If the ambient temperature of your reptile room gets to 30 degrees plus, theres no need for any cage heat.
When you know the room will reach these temps just shut it all off, even the night before. In summer if the room gets to these temps 30+ it'll hold that heat for long enough hours for the snake to acheive whatever body temp it needs, just like it would on a basking site. All snakes need a temperature of around 24-28 degrees to kick in the immunity system and produce enzymes etc for digestion and bodily function, so in summer when night time enclosure lows are around the 24mark and day time highs approach 30+ they really don't need any mechanical extra heat at all.
I do very few call outs on to snakes on the 35+ degree days, its too hot for them, and they can acheive their temps very easily, by staying hidden away, however the lace monitors love these high temp days and are mobile.