The 70/30 rule in heating cost billing — simply explained with an example

Almost every heating cost statement contains a figure such as “70/30” or “50/50” somewhere. It determines how strongly your own heating behaviour affects your costs. Once you understand the rule, you can check the calculation in your statement — and judge whether the key suits the building.

What 70/30 means

The heating costs of a building are divided into two pots. The smaller pot, the basic costs, covers the part that arises regardless of the residents’ behaviour — for example heat losses through walls, roof and pipes, which partly heat every flat. It is allocated by living space. The larger pot, the consumption costs, follows what was measured at the radiators of each individual flat.

How the calculation works

Our example building has six flats with a total living space of 480 m². In the billing year, heating costs of €9,600 were incurred; the heat cost allocators in all flats recorded a total of 12,000 units. The costs are allocated on a 70/30 basis.

So Flat A pays €980.00 for heating. The units of the heat cost allocators are not kilowatt hours but relative values: what matters is what percentage of all units recorded in the building is attributable to one flat — here just over eight per cent.

70/30 or 50/50 — what makes the difference?

The allocation key does not change the costs of the building. It only shifts who bears how much of them. If we calculate the same building on a 50/50 basis, the consumption price falls to €0.40 per unit and the floor-space price rises to €10.00 per m². For the economical Flat A, this results in €1,100.00 instead of €980.00.

The rule of thumb is therefore: the higher the consumption share, the more it pays to heat economically — and the more households that heat a lot pay for their extra consumption. That is exactly the intention of the HeizkostenV.

Is 70/30 mandatory?

70/30 is often described as the legal standard. That is not quite correct. The ordinance allows any share between 50 and 70 per cent. 70 per cent is mandatory only in one narrowly defined case.

The idea behind the rule is simple: in such buildings, the insulated pipes lose little heat along the way, while the heating demand is high — so the residents’ behaviour has a major influence on the costs.

Conversely, there are buildings with predominantly uninsulated pipes, in which a considerable part of the heat is given off through the pipes and cannot be recorded by the heat cost allocators. For this case, the ordinance allows consumption to be determined in accordance with the generally accepted rules of technology and the pipe heat to be taken into account separately (§ 7 Abs. 1 Satz 3 HeizkostenV).

Which key is the right one?

Outside the mandatory cases, the building owner has a choice. A sensible key is one that matches the actual heat distribution in the building.

Who decides — and when may it be changed?

The key is set by the building owner. In an owners’ association (Wohnungseigentümergemeinschaft), the owners’ meeting decides by resolution. Once the key has been set, it can only be changed under certain conditions.

For landlords, this means: if you want to switch to 70/30 after an energy-efficiency renovation, you should announce the change before the start of the new billing year. A retroactive change is not permitted.

And what about hot water?

The same range of 50 to 70 per cent by consumption applies to hot water costs. The key for hot water does not have to match the key for heating — in practice, hot water is often allocated 70 per cent by consumption, because consumption depends almost entirely on the residents’ behaviour.

You can read more about the structure of the whole statement, allocable costs and deadlines in our guide to heating cost billing.

This article is intended as general guidance and does not replace legal advice in individual cases. Last updated: September 2026.