Heating suggestions for house with no central heating

[TheDarkLordOfMuffins]

for those of you that need to provide heat for your tarantulas what do you use? I have been told to heat enclosures individually, use a space heater, or put a heatmat on the wall behind the enclosures to heat up the ambient temp around them. I am looking at the most cost effective option as we have storage heaters and no central heating *yay council* I have Asian Forest scorpions as well so i am mainly concerned for their heat needs as i know t's adapt fairly well. the room is usually 21 at night lowest 20 with daytime temp being 22 highest 23 *at least with current weather. I live in the UK so anyone with experience with council houses like mine would be greatly appreciated.

 

[The Snark]

21 at night lowest 20 with daytime temp being 22 highest 23

Normal temps for Asian scorps in the wild, mid October through March. Right now is romance time then they dig deep into the detritus to weather out the hot season. Most efficient heater involves thermal battery.