German forum about plant engineering for home: heating system, solar energy, etc ?

131 posts in this topic

I think the most overlooked aspect of building energy efficiency is airtightness. You can put 200mm of external insulation all over a house but if it's draughty and air can easily move from inside to outside and vice versa, your expensive insulation will just be largely bypassed.

 

The main focus for me would also be on improving the energy efficiency of the building rather than focusing on the heat source. Once you drive the energy requirement down to a minimum, you can look at suitable heating options. Remember, gas boilers and even heat pumps won't typically outlive you. You will need to replace them again. I can imagine that gas will be banned even in retrofits in the next decade. This war is only going to accelerate legislation that outlaws gas boilers in new builds. In retrospect we should have banned gas boilers in all new builds at least a decade ago, if not more. The 2009 EnV should have outlawed them IMO. There was no good reason to allow continued installation of gas heating in new builds at that stage. But we are where we are. Once new build gas installations are banned, retrofits will surely follow, especially in houses (apartments are much more difficult so may have an derogation for a number of years).

 

Given the fact you may well be forced to go to a heat pump at your next change of heating system, you should focus on driving down the energy requirement of the property as your top priority. It will eventually be self financing if you borrow for it.

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But AFAIK a heat pump does not make sense if you do not have heated floors, and retrofitting heated floors is damn expensive.   Which other viable alternative exist?

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4 minutes ago, Krieg said:

But AFAIK a heat pump does not make sense if you do not have heated floors, and retrofitting heated floors is damn expensive.

Yes, unfortunately true.

But biggest point is still insulation. Not to improve the insulation of a 1994 100kWh/m2 house is a bad decision, also financially, also if you need to borrow extra.

 

BTW do I remember correctly that gas heating is already banned for new built from 2030?

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4 minutes ago, Gambatte said:

BTW do I remember correctly that gas heating is already banned for new built from 2030?

 

That I don't know, but the second energy relief package for the current crisis includes Energy 55 mandatory from new buildings from next year, and 65% of energy used for heating must be from renewable sources from 2024.

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1 hour ago, Krieg said:

But AFAIK a heat pump does not make sense if you do not have heated floors, and retrofitting heated floors is damn expensive.   Which other viable alternative exist?

A heat pump makes most (financial) sense where a relatively low flow temperature can still produce a comfortable environment. Typically this means the heating surfaces need to be fairly large to compensate for the low temperature they operate at. The most well known option is under floor heating but there are alternatives. UFH works mostly through radiation. This means you can flip actually install those plastic pipes in the ceiling or walls and the same effect will be achieved, in fact ceiling heat is more effective as it isn't blocked by furniture and it's a very nice warmth as it hits your body from above. Ceiling heat may be retrospectively installed in certain circumstances and installing it instead of UFH would mean doors and floors could be left as they are (no new doors, door frames, carpets, tiling etc.).

 

I've got UFH and it's great but there are alternatives to consider. Here's a marketing blurb from a ceiling heat system supplier (so take the harsh criticism of UFH with a pinch of salt):

https://www.beka-klima.de/fileadmin/beka/pdf/div/beka_deckenheizung-vs-fussbodenheizung.pdf

 

There are also simply "oversized" radiators, but how effective they are I am not sure. They were originally specified for our basement but I decided against and opted for UFH there too, so I have no experience of them.

 

I strongly suspect that regardless of cost, gas boilers will be banned in houses in the next decade, certainly in new builds. I was forced, for example, when replacing the last gas boiler in my Berlin rental apartment, to install a condensing boiler, despite the previous boiler being a simple non-condensing type. This resulted in significant extra expense as a new stainless steel flue needed to be installed up to chimney stack level. Thankfully the apartment is on the top floor, otherwise it would have been much worse. I was not allowed to install a like-for-like replacement boiler and I suspect the law will in the not too distant future outlaw all gas boilers in houses when it comes time to replace the heating system. The OP will then face the same problem. It's better to tackle the energy inefficiency problem head on now and fix that first. It also gives more time for a payoff of the investment. It gives options then with the heat source too. If the OP doesn't tackle heat loss through poor insulation and airtightness, he will be compelled to stick with gas or some other high flow temperature heating system.

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1 hour ago, Gambatte said:

But biggest point is still insulation. Not to improve the insulation of a 1994 100kWh/m2 house is a bad decision, also financially, also if you need to borrow extra.

