ᐅ Gas, heat pump, and solar energy for a single-family home?

Hello everyone,

We just had a conversation with the company responsible for our heating and plumbing installation.
First of all – we are building a large single-family house with a basement, two full floors, and a hipped roof with a 22° (22 degrees) pitch. Wall construction is 17.5 cm (7 inches) sand-lime brick, insulation with mineral wool, plus a brick façade.

We are building according to the 2012 Energy Saving Ordinance (EnEV 2012) and are not aiming to achieve a higher standard.
Our original plan was:

- Gas heating with underfloor heating on all levels, no wall-mounted radiators, and a central mechanical ventilation system with heat recovery.

Now, after the discussion, I’m totally confused. The company recommends:

- Heating via an air-to-air heat pump, solar thermal for hot water, plus gas to support hot water
- Underfloor heating only on the ground floor and first floor, excluding children’s rooms and bedrooms (to avoid overheating during sleep), with the rest heated by wall-mounted radiators on a second heating circuit
- No mechanical ventilation system with heat recovery due to noise issues

I can understand reconsidering the mechanical ventilation system because of potential constant noise and airflow, so we might want to think that over.

But I’ve never heard of combining a heat pump, gas, and solar thermal in one system!

Solar thermal is said to be uneconomical anyway, especially with a roof pitch of only 22° (22 degrees), right? We also don’t have a direct south-facing roof orientation. Does anyone have links or information about the economic viability?

Our main priorities are comfort; cost and economic efficiency are not the primary focus, but I don’t want to end up building something completely pointless either. The problem is, we need some sort of renewable energy source to comply with the Energy Saving Ordinance. The thermal protection report is not available yet, but I definitely need some concrete information for the next meeting. It would be great if someone could help!

From everything I have read and believe I understand, your idea of using a single heat generator with only one heating circuit (all underfloor heating) is the better option. Definitely have a heat load calculation (HLB) done according to DIN EN 12831, preferably conducted independently from the house builder/general contractor, and base the underfloor heating design on that. This way, you can at least create small temperature differences between rooms.

Thin duvets and adjusting to comfortable temperatures in the bedroom are likely unavoidable nowadays without air conditioning in the bedroom.

With heat pumps, solar thermal systems, AND gas, it’s mostly the installer who profits...
No, that actually doesn’t make much sense.
Concerns about mechanical ventilation with heat recovery and airflow noise are generally unfounded if a properly installed central mechanical ventilation system is used.

Hello,

Panama17 schrieb:

- Heating via (air-to-air) heat pump, solar for hot water, plus gas to support hot water
- Underfloor heating only on the ground floor and first floor, excluding children’s rooms and bedrooms (to avoid overheating during sleep); the rest heated with wall-mounted radiators using a second heating circuit
- No mechanical ventilation system due to noise concerns

An air-to-air heat pump only makes sense in a passive house; otherwise, in my opinion, it's just wasted money! I also don’t understand adding a second heating circuit to an existing system. You definitely shouldn’t skip ventilation—you can’t reliably ensure the necessary ventilation intervals during the first two years manually! Whether the ventilation is central or decentralized doesn’t matter.

However, if you want to stick to your original plan, you won’t avoid installing a solar system for domestic hot water unless you instead increase the insulation according to the 15% rule. If the goal is KfW 70, then with gas as the heat source, in my opinion, a mechanical ventilation system with heat recovery will be absolutely necessary.

So, I would definitely decline the heating contractor’s offer, thank you very much.

Regards, Bauexperte

Hi Bauexperte,
could you please help me out again? I’m really confused. Everyone says something different, and the texts about the Energy Saving Ordinance online are too complicated for me as a layperson.

How exactly does the Energy Saving Ordinance work? We have already submitted the building permit / planning permission application and explicitly do not want to build according to the latest Energy Saving Ordinance; which version applies to us then? The 2009 Energy Saving Ordinance? Or is there an intermediate version from 2012 or 2014?

We don’t have a general contractor; we are building with an architect. The problem is that the “advisors” are family members, very experienced in construction, but all over 60 years old, so I don’t think they are really up to date with the latest technology. Heating and plumbing will most likely be handled by my uncle’s company.

I’ll summarize the statements from our conversation:

“Heating only with gas won’t work; a heat pump will probably be required by the thermal protection report. A heat pump alone is not enough, though; during transitional periods and cold winters, you need gas to cover peak demand. Solar thermal systems take care of hot water in summer completely, saving a lot of electricity, which pays off in a few years.”

“For the bathrooms, in addition to underfloor heating, we should install a towel warmer, connected to a second heating circuit so it can be switched on quickly. We advise against an electric towel warmer (I didn’t ask why).”

“In the bedroom, underfloor heating is too warm. Actually, no heating is needed if you want around 18°C (64°F) for sleeping. During transitional periods or very cold winters, a wall-mounted radiator makes sense for quickly warming the room when needed.”

“We should reconsider underfloor heating in the children’s rooms. They should have about 22°C (72°F) during the day, and underfloor heating (and the screed) takes 4-5 hours to cool down to a comfortable sleeping temperature.”

The basement won’t be purely for storage but won’t be used permanently as living space either (playroom for the kids, gym, hobby room).
“Keeping the basement heated year-round to about 18°C (64°F) with underfloor heating consumes a lot of energy. If the kids want to use the basement spontaneously in the afternoon, it takes a long time to warm up with underfloor heating; a wall-mounted radiator heats the room faster.”

“A mechanical ventilation system with heat recovery is only necessary if the building is constructed too quickly. If you observe normal drying times (construction period 12 months), special ventilation is not needed to avoid mold, because moisture will have evaporated by then.”

