This YouTube user claims that using just four tealight candles in a bread loaf tin covered with ceramic flower pots can warm up a small cold room relatively quickly. People who’ve used this small life hack explain that this is much like how radiators work, via convective heat transfer. Of course, this won’t heat up a living room or anything larger than a small bedroom (or office)! If you have cats (or any animals for that matter), make sure to keep them away from this because they can knock it over (and they might start a fire). Happy heating!