I put it in the little door that is usually the space above the toilet where the water heater is located, for those who understood, it is a little door that sometimes opens even a little bit from the air, by air I mean the pressure when you open another door... yes, it's an old house... maybe I didn't install it correctly, maybe it simply doesn't keep the door closed... whatever the case, it may be intended for another use, but unfortunately it didn't work for me.