New greenhouse, advise for heating and hotbed.

[steve76]

Hi all,
putting down the base this weekend and next weekend getting a new 6 foot by 10 foot  greenhouse massive upgrade from my 4 foot by 6 foot 
any how in this one i would like a hot bed for germination so the wife can have the dinning room back and also advise on heating for the colder nights, ideas for staging aswell. ( electric feed already in hand )
  sad but so excited  

Thanks steve.

[steve76]

[Tee Gee]

This is my set up so you might get some ideas from it:

http://www.thegardenersalmanac.co.uk/Data/Greenhouse%20heating/Greenhouse%20Heating.htm

[steve76]

Thankyou, just the advise i was looking for and pictures are brilliant..

[sunloving]

Hi Steve happy new greenhouse!
I made cheap and easy staging from fencing posts and old doors, since you are quite narrow maybe those shower cubicle or louvre doors or just planks would suit.
I made a 40 ft stretch of benches for leass than£50.
Good luck with your new place"x sunloving
Hhh

[Tee Gee]

pictures are brilliant

In case you have not noticed! Clicking on them will enlarge them a bit!

just the advice I was looking for

Glad to have been of service...Tg

[steve76]

Hi all and happy new year to you,
So i finally got round to making the hotbed but im a little worried ive done some thing wrong as you can hardly feel any heat on the sand ???
Ive got 2 cables at 3 meters each rated at 50 watts.
i was expecting temperatures similar to my little electric propagator...
any help!!
Thanks Steve.

[Tee Gee]

A bit more detail would help!

My first impression is 50 watts seems to me to be a bit low.

You do not mention the size of your bed or the spacings between the lines of cable.

So can we have a bit more detail.

Do you have a thermometer you can lay on top of the bed to see what the actual temperature you are getting.

I look forward to your reply..........and a Happy New Year to you too

[steve76]

Hi its only a small bed 500 wide by 1200 long, the cables are approximately 3" apart and i've just been out and i had put a digital thermometer on some compost in a seed tray on top of this bench so to simulate seed germination and that is reading 9.4 celsius. cold to touch as does the sand.
i was thinking the watts was to low but i've only seen higher watts on longer cables, i've got 2 x 3 meter.

just to add i have 2" polystyrene sheet at the bottom 2" sand then cable then 2" of sand is this correct?
thanks.

[ancellsfarmer]

Dont panic!
It will take sometime to raise the temperature of that volume of sand. Once up to temperature, it will hold pretty steady. 50 watts is probably sufficient. A cover of polystyrene would help.Individual "tiles" size as seed tray. Personally have cut strips in 50mm material to go around the edges as well. Remember to lift the lids daily and remove once signs of shoots. Have you got a thermostat control?

[Tee Gee]

I am no expert in electrics but 50 watts is very low and no matter what you do you will not get any more heat from it.

With 2" of cover this seems rather deep my cable is barely 1" deep.

As I see it you have a lot of sand to heat first before any heat gets to where you want it.

I would suggest you raise the cable to something like 0.5"to 1" deep and see what result you get.

I would try dry sand first and then check the temperature, once you have done that, then wet the sand and check it again.

I have had people say that it does not make any difference whether the sand is dry or wet as the heat source will still produce the same heat choose which way you use it.

My own preference is wet, as I get the impression the moisture (water) warms up and radiates the heat better plus it creates a nice humidity so my seedlings are kept just nicely moist, meaning I do not have to water them much thus reducing the risk of damping off.

I have no scientific proof of what is happening but it seems to work for me!

All I can suggest is you try sinking it to various depths.

You mentioned the heat in your propagator being hotter,what you must remember is that there is probably less than 1 mm thick of plastic covering the heating element.

So with this in mind shallower cover can only improve you situation.

Sorry I can't suggest anything better !

[steve76]

Thanks for the help all,
I've had the hot bed running for a few days now with 2" of top sand ( was going on what i could find on the internet ref sand cover ) and it's got no hotter, i have tonight taken 1" of sand off and so far not a lot of change ??.
I'm in the thinking that i need to find higher watts cable for the short length that i need??.
nearly forgot i have a thermostat but not got it wired in yet as wanted to test it all.

again thank you for your help.

[PondDragon]

I made a similar sized hotbed using a 12 m 150 W cable with a thermostat. So with two 50 W cables (100 W total if I understand you correctly) you should be getting a reasonable amount of heat through. Have you moistened the sand with enough water? It needs to be damp to conduct the heat properly.

[steve76]

progress report, i've taken another 1/2" of sand of the cables, wet the sand a little more and i am now getting soil temp in my trays of 20 celsius.
Think i'm finally getting their..
Thank you for all your help..

[Tee Gee]

Think i'm finally getting their..

Pleased to hear it!