We have an oil filled heater that has a timer and a thermostat. So instead of leaving all the heating on I just leave this heater on in the room the hamster is. I found the thermostat is more effective than setting a timer. I leave it on 20 degrees. It seems to run a bit cold so doesn’t come on until it is below 20 degrees. But goes off again when the room
Is about 18 degrees.
So I leave that on all night (-8 here the other day!) and it prevents the room temp dropping too low. A cheaper way than leaving the hearing on on the whole house probably.
The heater itself was not cheap to buy though. We had a little one at first and that was fine in a small ish bedroom but in the lounge with high ceilings it had no effect at all. Even when in full all the time. So we got the bigger one. And now use that as our main radiator in that room and turn the ch radiator off in that room.
It’s not cheap but has a 10 year guarantee and the company replace them with a new one if it doesn’t last 10 years! (Hence I kept the box!).
It also has a safety cut out so I don’t worry about leaving it switched on at night.
De'Longhi TRDX40820E Oil Filled Radiator, Multicolour: Amazon.co.uk: Kitchen & Home
During the day it would save you leaving the central heating on as well. It’ll soon be spring! But right now it can get sub zero at night. In autumn I had the thermostat set to 16 degrees and it rarely came on as it rarely got below that indoors. So it’s just in case it gets really cold.
You can also get snuggle safe microwave pet water bottles to put under the cage. But again I didn’t find that very effect in a draughty fair sized room. I had mine attached to the side of the cage using a clip on towel holder and the snugglesafd just sat in that about a couple of inches away from the bars.
If the room temperature is freezing that won’t be enough really. Some people have used a heat lamp which might be cheaper to run - not too close to the cage. But ideally just keep the room at a reasonable temperature.