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?

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

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

--
Charlie Pridham
Gardening in Cornwall
www.roselandhouse.co.uk

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)

--
Regards,
Martin Brown

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

On Wed, 8 Feb 2017 10:02:37 +0000, Martin Brown
wrote:

snip




Thanks to you and others for excellent suggestions

On 09/02/2017 19:26, Judith in England wrote:
On Wed, 8 Feb 2017 10:02:37 +0000, Martin Brown
wrote:

snip




Thanks to you and others for excellent suggestions


I've built propagating frames like that for many many years.
polystyrene underneath then polythene sheet over the base and up the
sides (sides being at least 4 inches deep) then about 1 1'2 inches of
sand, the cable snaked back and forth across the base with the wires
around 3 to 4 inches apart, then cover with another 2 inches of damp
sand. Cover with black polythene to stop the sand drying out and to stop
any roots getting into the sand.
A rod thermostat through the side of the frame so it sits just below the
surface and between the wires to get the best reading.
If you are going to use it for cuttings, if you can build a frame around
it covered with polythene sheeting, the front should have a curtain that
seals at the sides and goes down over the front. If you have a string
stretched tight across the front then you can tuck the sheet under it
and get a good seal, this will help to keep the humidity high and stop
wilting.
Good luck
David @ a dry but cold side of Swansea Bay

On 09/02/2017 22:23, David Hill wrote:
On 09/02/2017 19:26, Judith in England wrote:
On Wed, 8 Feb 2017 10:02:37 +0000, Martin Brown
wrote:

snip




Thanks to you and others for excellent suggestions


I've built propagating frames like that for many many years.
polystyrene underneath then polythene sheet over the base and up the
sides (sides being at least 4 inches deep) then about 1 1'2 inches of
sand, the cable snaked back and forth across the base with the wires
around 3 to 4 inches apart, then cover with another 2 inches of damp
sand. Cover with black polythene to stop the sand drying out and to stop
any roots getting into the sand.
A rod thermostat through the side of the frame so it sits just below the
surface and between the wires to get the best reading.
If you are going to use it for cuttings, if you can build a frame around
it covered with polythene sheeting, the front should have a curtain that
seals at the sides and goes down over the front. If you have a string
stretched tight across the front then you can tuck the sheet under it
and get a good seal, this will help to keep the humidity high and stop
wilting.
Good luck
David @ a dry but cold side of Swansea Bay
Snap!
With mine I built it so that a cold frame fitted on top. The cold frame
could then be covered in bubble wrap when needed. The only problem was
that the bubble wrap was not UV resistant but- with luck it waould lsast
2 years

Malcolm