The most common and most likely answer to this crossword clue is the 9 letter word OIL-FIRED
I've seen this crossword clue in The Guardian
O
I
L
-
F
I
R
E
D
Buddy explains!

The straight part
We know that "Type of heating" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case type of heating = oil-fired.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OIL-FIRED mean?
OIL-FIRED adjective- In boilers and heating systems, burning oil as a fuel to provide heat.