A firefighter was injured trying to put out a blaze in St Albans on Friday night.
Police confirmed the the single story brick veneer house on Kings Road contained hydroponic equipment which was being used to grow cannabis.
A spokeswoman for the Metropolitan Fire Brigade said it got several call about the fire at about 8.30pm and seven trucks went to the scene.
It took the firefighters just 20 minutes to get to the fire under control and it was contained in the back portion of the unoccupied house.
One firefighter was injured by a minor explosion inside the building, but he was assessed as fit for duty soon afterwards.
Police are investigating.