Hi Bjs you really need an electric greenhouse heater. Paraffin heaters put out moisture as well as heat and this can create problems.

I had a paraffin heater last year in my greenhouse. What a disaster! Black smoke everywhere in spite of my fastidious attention to the wicks. There was continual wet everywhere...awful..don't do it, get a little fan heater like mine, much better! :)

Thank you both for that it was what i half suspected,
I have had electric in there in the past but its a fair job to rewire, its near a hundred feet from the supply.
Suppose I will have to do it.
Thanks Brian

welcome! :)

I have a very old paraffin heater, but I am going to change it next year as it is either on or off and you have no control - paraffin is expensive. Electric heaters on the other hand usually have frost protection / thermostats and timers so give you more control.

Thanks Kfunsters
I think we all need all the control we can achieve over how much energy we use.

May I ask what you grow in your 'alpine house'?
I have one, well 2 really, and in neither of them do I have heat, In fact most of the time the doors at both ends are wide open and in the true alpine house, there is no glass in the sides only in the roof, so no way of heating it. -8c is fairly normal for us, most winters over the last 10 years have reached that, in the house itself never mind outside.

True Owdb our alpine houses are never heated and have air through them all year.

Owdboggy
sure you can ask, its the bulbs and corms that are suffering, snowdrops ,Cyclamen, dwarf Narcissus and to me surprisingly Anemones all of which require to be damp not wet, after a prolonged period frozen the roots are damaged.Cyclamen Coum is particularly badly affected as Is Creticum ,but that must be considered border line hardy anyway. Cilicium and libanoticum are unaffected, Coum in the garden is OK.I have lots of snowdrops in the garden and troughs all alright but four varieties duplicated in pots are very sorry sights,I have now removed two lots and the bulbs are rotten.Quite a few of these items i have grown for a good many years and up to 2010 there was very little problem.I think even sharper drainage may well help ,but not convinced it will be the total answer if we have another winter like the one we have just experienced.I will be interested to hear your comments.
PS the cyclamen corms are firm its the roots that have died, its easy to see they come away with no live white parts to be seen.
Brian

moon grower
there is no problem with my collection of Drabas Lewisia's & Primulas and the like, and as you both say doors and window in the past were rarely closed.

Have you tried simply covering things with fleece when the temp. drops seriously? That is what Bulba does and it mostly seems to work... though we do still have loses.

Moon grow
Yes i used it from some time in November for the first time, and in the area where the Cyclamen are the leaves did not collapse as much,so foliage wise i think it is a help, however the staging is raised with the pots either part buried in sand or standing on top so cold was able over the extended time it was frozen to penetrate from the bottom.( this is the difference with things in the ground the cold does not come from below)This takes me back to the original question and if i could achieve 0C throughout the houses when we have prolonged frost would it be cost effective.
If i do it i think it has to be electric.
thanks Brian