So how much energy does one need to heat a house to let's say 20°C when the outside temperature is let's say -10°C? The scientific answer to that is "it depends"; and what it depends upon is mostly insulation. Just imagine under these conditions you would leave your windows wide open, it is obvious that it would be nearly impossible to heat a house like that. Basically the energy in form of heat that you need to provide to a house to keep it at a certain temperature is equal to the heat energy leaving the house. And that depends on how permeable the surfaces of the house like walls and windows are to heat, and the temperature difference between inside and outside.

The good news is that while perfect insulation is impossible (it would suffocate you), it is totally possible to insulate a house to a very high degree, so that even if there is a big temperature difference to the outside, very little heat needs to be added to the house to keep it warm. If you ever hear terms like "zero energy building", that mostly is about that sort of insulation. That is somewhat easier in Europe, where even basic houses are mostly built out of bricks, than in the US, where many houses are built out of wood. But zero energy buildings do exist even in the US. And in more climate change conscious Europe, building standards are evolving to require better and better insulation.

A well insulated house means that even if energy costs are high, heating is still affordable. And even in cases of extreme events, like winter weather resulting in long periods of electricity outages, you could keep a well insulated house warm with just a propane heater. As most people heat with some form of fossil fuel, widespread improved insulation would also significantly reduce carbon dioxide emissions from heating. And insulation works both ways: If the outside temperature is cold in winter, but hot in summer, it is also easier to keep an insulated house cool with less energy. As a personal note from living in a zero energy building, insulation is also not limited to heat, and also works well against noise from the neighbors.

So why aren't we all living in well insulated houses? Because insulation is expensive. A lot of young people are complaining about how housing was a lot more affordable for previous generations. That is supported by graphs showing an increase in the average cost of a median house divided by the median income. But if you look at the data closer, you will realize that "a house" bought in 2026 is both larger, and built to higher building standards, including insulation, than a house built in 1976, which explains at least part of the higher cost. In most places, building a house to 1976 standards today would be simply illegal.

The biggest problem with insulation is the large existing housing stock. Well insulated houses obviously have much thicker walls than less insulated houses. But if you plan on insulation while constructing the walls, that is easily manageable. Adding insulation to an existing wall is a lot harder, and needs thicker coats of insulation materials added. You don't want to add those on the inside, as it would very much shrink the rooms, but adding them on the outside isn't that easy either. You can improve things for existing houses, but it would be very hard to get to the same degree of insulation as a newly built zero energy house.

So the world is moving towards better housing insulation, but slowly. It is something to think about if ever you are in the situation where you would construct your own house. Insulation makes the house more expensive, but the payout for reduced energy cost of heating and cooling in most places makes this an investment with a very good yield.