How low can you go?

OK, last minute question as I am about to go on vacation to Florida where it is warmer than here in the (last British stronghold) North-East.

What should I set the heating at while I am away to stop the pipes freezing? Lows are in the 20s this week.

House is a rambler with thermostat on the main floor. Water pipes are in the basement below.

It depends somewhat on where the pipes go. If there are any in an outside wall, you may not want to drop the temp much at all. If there are any sinks on an outside wall and the supplies run in the wall, you may want to leave the cabinet doors open. One thing to consider is that while you may get the air temp up fairly quickly when you return, it will take awhile for all of the walls, furniture, floors, bed, etc. to warm up. It might be an uncomfortable day or so. If none of this bothers you, drop it to say 50. Furniture, some medicines, etc., don't like the cold either. Some refrigerators have trouble in the cold, but that's not too common although it might have troubles doing an automatic defrost.