Spring inside

Not sure which species of butterfly this is but it was keeping warm in the old sink in my utility room last night. I can't decide if it is kinder to let him stay until the snow goes or if the indoors will harm him more.
There again I just need to make sure I don't forget it is there and turn the tap on when I go to give the house it's weekly deep clean. Aye right! No chance that will happen soon!