Not a new concept I have been keeping snake at room temp only (85/88 degrees daytime) 7/8 months out of the year for 7 years since the room naturally gets hot (being under the roof and being cut off from the AC system intentionally helps with that). I run my main snake room at no cost most of the year. Of course it does mean there is a fluctuation of about 5 degrees from day to night which is really perfect.
I prefer to incubate in an incubator however, and that incubator is in the second snake room, (colubrid room) which is much cooler.
As for you rats if you want to produce less 88 will definitely do it, optimal temps for rat production is 70/75. Above 80 production will start to drop and rats start to overheat over 88.
Now you can maintain a room at a stable 88 degrees with a heater I know a few breeders that do and some that have done it for decades, now it is cost effective? Well it depends on the size of the room and what it takes to heat it up to 88 vs the number of racks and what it takes to keep a hot spot. It's all about wattage usage. For some it make sense for other it would not.
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