Install insulation or order coal for 40 years?

We've already calculated this x times... Even insulation steps from T9 to T8 pay off after about ~20-30 years.
Quite simply: an uninsulated old building has a heating energy demand of 450 kWh per m² - which amounts to 45,000 kWh/a energy demand per year for 100 m². That would cost €2604 per year in gas.
If you insulate fully for 20 T€ (I find that rather cheap), the house would still have 50 kWh per m² heating energy demand - so 5000 kWh/a. That would cost €394 per year in gas.
Even with compound interest at 3%, you have a payback time of 10.37 years.
The depreciation period for a house is 70 years.
qed.

... even if the insulation costs 40,000 T€, it still pays off.

If you absolutely want to heat with coal, each to their own. And in summer, do you then take the briquettes and stack them as thermal insulation in front of the outer walls or what? (Black Castle) ;) don't forget, a year doesn't only consist of winter when heating is needed. In summer, the insulation works exactly the opposite way and the heat stays nicely outside. Then you must not forget in your great economical calculation, if you heat only with coal you need a lot of coal which also has to be stored. Costs: coal shed xxxx€, larger property because more space is needed for the shed xxxx€ :rolleyes: , coal turns into ash and ash means waste and waste means costs again. I could go on like this for hours. And of course the work the musketeer already mentioned.

How much coal can you order now for the money that insulation alone consumes? -- Based on experience, for a single-family house, depending on the construction method, 500-1000 EUR per year is needed.

Well insulated, that's about right, yes.

-- That makes 20 to 40 years during which you could heat with coal, for the same money the craftsman carries out of the house within a few weeks for the great insulation.

45,000 kWh/a x 0.055 EUR/kWh = 2,475 EUR + delivery + storage costs

Bet you the insulation will have fallen off the wall again by then? Maybe the house isn’t even standing anymore because it was demolished 10 years after the insulation measure due to mold formation.

If the insulation pays off after an estimated not even 5 years compared to coal heating + storage costs + transport costs + imputed hourly wage for heating, then the insulation outside still looks like new. You could have mold formation with the uninsulated house, yes. With the insulated house, the temperature on the inside of the exterior walls is significantly higher, so condensation and thus mold are much less likely.

What do you think about that?

Why not just move into a used, old motorhome and drive south in the winter? That really saves money! And if you want to air out: roll down the window and hit the highway. That creates a brilliant air exchange rate.