Also, even with the cover, you might end up with convection
currents within the box, due to the concrete staying warm while
the air above cools at night.  Some people put a small (10 watt?)
heater or light bulb inside the top of the box, causing the air at
in the box to stratify.  The idea is to make sure each layer=20
of air is warmer than the one below it to eliminate convection
currents.

Jack

-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@...............
On Behalf Of Benji Johnson
Sent: Wednesday, October 18, 2006 3:57 PM
To: PSN-L@..............
Subject: Re: Questions

Hi Ted,

I don't know how much practical difference this makes, but in addition
to placing an insulated cover over the sensor, I also place 1/4" of the
rigid foam insulation on the concrete floor, in order to further
insulate it from temperature changes.  This extends 6 - 8" beyond the
outer edge of the box.  If you place your sensor onto this foam, the
feet will leave an imprint, which you then need to cut out slightly
oversized with a knife so that there is contact with the floor.  If the
legs on your sensor are longer, you could go with thicker insulation,
but you don't want there to be any contact with this insulation.=20
Lastlly, I attach a soft "garage door" insulation strip onto the floor
insulation, which the box then sits upon.  This seems to provide a nice
seal against air leaks between the two hard insulation surfaces.

In the past, others have mentioned filling some of the empty space
within the cover with light foam, so as to displace air which might
otherwise cause problems if it becomes convective.  On the other hand, I
could see this being a problem if all that you end up doing is focusing
the remaining air movement onto the coil.

Again, I'm not sure that either of these additional steps make a real
difference, but thought I'd throw them out as food for thought.

Benji
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