De or het terrasverwarming?

The correct Dutch article is:

de terrasverwarming

Rule Words ending in -ing: almost always de. See the rule

How to use terrasverwarming

the terrasverwarmingde terrasverwarming
this terrasverwarmingdeze terrasverwarming
that terrasverwarmingdie terrasverwarming
our terrasverwarmingonze terrasverwarming
your terrasverwarmingjouw terrasverwarming
every terrasverwarmingelke terrasverwarming
which terrasverwarming?welke terrasverwarming?
a big terrasverwarming / the big terrasverwarmingeen grote terrasverwarming, de grote terrasverwarming