This automatic vent opener contains a clever gel which expands and retracts according to temperature changes, adjusting the vent in your Vitavia greenhouse and ensuring that your plants are suitably ventilated at all times. Specifications Adjusts ventilation according to temperature Contains gel which expands and retracts with temperature changes Fits all Vitavia roof vents Dimensions: 10 x W24 x D36 Please be aware that we currently cannot arrange for delivery of this product to the following postcodes:AB, BB, BD, BH, BL, BT, CA, CF, CH, DD, DG, DH, DL, DT, EH, EX, FK, FY, G, GY, HR, HS, IM, IV, JE, KA, KW, KY, L, LA, LD, LL, ML, NE, NP, PA, PH, PL, PR, SA, SR, SY, TA, TQ, TD, TR, WA, WN, ZE