Topic: Advice of buying electric greenhouse heater.

[George the Pigman]

Now I finally have electricity piped to my greenhouse I am looking for the best way to provide heating. Its a 10ftx6ft greenhouse and I am really only looking to heat it in early March onwards to get those seeds germinated early and grow the plants on.
Any ideas about the best way of approaching it and any suggestions about what to buy would be gratefully received.

[Tee Gee]

This is my set up !

It might give you a few ideas;

http://www.thegardenersalmanac.co.uk/Content/G/Greenhouse%20heating/GH%20Heating.htm

[ed dibbles]

I use tubular heaters to keep the frost out of my bubble wrapped greenhouse in winter while using a propagator indoors to raise seedls initially before transfering them to heat mats in the greenhouse. 

[ancellsfarmer]

Its the cost of electricity that causes concern (about 14p per kwh)Try to warm surfaces not air that then rushes upwards to escape.Some insulation (bubblewrap) helps. I have (apart from the 'germinator' elsewhere described) a heated bench built cheaply in scrap 4x2 along 1 side.Contains a 15w (?)soil cable in a 2" bed of sharp sand upon a bubblewrapped plywood shelf. This provides bottom heat (hopefully 40 deg F )for growing on.Topped with polythene under a further 6mm of sand to reduce evaporation/saturation to restrict weight.Above the tray I have built a second 'greenhouse' in 10mm polycarbonate, with a lifting hinged lid coupled with a wire coat hangar to the auto roof vent in case of hot weather in April.I also have a B&Q 2Kw GH fan heater with a thermostat as a emergency, but not very sensitive, for sudden frosty nights.Aim to maintain a minimum/maximum of 40deg F. If you are not around early morning, a time switch may also be worth consideration.Greenhouse is 8'x10'

[JanG]

I too rely on a fan heater with a frost setting just for emergencies, ie. unusually late frosts, for the same reason - expense.

Heated cables in a sand bench are much more economical, especially as ancellsfarmer says, if you can build a polythene cover over some of it to create added protection and keep the warmth in. I imagine heat mats could achieve something of the same effect without having to have specially deep staging.

[Vinlander]

If you want a cheap reliable heater with good thermostatic control for background heat then an aquarium heater is a good option - but it needs to be in a substantial amount of water that won't dry out between checks. A big cool box with a propagator on top instead of the lid will put the heat where you need it most (propagators this size with thermostats are very expensive). You should also consider LED lighting - to get the maximum effect at lowest cost you need a timer that only extends the ends of the day, though some studies suggest that  having the light on in the middle of the night can convince the plants that time is passing twice as fast and they need to speed up (look it up. I'm not totally convinced, and it would annoy my neighbours).

Cheers.

PS. 5W (50W equivalent) GU10 spotlights are cheap and efficient, and can be mounted inside the propagator lid (through holes with the sockets outside) - you are trusting they are sealed but their main use is in kitchens...

You might notice penny-pinching is a bit of a theme for me.

[ACE]

I have just picked up a tubular heater from our allotment table that we use for freebie surplus stuff. Plugged it in and it warms up, wether the thermostat works will be another thing.

[Tee Gee]

You might notice penny-pinching is a bit of a theme for me.

As is with me!


One thing I did when buying my thermostat was to look at the manufacturer's accuracy statement!

Mostly I found that they would say something like +/- 3° but is this C or F?

Think of it this way ; 3 °C= 37.40000 °F  / -3 °C= 26.60000 °F which is range of 6 °C to 11 °F

So because I don't know if they mean °C or °F  and say I set my thermostat to 40 °F (4.44 °C) it could mean I could be heating to 43° F or 7 °C which means I am using more energy than planned, or worse still my temperatures might be too low.

So I spent a little more for a Thermostat that was accurate to +/- 1° thus making my system more energy efficient.

Then if you apply some other 'heat saving' suggestions the others have given it (IMHO) makes using 'Electric' more viable!

http://www.thegardenersalmanac.co.uk/Content/H/Heat%20conservation/Heat%20Conservation.htm

[ancellsfarmer]

If you want a cheap reliable heater with good thermostatic control for background heat then an aquarium heater is a good option - but it needs to be in a substantial amount of water that won't dry out between checks. A big cool box with a propagator on top instead of the lid will put the heat where you need it most (propagators this size with thermostats are very expensive). You should also consider LED lighting - to get the maximum effect at lowest cost you need a timer that only extends the ends of the day, though some studies suggest that  having the light on in the middle of the night can convince the plants that time is passing twice as fast and they need to speed up (look it up. I'm not totally convinced, and it would annoy my neighbours).

Cheers.

PS. 5W (50W equivalent) GU10 spotlights are cheap and efficient, and can be mounted inside the propagator lid (through holes with the sockets outside) - you are trusting they are sealed but their main use is in kitchens...

You might notice penny-pinching is a bit of a theme for me.

I sourced a STANLEY SXLS29322WE. dusk til dawn sensor which is adjustable to a light level of your choosing, and which will switch on/off to give power to a light within a set day length.Normally on at dusk , off x hours later or when the light level is deficient(such as a thundery sky). Capeable of switching 10 amps, thats a lot of lights! Was about £12 iirc. Stanley ean13  barcode 5 020024 901126

[George the Pigman]

Thanks for all your advice. I ended up buying a Simplicity 2kw heater with a thermostat and separate temperature controller.
I'll let you know how it works out.