When Katy Perry sings “’cause you’re hot, then you’re cold,” she’s really just saying you need to get yourself a Dyson Hot+Cool. At least, that’s how I like to think of it! Because this device really is quite cool. Right now, you can get this Dyson Hot+Cool for just $315 on Amazon, which is a $155 discount (33% off) on its original $470 MSRP. The Dyson Hot+Cool AM09 is a combination heater and fan that heats up your room during the colder months and cools it down during the hotter months via convection and air circulation. It also oscillates at a 70-degree angle for more efficient room heating…