10,400) more expensive, not €12,000 (approximately $13,100).

It’s unclear what the chimney has to do with this.

Generally, depending on the changes to the building components, I would recommend gas. With an air-to-water heat pump, you don’t really save much later on consumption... even if you achieve an annual performance factor of 4, you pay 6.2 cents per kWh of heat—gas costs about 7 cents per kWh (these values always depend somewhat on the tariff). With an annual performance factor of 3, you pay 8.2 cents per kWh; the actual value for your annual performance factor will be somewhere in between.

I will provide the U-values within 2 hours. So, for the 12,000 (probably closer to 11,500), the gas connection has already been accounted for. Plus, there's the KfW 55 subsidy, so that's another 5,000 deducted. KfW 70 and 55 homes are built by Bien-Zenker. Would the low-level heat pump operate inefficiently without photovoltaic panels? According to Bien-Zenker, the chimney can distribute the warm air to all rooms. I'm just not sure, because some users consume around 3,000, but others can use up to 5,500, which would be pointless at 19 cents per kWh. The gas heating would consume about 7,000 to 8,500 kWh.

KfW 55
0.137 W/m²K
Window U-value: 0.5

And kfW70? To estimate, a few more values would be needed... and the geometry.

If you assume 7500 kWh, that equals annual heating costs of €525 using gas. Even with a 20% savings, it would take 109 years for this to pay off purely from heating costs; with a 50% savings (and even 20% is not certain), it would still be 43 years... this assumes that the kWh cost of an air-to-water heat pump is really the same as gas.
So it’s not worthwhile.

BeHaElJa schrieb:
If you assume 7500 kWh, that results in annual heating costs of €525 with gas. Even with a 20% saving, it would take 109 years for this to pay off based on heating costs alone; with a 50% saving (and even 20% is not certain), it would still be 43 years… assuming the kWh cost of an air-to-water heat pump is really the same as gas.
So it’s not worth it.

I completely agree with you.

The bank argued similarly to me.

Later, I recalculated this several times with a good friend: the standard COP 3.x air-to-water heat pump and the gas boiler perform almost the same (as of now). You save the gas connection, which costs money. However, the air-to-water heat pump is more expensive to operate. With a COP of 3 and electricity costs of $0.20 per kWh, the effective cost is about 6.66 cents per kWh. For that, I’d just buy my expensive gas.

Of course, this is a form of speculation: neither you nor I know the future price developments of energy sources.

Even though fossil fuels are currently cheap compared to past years, prices will rise again. One argument for gas is that reserves are still very large. The disadvantage: fossil fuel with associated CO2 emissions.

Electricity seems to have an advantage here. Currently, just over 33% of electricity in Germany is covered by wind, hydropower, and solar (notable for a country at this latitude!). However, transmission losses for electricity are quite high, the primary energy factor for gas is 1.1, while electricity’s is more than twice that.

Upgrading the grids (including direct current transmission lines, adjustments to local electricity networks, etc.) will be extremely expensive and is only just beginning. This will cost many, many billions before the measures are completed in around 25 years. These costs will be passed on to electricity prices. So I am almost certain: electricity will not get cheaper, but rather moderately more expensive. Here, infrastructure costs play a bigger role than generation costs.

At present, an air-to-water heat pump is certainly worth considering (especially environmentally). It also helps with KfW certification. But it does not save money. These units are expensive. You can get a gas condensing boiler practically thrown at you, and when one is worn out after 10–15 years, it’s easy to buy a new one. Also, I find it sensible to have a gas connection in the house – as there will be interesting technologies that will compete well with air-to-water heat pumps and others.

But: none of us can see the future… Let’s be surprised. We live today. In my opinion, the decision for or against an air-to-water heat pump or gas condensing boiler can be made according to personal preference nowadays; from today’s perspective, you can’t really make a wrong choice in either case.

Kind regards
Thorsten