How about a timer and some heat trace wire(made bt Ratheyon)
----- Original Message -----
From: Dave Bell <dbell@THEBELLS.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, January 10, 2000 11:05 PM
Subject: Subject: Keeping pipes from freezing


> Nicholas Irias <nirias@PACBELL.NET> wrote:
>
> >I'm wondering if anyone has ideas on making a custom furnace controller
> >to keep pipes from freezing in an unoccupied house, while minimizing the
> >amount of energy consumed.  Standard thermostats just try to keep the
> >interior at a constant temperature, which wastes energy most of the time.
>
> >The furnace can even be off so long as the outside temperature is above
> >freezing.  But when the outside temperature is above freezing, you need
> >to maintain somewhere around 55 degrees F inside the house to ensure that
> >pipes inside exterior walls are still above freezing, since there is a
> >thermal gradient inside the wall.  If you get a terrible cold snap, you
> >might even want to raise interior temperatures above 55 degrees.
>
> Well, throw me off the PICList, if you must, but for simplicity and
> reliability, I'd bury a mechanical (bi-metallic) thermostat within and
> outside wall, possibly even thermally bonded to a cold water pipe. Set it
> for ~35F, and wire the contacts in parallel with the furnace
> thermostat. If your location is subject to freezing winds that might come
> from any direction, put one in outside walls facing four directions.
>
> Dave
>