You don’t typically think of candles as effective heat sources, at least not to heat up an entire room. However, the Egloo terracotta heater claims to do just that. By using four small candles and two nested clay domes, it is able to generate enough heat to warm up an office sized room for up to 5 hours at a time. After that, just get a new set of candles. These are super cheap, going for as little as $4 for 100 at IKEA.