Unit at health centre finally has room (5)
I believe the answer is:
therm
'unit' is the definition.
(therm is a kind of unit)
'at health centre finally has room' is the wordplay.
'finally' says to take the final letters.
'has' says to put letters next to each other.
'room' becomes 'rm' (I've seen this in other clues).
The last letters of 'at health centre' are 'the'.
'the'+'rm'='THERM'
(Other definitions for therm that I've seen before include "Unit of heat used in the UK as the basis of gas bills" , "A hot unit" , "Unit of measurement of heat" , "Indicator of heat" , "Gasman's unit" .)