You can grow good plants in a pantry like that, but you need ventilation. If you are using a HPS SOdium light, how many watts? A small 400W will not put off enough heet unvented to hurt any plants as long as you have a supply of fresh air to the room and an exhaust. This is important. The plants need fresh air to absorbe CO2. And you need exhaust to expell the moisture from the plants transpiring, and the co2 depleted air. Hope I can help. If necesarry cut a hole in the ceiling to the attic if applicable or use air from another room.