nah its ok in there, im in north west UK. i was in there last night and it was abit warmer than outside, only a tiny abit.
i put the veg lights on and just stood in there for a minute or two. it was fairly warm but thats a good thing atm.
whilst there only 2 days old the warmth will help them sprout abit...
once the heat starts to become an issue, a fan will easy sort out the heat problem.
plus at night the temp drops as well.
it seems fine for now. im quite suprised i did so well to make a semi - 'pack up grow room'
my gf knows about the cable running through the cat flap and she is ok with it. i told her i was growing tomatoes and not to let any1 in the kitchen or back yard - and they cant get in the shed anyway coz its locked.
so if i am expecting guests ill tell them come round about *time* when my lights are due to go off..... unreal the extension cord, chuck it in shed. lock shed. boom. job done
im really happy with it. ill post pics probs 2morro.