das Heizöl
heating oil
A liquid fuel obtained from petroleum and used to operate oil heating systems in buildings.
Wir müssen bald neues Heizöl bestellen, der Tank ist fast leer.
We need to order new heating oil soon; the tank is almost empty.

heating oil
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heating oil
A liquid fuel obtained from petroleum and used to operate oil heating systems in buildings.
Wir müssen bald neues Heizöl bestellen, der Tank ist fast leer.
We need to order new heating oil soon; the tank is almost empty.

The word is clearly made up of 'heizen' (to heat) and 'das Öl' (oil). So it describes exactly its function: oil that is used to heat buildings.
Die Preise für Heizöl sind in letzter Zeit stark gestiegen.
The prices for heating oil have risen sharply recently.
Since heating oil is a fuel that needs to be refilled regularly, typical verbs are 'bestellen' (to order), 'liefern lassen' (to have delivered), and 'verbrauchen' (to consume/use up).
Wir sollten bald neues Heizöl bestellen, bevor der Winter kommt.
We should order new heating oil soon before winter comes.
'Heizöl' (heating oil) is often the first part of longer nouns that relate to this topic. Examples are 'der Heizöltank' (heating oil tank), 'der Heizölpreis' (heating oil price), or 'die Heizöllieferung' (heating oil delivery).
Der Techniker muss den Heizöltank im Keller warten.
The technician has to service the heating oil tank in the basement.
oil
'das Öl' and 'das Heizöl' can easily be confused because heating oil is a kind of oil. But 'Öl' is much more general: it can mean cooking oil, machine oil, or also crude oil. 'Heizöl' is only the liquid fuel used for an oil heating system. When talking about cooking, you say 'Öl'. When it is about the tank in a house or heating, 'Heizöl' is more precise and more natural.

Vor dem Winter bestellen wir neues Heizöl für die Heizung.
Before winter, we order new heating oil for the heating system.
Für den Salat nimmt Maria etwas Öl und Zitronensaft.
For the salad, Maria uses a little oil and lemon juice.