To be honest, I feel like all of these statements are complete nonsense. But as a “young lady” sitting in front of three men over 60, I really need solid arguments and can’t just say “I read that in the forum.” I’m already being told not to read so much on the internet.

@Bauexperte
What is the 15% rule? We don’t want to reach KfW 70 standard, only the bare minimum required by the Energy Saving Ordinance. Do you perhaps have some resources for me where I can understand the economics of heat pumps and solar thermal systems as a layperson? Could you also give me good arguments why having two separate heating circuits makes no sense?

@oleda222
What is an HLB according to DIN xy?

Thanks to everyone, I really feel so helpless right now!!!!!

Good evening,

Panama17 schrieb:

How exactly does the energy saving regulation work again? We have already submitted the building permit / planning permission and explicitly do NOT want to build according to the latest energy saving regulation. Which one applies to us then? The 2009 energy saving regulation? Or was there an intermediate version in 2012 or 2014??

The energy saving regulation that was valid at the time of your building permit / planning permission submission applies to you. That should have been the 2009 version, if I remember correctly.

Panama17 schrieb:

"Heating only with gas will not be possible; a heat pump will probably be required by the thermal insulation report. A heat pump alone is not enough; during transition periods and cold winters, gas is needed to cover peak demand. Solar thermal energy entirely covers hot water heating in summer, saving a lot of electricity, so it pays off within a few years."

If only the 2009 energy saving regulation has to be met—that is, if a KfW 85 efficiency house is to be built—a gas condensing boiler is sufficient. However, since the Renewable Energies Heat Act 2009 must also be complied with, a 15% share of renewable energy must be installed, for example solar hot water heating. The energy saving regulation has required home builders to use renewable energy for several years now. If you want to avoid solar collectors on your roof, you can alternatively compensate with insulation that is 15% better.

The Renewable Energies Heat Act states:

**VII. Measures to Save Energy 1. Measures to save energy only count as substitution measures under § 7 paragraph 1 number 2 if, during the construction of buildings, a) the respective maximum annual primary energy demand value and b) the specific thermal insulation requirements for the building envelope according to the energy saving regulation in its currently valid version are reduced by at least 15 percent.

Panama17 schrieb:

"For the bathrooms, in addition to underfloor heating, we should install a towel warmer that runs on a separate heating circuit so it can be quickly switched on. We advise against an electric towel warmer (didn’t ask why)."

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Panama17 schrieb:

A towel radiator, as the name suggests, only keeps towels warm—nothing more; these are usually powered by electricity. What the gentleman probably means is a regular bathroom radiator in a bar design; quite attractive with a gas heating system.

Panama17 schrieb:

"The bedroom gets too warm with underfloor heating. Actually, you don’t need heating there if you want around 18°C (64°F) for sleeping. But during transitional periods or very cold winters, a wall-mounted radiator makes sense to quickly warm the room when needed."

Has it not occurred to him that the surrounding rooms need to heat the then cold bedroom too? Or that constant exposure to cold drafts is bad for the joints?

Sleeping constantly in a cold room is unhealthy! Well, fresh air fans might enjoy sex even at 15°C (59°F) – or rather prefer a heated room? A car would also be more comfortable, I think.

Panama17 schrieb:

"We should reconsider underfloor heating in the children’s rooms. During the day it should be around 22°C (72°F), and underfloor heating (including the screed) takes 4-5 hours to cool down to a comfortable sleeping temperature."

At 22°C (72°F) with underfloor heating, your kids would practically evaporate.

Of course, underfloor heating always reacts slower than radiators, but not as slowly as these gentlemen seem to remember. Never change a running system! It regulates itself through individual room control and solar gain through windows.

Panama17 schrieb:

The basement will not be just a utility cellar but won’t be used permanently as living space either (playroom for the kids, gym, hobby room).
"Heating the basement year-round to about 18°C (64°F) with underfloor heating consumes a lot of energy. If the kids want to go downstairs spontaneously in the afternoon, underfloor heating takes a long time to warm up; a wall-mounted radiator heats the room faster."

Yum, yum... The decor will smell nice when radiators in the otherwise unheated basement are switched on "only" as needed.

If the basement has at least 12 cm (5 inches) of external insulation, I would install low-temperature radiators and run them continuously, set somewhere around 16°C (61°F). They also respond to individual room control and only turn on when needed. So no high costs. It only gets expensive if they are switched on and off constantly. However, these radiators are expensive, so underfloor heating almost pays off in comparison.

Panama17 schrieb:

"A controlled mechanical ventilation system is only needed if the construction is done too quickly. If normal drying times (construction time about 12 months) are observed, special ventilation is not necessary because the moisture will escape naturally and no mold will occur."

Are you building without water? Over 12 months? Are you leaving the shell structure over winter—from November to March? These times are long gone; name me a builder who understands previous (correct) procedures. Just be patient.

Panama17 schrieb:

I personally feel that all these statements are complete nonsense. But as a "young woman" sitting opposite three men over 60, I need solid arguments and can’t just say "I read this on a forum".

Cut them some slack; they have worked that way their whole lives. I believe they really mean well with you.

Panama17 schrieb:

I already keep being told not to read so much on the internet.

I can totally relate to that.

Panama17 schrieb:

@Bauexperte
What is the 15% rule? We don’t want to achieve KfW 70, just the minimum required by the energy saving regulation.

See above.

Panama17 schrieb:

Can you give me good arguments why two heating circuits are nonsense?

They operate at completely different temperatures!

Source: ** Laws online

Best regards, Bauexperte