Advise please on building a heated greenhouse bench

[ladybird]

As I now have electric in the Greenhouse I have been contemplating making a heated bench. I know a few of you have done that and I would greatly appreciate your advise .My strong table is 127cm long X 73cm .I was wondering how much cable it would need ? I see 24 meters for £39.99 on eBay and £23.99 for a thermostat is that a good price ? and do you think I need that much cable ?

I would mainly use it for trays of seedlings and perhaps a few cutting later on . (I presently use 4 electric windowsill indoors ) As I have loads and loads of seeds and usually have endless seedlings to keep warm for a few weeks I might be tempted to make two, one on the opposite table and perhaps have two layers ( swapping the seedlings about for light )

Also there is the covering what could i use for quick access ? I had been using a polycarbonate cold frame sitting on the bench with a paraffin heater and two layers of wire mesh it was difficult to access the bottom trays and the panels are beyond repair now having been outside in the wind .

[caretaker]

I can only tell you what I made last year but I will only use old imperial measures.
The bench top is 4 feet long by 2 feet, my heated cable is 20 feet or 6 meters.
I got some wood for the sides and front 3 inches high and screwed this to a ply board base 4x2, I did have an old bit in my shed it was about 1/2 inch thick.
Lined this with plastic sheeting or like me I had some lino.
I brought 2 bags of course sand and filled this in to the unit then laid the cable and connected the thermostat, got one bag of fine sand this was sand that they use for laying brick drives, put this on top.
Then made a frame on top with a hinged roof and front, covered with plastic sheeting.
Advise, do make sure that your bench will NOT sink with the weight from the sand, I am going to change some of the sand for Perlite but have not tested this yet.
Best of luck if you take up this project, I got my cable from ebay new, I have only turned it on to day for the first time so fingers crossed.

[ladybird]

Thanks caretaker. A hinged roof and front sounds ideal . My table legs are 2X2 and on heavy clay and stones, I doubt if it would sink .what size of cable did you buy ? I could swap my tables around and put the longer one near the sockets it`s the full size of a door 6 foot 8inches X 32 inches. I recon a 24 meter cable (78foot ) would wind up and down the table 10 or 11 times, that's 3 inches apart would that work ok do you think ? I`m afraid of it being too hot then again no point in it not being hot enough Oh I`m so excited about this project.

[caretaker]

More suggestion, I think the length you say would do, try with a piece of string, 3 inches between is fine but if you can get the thermostat that go's with it, you have to drill a hole in the front well two holes, one for the stat and one for the cable, plus you have to connect it up but that is strait forward.
I just set the thermostat to 10deg c and that's it.
I checked it this morning after it has been running all night and it kept the temp at 10 centigrade.
As long as you table/bench will take the sand, as I had to re-do mine as it sunk, I am waiting for some Perlite to come and will reduce the sand with this.
Good luck Reg

[ladybird]

Thanks again caretaker. I might not be able to move the benches as I have the electric plugs screwed to one , I had forgotten . Wonder if a 12 foot cable like yours would do, my smaller tables are roughly the size of yours. What are you intending to do with the perlite ? I just read an article that says you can`t use perlite or compost directly with soil warming cables because of their insulating properties .

[caretaker]

[ladybird]

Oh wow ! that brilliant caretaker Thanks for posting the pic it`s perfect see you have the perlite on top of the sand , good idea . do you think your cable gives enough heat ? i don`t want to overheat mine .

[caretaker]

The Perlite is an experiment as I am trying to reduce the sand.
The cable gives plenty of heat so far as I have it now set below 10c but will have to keep an eye on this.
I think the cable was 20 feet, I do know it cost £29, you do not get heat at the ends, about a couple of feet.
I am tempted to empty all the sand out and were you lay the cable at the ends put some nails in that will stick up about an inch and tie the cable to them to make a neater job on the bends, when you lay your cable you will find it to have a mind of its own.
My other job will be to change the plastic top with glass but will not be doing this till summer time, mainly lack of money as I have a wedding coming up.
Any one good at writing speeches?

[ladybird]

I might use polycarbonate on mine as it is much lighter and the inside of the polycarb has a coating that prevents drips. I may also make my lid slightly sloped for the condensation to run off better . I`m really impressed with your work

[ladybird]

I`ve just read an idea about using an electric blanket in a propagater. i could buy a used on on eBay for less that a £5 . would it be possible to remove the cable from the blanket and use as a heated cable . the item i`m looking at says the blanket is washable .Anybody any thoughts on that .

[daitheplant]

Feb 10, 2014 19:01:31 GMT ladybird said:

I`ve just read an idea about using an electric blanket in a propagater. i could buy a used on on eBay for less that a £5 . would it be possible to remove the cable from the blanket and use as a heated cable . the item i`m looking at says the blanket is washable .Anybody any thoughts on that .

I wouldn`t risk it ladybird, it may say it`s washable, but not when it`s switched on.

[ladybird]

yes I know your right .

[daitheplant]

If you intend in droducing a great number of plants it would be well worth investing in the cable and thermostat and doing the job properly, if you are only producing a few plants, then invest in an electronic propagator.

[ladybird]

I`ll have many hundreds of plants daitheplant and every year the number grows and it gets more difficult to keep the seedlings warm in the greenhouse through the cold snaps . I`m trying at the moment to figure out the length of cable I would need for a 6` table and roughly how much it will cost to run over any 24 hour period. the 24 meter cable is 300 watts does that mean the entire heat supplied by the cable is 300 watts or is it the wattage over per square foot or square meter meter I am reading conflicting info about that.
300 watts a day I think would roughtly cost £2.10 a week and I can`tbelieve that it costs so little .

[daitheplant]

What width of table are we talking about?