On 08/02/2017 09:51, Chris Hogg wrote:
On Wed, 8 Feb 2017 09:04:46 +0000, Martin Brown
wrote:

On 06/02/2017 22:27, Charlie Pridham wrote:
On 06/02/2017 12:49, Judith in England wrote:
On Mon, 06 Feb 2017 11:36:10 +0000, Chris Hogg wrote:

On Mon, 06 Feb 2017 10:57:07 +0000, Judith in England
wrote:


I am putting in a new box in to my greenhouse which I will fill with
sand and put in a heating cable.

Some websites say bury the cable - others say leave on surface.

Views please?

On surface - or if buried - how deep?

I had one years ago, with the cable buried between 1 and 2 inches down
in the sand, and with the thermostat also in the sand but not in
contact with the cable. Burying the cable allows the temperature to
even out and equalise before it reaches the underside of whatever you
have in the box. Otherwise you get hot strips and cool strips, and the
thermostat measures the air temperature not the sand temperature.

Excellent - good points - cheers


As Chris says bury about 2" down with 2" below the cables and keep the
sand damp to allow the heat to spread

It is also worth lining the base with a polystyrene tile so that you
don't lose too much heat downwards.
(or equivalently standing the box on a polystyrene tile)

Good advice. As an alternative to polystyrene tile, consider lining
the box with bubble-wrap before adding the sand.

Until there is something growing a bubble wrap cover over the outside is
worthwhile too. Once some seedlings are up they need all the light they
can get at this time of year or they go weak and leggy.

A really cunning scheme I have seen cactophiles do is nested boxes with
the hottest small one placed in the middle of a larger one which then
traps the waste heat of the central hot box to provide a bit of extra
warmth for things that don't like 8C.

--
Regards,
Martin Brown