Greenhouse heater

[Babru]

I have electricity in my greenhouse (brought into the garden by the last owner, not paid for by me!) I have been running a heater overnight for the past couple of weeks, set to 7 degrees ie it comes on when the temperature dips below 7. As it has been sub zero, the greenhouse has then been kept between +1 and 5. However - OH has been looking at the cost, and it seems prohibitive to run.

I'm wondering about paraffin - anyone any experience of this? Recommended heaters?

It's only for a short few weeks in spring, when the weather catches me out with a greenhouse full of tender seedlings and dahlias.

[burnie]

I used to use Paraffin some years back as I had a free source of it, I found the heat "wet", lots of damping problems, an electric heater tends to dry the air more. What I am thinking of doing is using low wattage soil heating cables to warm up my blowaway inside the greenhouse rather than trying to heat the whole greenhouse. Because a glass house is not efficient at retaining heat, your electric heater is probably running all night.

[quanglewangle]

I use heat cables successfully although the cold spring has caught me out this year.
My greenhouse is monitored closely for temperature and my experiments in the past have put me off space heating.

In no wind a 500W heater will raise the air temperature of my greenhouse only about 3°C about the outside temperature.
In any sort of wind I am lucky to get 1°C difference over outside due to drafts.
YMMV

A combination of in-ground heat cables and night-time fleece covering on frosty nights seems to work quite well.

Having said all that I am thinking of installing a 500W to come on at 7°C to protect my aubergines

Graph shows last night, when I did put a 500W heater in the greenhouse. We had a light grass frost and outside air temperature of about 3°C
The blue line is greenhouse air, red is aubergine pots, purple is tomato bed



I am in the extreme south west of Cornwall so pretty mild here usually

[nickdub]

I've used a paraffin heater for a few nights so far this year. I've had the heater for ages and someone gave me some paraffin they didn't want, so I thought why not ? It may make the difference of a degree or so in my poly-tunnel, but it is a bit of a pain to clean - I certainly wouldn't buy a new one.

[Mark Rand]

I have an electric heater for one greenhouse and a paraffin one for the other, although I haven't used the paraffin one yet this year. Kerosene at 60p/litre is a lot better than the ripoff price for most modern paraffin.

[Babru]

Thanks very much everyone. I don't fancy the damp and dirt produced by paraffin as people have suggested. I do think that some kind of enclosed structure within the greenhouse might be a better way. I have a frame I use for my quadgrows in summer, maybe I could rig up bubble wrap 'walls'.

Something to work on for next spring.