Your heat lamp is way too hot. That will kill the chicks. I strongly suggest that you return it if you can, or toss it in the trash if you can't. You can easily build a MHP cave with a heating pad and a piece of fencing or a cake cooling rack. @Blooie has a thread and 2 articles about this method. Those of us who have tried the MHP system will never use a heat lamp again. And yes, the MHP can be used in an outdoor coop with temps down into the 20s. This system is much safer for the chicks, very closely resembles the heat provided by a broody hen, and poses much less risk of fire when compared to a heat lamp.