ᐅ Hybrid heating system: Is combining a heat pump with a gas condensing boiler a practical solution for renovating older homes?
Created on: 19 Mar 2022 08:25
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taskyyy
Hello everyone,
In a detached house with an attached garage and 145 m² (1560 ft²) of living space, there is still an oil heating system installed, which now needs to be replaced.
Does it even make sense to install a heat pump combined with gas in an old building with poor insulation? Or would it be more practical to just install a gas boiler? Will the heat pump actually "kick in"? Or will the gas boiler always be the only active unit?
The advantage of the combination would be the higher subsidy. A subsidy for gas is only possible if solar thermal is installed, but that doesn’t seem very practical, right?
Does anyone have experience with this combination? What would you recommend? Or would it be better to first fully insulate and then simply install a heat pump?
The energy consultant I had, who is also certified by KFW, seemed totally unsure. Maybe someone here has a rough idea?
In a detached house with an attached garage and 145 m² (1560 ft²) of living space, there is still an oil heating system installed, which now needs to be replaced.
- The heating load is approximately 15 kW.
- The façade has a U-value of 0.97 W/m²K and double-glazed thermal insulation windows are installed.
- The roof is insulated.
- The top floor ceiling is insulated with 10 cm (4 inches) of mineral wool.
- Moreover, the house is fully basemented and the basement ceiling is insulated.
Does it even make sense to install a heat pump combined with gas in an old building with poor insulation? Or would it be more practical to just install a gas boiler? Will the heat pump actually "kick in"? Or will the gas boiler always be the only active unit?
The advantage of the combination would be the higher subsidy. A subsidy for gas is only possible if solar thermal is installed, but that doesn’t seem very practical, right?
Does anyone have experience with this combination? What would you recommend? Or would it be better to first fully insulate and then simply install a heat pump?
The energy consultant I had, who is also certified by KFW, seemed totally unsure. Maybe someone here has a rough idea?
D
Deliverer19 Mar 2022 19:58WilderSueden schrieb:
With a high heating demand and high supply temperature, the efficiency of a heat pump is simply poor. The heating demand is completely independent of the type of heating system.
High supply temperatures are less efficient for heat pumps than lower ones. How to reduce these temperatures is exactly what we are discussing here in this thread.
The rest of your post... In winter, there is a lot of wind; heating with a heat pump is still better than oil heating, even when powered by coal-generated electricity. If we want to survive, we’d better put in some effort. But what am I saying – gas is currently phasing out on its own, so we can actually thank the old Russian for shaking things up here. ;-)
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WilderSueden19 Mar 2022 21:30That’s correct, the heating load is independent of the heating system. However, the costs of different energy sources vary. Gas will certainly not settle back at 7 cents/kWh, but electricity won’t stay at 30 cents either. Still, gas will remain significantly cheaper than electricity in the long term because it’s needed to fill the gaps between solar and wind power and, partly due to the nuclear phase-out, also to cover the base load.
I don’t see gas becoming obsolete anytime soon. We are simply replacing cheap pipeline gas from the Russian dictator with liquefied natural gas from the Gulf states and fracked gas from the US. That is unlikely to change for the time being. Many existing buildings can only be retrofitted with heat pumps at great expense (I currently live in one myself), and even if everyone wanted to switch, there simply aren’t enough skilled workers available.
I don’t see gas becoming obsolete anytime soon. We are simply replacing cheap pipeline gas from the Russian dictator with liquefied natural gas from the Gulf states and fracked gas from the US. That is unlikely to change for the time being. Many existing buildings can only be retrofitted with heat pumps at great expense (I currently live in one myself), and even if everyone wanted to switch, there simply aren’t enough skilled workers available.
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Deliverer19 Mar 2022 22:49The important thing – and it seems we agree on this – is that we get started.
Unfortunately, the current owner cannot provide the exact heating load. I can only estimate it based on the available data.
She still has the old radiator heating system. In January and February, the heating was set to level 3, and it was already quite warm. The heating unit is a Bruderus Logana G 105 from 1988, energy class D.
So, to summarize, it seems best to consult an energy advisor, insulate the facade and roof, install triple-glazed windows, lay underfloor heating both upstairs and downstairs, and then a heat pump would definitely make sense, right?
She still has the old radiator heating system. In January and February, the heating was set to level 3, and it was already quite warm. The heating unit is a Bruderus Logana G 105 from 1988, energy class D.
So, to summarize, it seems best to consult an energy advisor, insulate the facade and roof, install triple-glazed windows, lay underfloor heating both upstairs and downstairs, and then a heat pump would definitely make sense, right?
D
Deliverer20 Mar 2022 09:40It can be effective even with less extensive measures—just as you described, it would be perfect. (Maybe add photovoltaic panels to the roof if it’s going to be covered anyway.)
WilderSueden schrieb:
Predictions are difficult, especially when they concern the future 😉
So I’m simply approaching this with as few assumptions as possible, following Taleb and Occam’s principle. In winter, the sun shines little and stays low, so photovoltaic systems are not a reliable option. Additionally, here in the south, we often experience fog and sometimes go two weeks in winter without a single ray of sunshine. There is sometimes wind, but it often comes in storms, which is also problematic. Therefore, the electricity would have to come from the windy north, but the power lines there face opposition from citizen initiatives in every other village. Wind turbines face similar resistance. What else is left?
Nuclear power is being phased out, hydropower is considered "renewable," but today you won’t get approval to flood an Alpine valley in an environmentally friendly way. German geography doesn’t offer much anyway, even if you wanted to.
Fundamentally, there’s also the problem that unreliable energy sources like solar and wind must be massively oversized (which is expensive and not very ecological) to ensure supply in unfavorable conditions. Even with grid-level storage (also costly).
In the end, only coal, gas, and buying electricity from neighbors remain. Everything else relies on miracle technology. Expert opinions are nice, but healthy skepticism is also important. As long as it’s only the healthy skepticism of laypeople without expertise, that’s fine. There are entire institutes dedicated to this topic—they should know best.
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