If you have a garden building with heating can you give me some advice please

[CovidCorvid]

I'm having a 3m x2.5m wooden garden office built. Insulated roof and floor, non insulated walls but thicker wood than a shed.

I need to urgently make a decision about what kW of heater I need and haven't a clue if I need 2000w or 1500w.

The sparky is giving me 2 quotes for electrics. The cheaper one will run a spur from a socket at the back of the house but limit me to 13 amps which is about 2700 Watts. As well as the heater I need lights, laptop charger and TV. So personally I think even with a 2000w heater it's OK.

Sparky is not sure and advising I go off the main electric box which will involve taking floorboards up, bigger quote.

I'm just nervous incase even 2000w heater isn't enough in winter and I need a 3000w one.

If you can afford it even at a push I would go off the main box. What if you want a kettle or we have a bad winter etc. I can imagine nothing worse than being cold or juggling your electrics.

The quote for the cheaper option is 1k so dread to think how much the more expensive option will be. 🙈