Not too big a deal. You can achieve it using many methods. As pointed out by Alekh you can use temperature sensor, relay and arduino. you can use expeyes interface with temperature sensor and relay. you can use simple hardwiring circuits logic gates and sensors to achieve the same. depends what you want to go for. software enabled system (which is more versatile) or hardwired system (quicker but less versatile). You can do the same with your android mobile too. and trust me it works beautifully if you know how to interface it.