When Council / housing associations / MOD ( ive worked for all 3 ) houses lost heating, we always used to supply these
https://www.screwfix.com/p/ch-2000m-...st-2000w/716fy
ive got 2 in the shed for emergencies, they work well and while 2000 W will not be as cheap as 1000 W, they do work well
I fitted one of these
https://www.screwfix.com/p/blyss-sar...te-1500w/195jk
in the mancave / games room, I went with 1500 W as its slightly cheaper to run, I can run all the power ( with this heater included ) from a 13A fixed spur unit ( or a plug if needed ) as its all under 3 KW of power
it heats a 5 M X 3M well insulated space really , last week it was Minus 4 C outside and I was sat in there with a hoodie and some joggers on, when I started boxing ( in VR ) I had to take the Hoodie off, so the heater was well upto the job and cost 40p per hour to run
this site has a calculator with all the tariffs
https://www.sust-it.net/heating-energy-calculator.php
select the size of your heater and away you go