Heating costs for the new building with many windows

Hello forum,

we are planning to install many large windows in our new building (approx. 300sqm ground floor + upper floor). The southwest side will consist of 80-90% glass (window front ground floor + large windows upper floor). We also have many windows on the north side (but no window front).

Acquaintances are now advising us to reduce the size of many windows because there will supposedly be heat loss (winter) and high heating costs.

I am not really familiar with this yet - I am currently reading up on the topic of heat coefficient etc. But with a well-insulated new building, triple glazing, heat pump, photovoltaic system, I thought the heating costs would be manageable and not get out of hand.

I would appreciate your opinion and experience. How do you see it? What do you think? (Many large windows were actually important to us because of light, view, etc.).

Thank you for your help and advice.

Best regards

I wouldn’t be as worried about the heat losses as about the heat gains in summer. So it’s better to ensure good shading options (Raffstore). But yes, even a good modern window only protects against heat loss half as well (or even less) as average, standard-compliant masonry (+WDVS)/timber frame panel wall (0.6 vs 0.24 W/m²K). Additional disadvantages of window fronts: - Restrictions on furniture arrangement. - If you can look out, people can also look in from outside... - Does not protect as well against noise (or special soundproof glass is needed, which in turn protects less against heat loss or, if both are needed, is very expensive) - Does not protect as well against burglars - Does not protect as well against flying debris during storms - Usually looks only half as good as one imagined during planning. Smaller but well and sensibly placed windows can achieve the same advantages, sometimes even set nice accents in the interior and can be practically integrated into a normal living household (which is after all not a showroom or catalog photo motif).

But with a well-insulated new building, triple glazing, heat pump, photovoltaic system

The only influence on energy consumption is the insulation. And windows simply insulate significantly worse. But they also let heat in – just like today, when my heating was off almost all day. So please remember shading for the summer. Apart from that, I consider the question about heating costs for a house that will cost seven figures unnecessary. Whether the heating costs increase by €25 per month now is negligible. That is the order of magnitude we are talking about. P.S. For such a special house with a lot of glass, external professional heating planning is essential. Then you will have a well-functioning house in winter.

I have always liked large window areas and of course there have always been the recurring opinions regarding cleaning etc. Whoever has large windows likes it and whoever doesn’t, doesn’t, although with us people like it very much, usually without expressing any of the usual comments. Beautiful things are not always practical or come with consequences that you should know/be aware of. This time I was also a bit unsure because of heating up and because I don’t like overheated rooms, which is why we installed an air conditioning system so we wouldn’t be at the mercy of this problem. In retrospect it wouldn’t have been necessary for our building but it was still a great decision for us, also because with the photovoltaic system there are practically no operating costs and we also occasionally use it for targeted heating. Shading is very important, we have venetian blinds on the south/west side and I would strongly recommend that to you; we don’t have an overhanging roof. I would also recommend insulating the house thoroughly in general, so the roof, walls/facade; the energy consultant will also tell you where you should do more and where less; I would insulate as much as possible, for example with external roof insulation. Even in winter it often gets pleasantly warm in the house from 9 a.m. thanks to the sun, we like that very much. On the north side we have almost no windows, actually only where we need them as a source of light for the room, but that also depends on the location of the house. I wouldn’t insist on having windows everywhere because, as already mentioned, you need space for furniture as well. Post your plan here or pictures of it, then maybe more can be said, also information about the plot and orientation. The photovoltaic system brings you little in terms of heating in winter, but if the house is well insulated you don’t need much anyway. We have Kfw40 or better and I would recommend that to you, then nothing will happen.

The heating losses would not worry me as much as the heat gains in summer.

Yes. In a well-insulated house, it is difficult to get the heat out again – many forget that. Besides venetian blinds, there are options like rebates, roof overhangs, terrace sails, and awnings... Only the non-solution would be foolish.

Additional disadvantages of window fronts:

The "disadvantages" are all manageable. The space for furniture in large houses with large rooms is quite different from that in square-meter-optimized houses. Large window fronts hardly disturb there. The visibility into the house can be controlled by location and exterior design. Keep an eye when choosing the plot... Protection against burglars and storms – here glass naturally has fundamental but manageable disadvantages. And as for the appearance: Those who build a house in the seven-figure range should do well to select an appropriate architect. I know some phenomenally well-executed glass fronts. The increased price for a good solution remains a disadvantage in any case. But: If you can solve a problem with available money, then you should solve it with money. If you cannot solve a problem with money, you should not even try.

Aside from that, I see the question of heating costs in a house that will cost seven figures as unnecessary. Whether the heating costs increase by 25€ per month now is negligible.

"Watch after the pennies and the pounds will watch after themselves" Additionally: Some people do not want to discuss ecological issues at home – that a new single-family house is already an ecological catastrophe in itself comes up less often in couple discussions than the ecological footprint that is more immediately experienced through consumption behavior.

P.S. For such a special house with lots of glass, external professional heating planning is crucial. Then you have a well-functioning house in winter.

Absolutely yes!

Acquaintances now advise us to reduce many windows because allegedly there will be heat losses (winter) and we will have high heating costs.

Do your acquaintances advise you in the sense of "giving advice" or are they guessing in the sense of "actually, I have no idea, my half-knowledge tells me that..."? Gain certainty about your intent and then the possibilities of implementation. Then no one outside has to "advise" unsolicited anymore. Experience: We have large windows, you could also call it window fronts, a suitable roof overhang that keeps some sun outside in midsummer, and live quite well in the house. Not everyone’s thing – but certainly not wrong either.

Now the 2-meter deep balcony makes sense. Windows are great. I couldn't afford them. Or rather, I can't afford a very expensive house where window areas are part of the furnishings. However, in my personal opinion, a wall panel can positively support a large window area. Regarding insulation. Yes, some of it probably gets lost. But with 300 sqm, due to the additional, unnecessary area, quite a bit likely dissipates, so you can really call the windows a small issue. The window cleaner will be more expensive and will have to expend more energy.