Keeping things warm in a cold greenhouse

[Alison]

In the tunnel itself, all the beetroot leaves were flagging and a large calabrese plant I had great hopes for in spring looks badly affected.

I've shoved extra calabrese plants in the tunnel borders most years (ones that were rather pot bound in 3" pots and who's brothers were planted outside in the summer for autumn harvesting). They always survive OK (even in the two very cold winters we had a couple of years ago) and produce a nice early crop in about April-ish. They do tend to look a bit droopy when there is a heavy frost but I just ignore them for the winter (only watering if the bed looks very dry), feed in early spring and enjoy. I'm not saying yours will defo do OK but you might be surprised although am not sure if your's are in pots as I think that might well be too much for them if the whole pot freezes as oppose to having the volume of the border around them if you see what I mean.

Forgot to say, my tunnel has never been heated and at times somebody visits the tunnel to have a crafty fag, no idea who but if they're going to I wish they'd remember to close the door at this time of year when they go!

[Pa Snips]

I tried to do some sums - assuming that Watts / Volts = Amps (from W=V.A)
50W at 220V would result in a current drain of about 0.25 amps per hour
Accounting for the inefficiency of an inverter this would probably be closer to 0.3 amps per hour
So 1 Amp hour of battery capacity should give me about 3 hours of running time
This suggests that a 45 Amp hour battery should last about 5 days
So an 80 Amp hour battery should last a week (with a little spare to cover whatever non-idealities might exist)

Your calculation looks fairly accurate to me but at 45Ah you would be looking at using a small car battery. The problem with this is that car batteries are designed for short bursts of fairly high drain - such as starting a car. What you would need is a leisure battery, which is designed for long-term low-drain usage, they also start at around 85Ah so would last much longer. Even 110Ah batteries can be bought for a little over £60.00 if you shop around and should, theoretically, last a couple of weeks between charges.

[Hothouse]

This is my solution to keep seedlings warm in the greenhouse



its a coldframe sitting on the bench with a paraffin heater underneath , it does a great job.
I got electric in last year so am considering

[Hothouse]

I am considering putting a heated mat instead of the parrafin heater with a similar cover. The little tin plate is to stop water from dripping onto the heater and also from melting the polycarbonate lid.

[Madasafish]

I have been running my electric heated greenhouse for 4 weeks now: see posts earlier.

Weekly running costs average £5-50 - cheaper than paraffin. Min temperature 8.5C

Heated propagator in g'house germinated tomatoes which are now growing in tubs in greenhouse .

Ditto other seeds.

Insulation makes a huge difference..