I thawed the pipes, wrapped them in newspaper, noticed a joint was leaking slightly (Old, rusty pipes - they ned to be replaced ASAP) and set up the halogen light so it was shining on them and (hopefully) creating a little pocket of warmth in the cold. It was - 14C, which works out to be about 8°F.
The next morning the pipes froze again, and this time my husband volonteered to man the hair dryer. I re-wrapped the pipes (the newspaper had fallen off) and then wrapped them again with a polo wrap for horses, lol. Bright red. Very festive. Light is still on in the shed, so our electricity bill will be be horrid for this month.
But it's lovely to walk in the snow, play in the snow, slide in the snow, and throw snowballs at everyone.