greenhouse heating

Hi everyone, not sure where to post this so opted for this section , if i,m wrong please feel free to move.

I have an 8 x 12 foot glass greenhouse, I want to over winter my fushias and geraniums. ( oh and new potted lime tree ) I bubble wrapped last year and bought a parrafin heater but everything was very sooty, plus i knocked it over once whilst alite !! hubby not pleased as he thought i had set fire to myself as all he could see from the house was smoke and an orange glow ! anyway no one hurt so everything ok. because of this he has suggested we install a radiator (cental heating ) running from his work shop to save any more misshaps, pipes all laid just need to hook up.
But what tempeture should the greenhouse be kept at ?and what size radiator ? I should mention that I would like to try and start my seeds off in march next year as this year everything was a bit slow.does anyone have any ideas ? thanks 

When I kept fuchsias and geraniums I over wintered them in the greenhouse maintaining a minimum temperature of + 5C. Its best to insulate your greenhouse with bubble wrap in order to minimize heat loss and if possible partition it off so that you are not trying to heat the whole area. You will need a heat source capable of maintaining a minimum temperature throughout your greenhouse. Therefore during extreme cold conditions you may need a fan to disperse the heat from a radiator if you choose to go this way. For guidance in my 8 x 12 greenhouse I had a 3KW thermostatically controlled electric fan heater which just about coped during sub zero temperatures.

Cost wise it is difficult to determine as it all depends on the ambient air temperature but if the weather conditions are anything like last year it will cost well in excess of a hundred pounds to heat an 8 x 12 uninsulated greenhouse.

I used to have 6 huge standard fuchsias in excess of 20 years old and I had no other means of over wintering them except in a heated greenhouse. However over time they eventually died and I concluded it was to costly to heat the greenhouse throughout winter for my few other plants and therefore I now only use it in early spring for starting off young plants.

Another option for you is to take cuttings now from both your fuchsias and geraniums, pot them up or leave them in trays and keep them semi dormant over winter then start them growing in spring. Again you will need a frost free area but this can be in a relatively small area or in a large propagator although you need to keep an eye on the humidity as if it gets too damp the plants can start to rot. Alternatively you can keep stock plants over winter and then take cuttings from them in spring. Spring cuttings will quickly get going in the right conditions and will be large plants come the time for planting them out. You can, I believe, wrap plants up in newspaper or similar and over winter them but I have never tried this so can't advise.

Relating to your question on getting seeds going I use a heated bed in my greenhouse using electrical heater cables and a thermostat and get great results with seeds that need say a constant 20C for good germination rates. You need to be careful though not to sow seeds too early preventing you planting them out later on because of the risk of frost. The heated beds are also great for getting cuttings going. If you want some info try - www.thermoforce.co.uk. I use one 75W cable in a 0.85 Sq. Mt. bed of which I have 4 off and 2 thermostats controlling 2 beds each (if that makes sense). A lot depends how many seeds / plants you want to get going, if only a few then a small off the shelf electrical propagator will suffice.

Food for thought! Hope that helps.