hi zemcimil
if your in the uk mate as i am , and by the sounds of it your in a old victorian house then cant you exhaust up a chimney, i do, any body flying over looking for heat are only gonna see heat coming out of a chimney, just where its supposed to come from lol, i also find that air extraction is a piece of cake this way and very very effieciant, as for burning 4000 watts, yes it is a lot, be safe mate burn your lights when the household is most active, if your burning all your power when most people are sleeping then that may atract unwanted attension, yes its still iligal here in the uk, i think you would be hard prest to convince a jury that around 250 plants are for personal use eh !!!, be carefull mate and peace to you