Yep, definitely. We have a 212m² house and used 6000kWh last year for everything, heat, hot water and electricity (we've got no gas, only the heat pump). If we had 100Kwh/m² we'd be spending almost 4 times as much on energy as we do, so instead of €150 a month we'd be spending ca. €550. At that sort of difference (and that's before our electricity price guarantee expires-the current prices are much higher) we'd easily be able to justify borrowing for an insulation and airtightness retrofit.

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5 minutes ago, Krieg said:

But AFAIK a heat pump does not make sense if you do not have heated floors, and retrofitting heated floors is damn expensive.   Which other viable alternative exist?

A week ago I saw a new report (and can't find a link at the moment sadly) which suggested heat pumps "could" work with existing radiators (although the oversized radiators mentioned by @murphaph would be preferred), but there is no denying that they will struggle to provide anywhere near the sort of heat a gas boiler can get into the water. That's why I think many people (or at least me!) will need to consider a mixture of solutions for retrofitting.

I still like the idea of infrared heating too, if you have a traditional house (where the cabling could be channelled and replastered), but again, that prefers a well insulated house, with limited temperature variation between indoors and outside, and how green it is depends upon how you obtain your electricity.

Another interesting option is a fuel cell. Whilst these typically run off natural gas, the amount used is fraction of that which would be necessary for a gas boiler, and they are considered a "green" solution (they can run off methane, which would be an even greener solution) and as such subsidies are available. You need to have a room with at least 6m2 for the fuel cell to sit.

 

  

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Personally I wouldn't hook up an expensive new heat pump to an existing and almost certainly corroded system. I'd install all new plastic piping and those oversized aluminium radiators (which are actually convector heaters and thus poorly named!) if I had no other options available (buried UFH or ceiling or even wall heat would all be preferable to large radiators IMO)

 

Edit: yeah there are other interesting alternatives available like IR, but only if you can get the heat requirement down to a manageable level (at current gas prices), otherwise those systems are far too expensive, when compared to the the current price of gas....but where is the price of gas heading? At least with electricity we have some flexibility in how we produce it. We can produce all of it domestically if push comes to shove (literally the nuclear option), though hopefully a broad enough mix of renewables across an integrated EU energy market, will mean there's always enough base load generation without fossil fuels or nuclear fission.

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2 minutes ago, murphaph said:

Yep, definitely. We have a 212m² house and used 6000kWh last year for everything, heat, hot water and electricity (we've got no gas, only the heat pump). If we had 100Kwh/m² we'd be spending almost 4 times as much on energy as we do, so instead of €150 a month we'd be spending ca. €550. At that sort of difference (and that's before our electricity price guarantee expires-the current prices are much higher) we'd easily be able to justify borrowing for an insulation and airtightness retrofit.

 

First of all thanks to you all for your opinions.

 

Retrofitting floor heating is out of discussion like unfortunately many other big improvements due to the cost. By the way the costs of all this in Munich area will be way higher than the rest of Germany. I realized this by reading forum (that finally I found) where people where asking opinion about offers they received...difference sometime is HUGE from Land to Land.

In order to secure this property we are already in the last-gasp effort in term of financial effort (equity but also mortgage). we want to keep a safe buffer of money in case shit will happen. The only next debt we are willing, MAYBE, to take is just around 8K euro for covering the remaining part of money we need to buy a car more appropriate for a family (and for tall people like me :P...now I looks like an elephant in an old FIAT 500 ). The rest of the cash we will need for some minor (?) adjustment we need before entering the house and for the mandatory heating system replacement.

By the way, as mentioned in the first post, I was not thinking to a normal gas boiler but condensed one in an hybrid setup paired with solar thermal.

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Yeah you can't even install non-condensing boilers any more. It has to be condensing. Try to consider that a lot of insulation and airtightness work can be carried out by the home owner if they are someway competent. Fixing external insulation for example can in some cases be very straightforward. You then engage a plasterer to plaster the stuff you fitted. I know two competent DIYers around here that fitted their own external insulation and just had the plasterer do the final work. I guess it all depends on your skill level. Fitting a gas boiler is not a DIY task no matter how competent you are. There's little money to be saved by doing part of the work yourself. But you know your personal circumstances best of course and I can understand your position. I would steer clear of the Bauexpertenforum anyway: they hate DIYers asking questions IMO. There's the Haustechnik forum, which I always found more welcoming.

 

Can I ask, why is a change of heating system compulsory at all? I missed that bit.

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17 minutes ago, murphaph said:

 I guess it all depends on your skill level.

 

Near zero. I can just bring brute force to the cause :D

I am not that handy man unfortunately... i can just assemble ikea fornitures and mount ceiling lamp (with the terror of boring the ceiling in place where i should not)

 

17 minutes ago, murphaph said:

Can I ask, why is a change of heating system compulsory at all? I missed that bit.

 

End of life of the existing oil heater in less than 2 years.

I want to do it now before entering home and for taking chance of the gov subsidies. In my case the total of them should be 40%.

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ah, I forgot to mention. According to the last 3 year bill (oil refilling service) of the owners (a 40ers couple, i guess without children) they were paying an average of 105 euro per months...we are talking about heating and hot water.... definitively less of what we pay now for our 70 sqm flat in Munich. And we don't use a lot heaters because the flat tend to remain warms. I am figuring out why i pay so much here.

 

 

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23 minutes ago, Frantic said:

End of life of the existing oil heater in less than 2 years.

I want to do it now before entering home and for taking chance of the gov subsidies. In my case the total of them should be 40%.

 

How do you know this?  We moved to our house 13 years ago and the heater was already old, since then we planned to change to gas and kept some money in case the boiler breaks, however it has been working strong with minimum maintenance.     The reason we have waited so long is that heating oil prices were extremely cheap in the past, so we felt like we had to pay 12k-15k for the privilege of paying more in heating.

 

12 minutes ago, Frantic said:

ah, I forgot to mention. According to the last 3 year bill (oil refilling service) of the owners (a 40ers couple, i guess without children) they were paying an average of 105 euro per months...we are talking about heating and hot water... definitively less of what we pay now for our 70 sqm flat in Munich. And we don't use a lot heaters because the flat tend to remain warms. I am figuring out why i pay so much here.

 

 

 

This sounds OK.  We (family of four) live in a 129 m2 house plus cellar (which is partially heated) and we pay something around 1100 - 1600 EUR per year in heating oil.  And we have to keep the house really warm during winter because my wife comes from a tropical country and she is complaining about the temperature all the time.  And everyone except me takes long showers at scalding temperatures.   If I had to refill my tanks right now with the current crazy prices I would pay something around 2200 EUR, which is not good but not extremely bad considering the situation.

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@Frantic, you are serious on solarthermie but say improving insulation is not in the budget. With respect, I think insulation improvement is a much better investement than solarthermie.

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7 minutes ago, Gambatte said:

@Frantic, you are serious on solarthermie but say improving insulation is not in the budget. With respect, I think insulation improvement is a much better investement than solarthermie.

So do I. Solar thermal produces little hot water in winter and way too much in summer. I wouldn't voluntarily add it anywhere. And it's not maintenance free either.

 

I would also really question the assumption that the heating system is on its last legs. Who said this? You should maybe get a second opinion. I am guessing as you concede to having no DIY skills, that a third party told you the system would not last much longer.

 

Oil burners can last a very, very long time.

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Didn't he write it's a legal requirement to replace the old kerosene heating?

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On 4/5/2022, 10:16:36, Frantic said:

my situation is that I found a house I like and in case of purchase I will need to change the existing oil heating.

 

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15 minutes ago, Gambatte said:

Didn't he write it's a legal requirement to replace the old kerosene heating?

Ah I missed that if he did. It's a new one on me if you can be forced to replace an existing, functioning installation in your own home, Bestandsschutz and all that stuff. I've never heard of it anyway, maybe some local ordnance?

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1 hour ago, murphaph said:

Oil burners can last a very, very long time.

 

Also my experience too, but regarding gas boilers. Was told when I bought an old house, you need to replace the boiler which was already 15 years old. Sure it broke down eventually, but was trivial and cheap to have fixed. It was regularly serviced, so carried on working fine. After maybe 7 years, due to extending the building, a larger capacity one was needed, so was replaced by a modern combi boiler and the old water tank removed.

 

You might be surprised how long 'old' things actually last.

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On 05/04/2022, 12:31:05, dstanners said:

I'm considering a ground source heat pump, plus PV, plus a wood burning stove...and possibly a wind turbine.

 

Are you even allowed to have a wind turbine as a private house owner?

Certainly where I live, you need to tie things down to stop them blowing away.

It's been windy outside all day. Currently 42 km/h according to the hourly weather, but it's often over 30 as this place is quite exposed.

 

Has anyone actually any real experience with one of these?

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