Keeping things warm in a cold greenhouse

[dod]

I have a problem that I suspect many others also have, mostly when when growing seedlings. It is warm but not very sunny inside the house, whereas it is cold but much brighter in the greenhouse. I don't have any power in the greenhouse, but wondered if I might be able to run a heated propagator out there.

Would it be possible to run one from a battery, using an inverter to give mains voltage? It would need to be able to run for the best part of a week without needing to recharge the battery for it to be practical, and might need to have to power a propagator of up to 50W in order for it to be big enough to be useful.

Does anybody have any views on whether or not this might be practical?

Thanks in advance...

[Potstubsdustbins]

If my calculations are correct and thats not a certainty, it works as follows.

If you have a 12volt 80 amp hour battery you would get a battery drain of approx 4 to 5 amps an hour to get 240volt 50 watts therefore you battery would last 20 hours at best. A thermostatic control would extend this but by how much I know not.

Looks to me like calor gas or paraffin.

Potty

[veggiechicken]

Could it be on a timer as well - just come on for a few hours a night?
And is your GH insulated with bubblefilm?

[Alison]

What are you wanting to grow in there? To be honest I've given up heating mine now as I find things grow so slowly when it's properly cold that it's just not worth the feeling that you're getting an earlier start. When it can be useful though is to protect against late cold snaps.

[SarzWix]

I managed to keep things growing in a cold greenhouse last year by putting corrugated cardboard under the trays and then wrapping two layers of fleece around them too. That protected lots of tomato plants from sub-zero temps. But, I don't think it would have worked this early in the year because of the low light levels. I also have a propane powered greenhouse heater, and that's very efficient, works on a thermostat, and is cheaper to run than paraffin or electric, but cost about £100 to buy...

[dod]

Thanks Potty,

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)

Am I missing something crucial?

I'd rather not go the paraffin heater route because I would surely end up heating the whole greenhouse slightly, rather than a small part of it to a more comfortable temperature. I tried this last year and wasn't terribly sucessful, I assumed because whilst the air was slightly warm, the soil that the plants were in wasn't. Growth was consequently very poor, perhaps even negligible.

I was thinking it might be a way to help things along in March/April/May time, rather than this time of year.

[Two_Sheds]

it might be a way to help things along in March/April/May time, rather than this time of year.

You don't need extra heat or light once the days are longer (the time you mention). Hardy stuff can get started in March, with the more tender veg (squash, corn, beans) being sown late April or May. No lecky needed

[Kristen]

For the things I want to start earlier I work on the basis of providing the light they need, in a nice heated, insulated, house rather than trying to heat the greenhouse - which might have lousy light anyway, or absolutely Arctic temperatures, depending on the weather

Depends on your budget, of course, likely to cost about £80 - £100 for a lighting rig which will cover about a square metre. The Cannabis forums are full of very useful information if you want to research growing indoors with artificial light.

200 Watts on a timer for 7 hours a day over 4 winter months is about 170 kWh which, at 18p per unit, works out at around £30 of Electricity. I'd be hard pressed to heat a greenhouse with Paraffin or Bottle Gas, or even Electricity, for that - although I think that those type of heaters are a viable / cost-effective proposition to heat in Spring on nights where night temperature might fall below 10C.

Delaying, as Two Sheds says, until the light is better is the best option ... but I get itchy fingers by late Autumn, never mind the New Year!

[Madasafish]

I electrified my greenhouse this year - well end 2012 - on the cheap after bubblewrap/replacing seals for door and stopping leaks.


Circuit breaker (LCD ) on mains outlet plug (had already )
Temporary 50 meter cable. (£39 less 20% B&Q) nett £32
Terminated in waterproof circuit box in greenhouse. £20
Used 2500 watt electric heater ebay £29
Electric thermostat ebay to control temperature £36 (was £60)

Cable protected - when laid - by surplus water hose split down center. (had already)
Waterproof plugs in greenhouse £7 ebay


Total £124.

No qualified electrician required as not permanently connected to mains . Remove in summer when not needed. Not currently installed cable so nothing to see.

(Permanent connection cost a fortune as 35 metres from house- greenhouse)..

Fed up with paraffin smell and lack of control (20 years)...



Worth considering...

[Kristen]

For anyone with/considering an electric heater I strongly recommend a high quality thermostat. Electricity has much better opportunity for savings by using an accurate thermostat than, say, bottle Gas heaters which have a very crude thermostat - and Paraffin heaters usually have no thermostat at all.

Cheap thermostats will overshoot the target temperature by as much as 10C which either costs a fortune or, if it undershoots by 10C, results in dead plants

A good quality thermostat with very narrow hysteresis is going to be £50 or more, but should pay for itself in a season, two at the most, by not overheating the greenhouse.

[Urban]

how about adding a wind turbine generator and maybe even a small solar panel to keep your battery topped up? pretty cheap to buy on ebay

Ive thought about doing it myself, my propagators are only 8watts (*2) and have a 25watt energy saving daylight bulb

[BertieFox]

Just having one of those 'Is it worth it?' moments. Last night we had minus seven or eight and I've just checked inside the polytunnel.
I had made a nice 'snug' area on the staging (or so I thought) with a 4ft, 240 watt tubular heater and a 'tent' of polythene covering it all up. I had a lot of seedlings in modules in there but discovered that most of them froze solid during the night and were blocks of ice. Only the ones right next to the tube were ok. The temperature right next to the tube was only 9C at 11.30 today (French time).
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.
Short of spending a fortune is there ANY way to protect tender seedlings or tender plants through winter? Every year I try and most years I fail!
My next experiment is going to be building a "solar greenhouse" facing south with a thick rear wall, and lots of drums of water against the wall to act as a 'heat sink'. However, I rather imagine in conditions like this I might just end up with drums of ice instead!

[Aberdeenplotter]

Short of spending a fortune is there ANY way to protect tender seedlings or tender plants through winter? !

Do as the Victorians did and create a humungus hot bed using horse muck. problem is it runs out of heat eventually and needs to be replaced. No problem if you have a source and easy access and mechanical loading and unloading. Easy said eh

[Madasafish]

I just do not bother with anything in a greenhouse before March. For exactly the reasons given by Bertie Fox..

Except last autumn I sowed sweet peas . They are inside a mini greenhouse, inside the insulated glass greenhouse. It's being sub -5C all this week...


Heating just now is a waste of money so I don't start sowing anything till Feb..

And yes I have a good accurate thermostat!:-)

[Two_Sheds]

is there ANY way to protect tender seedlings or tender plants through winter?

My tender seedlings (pelargoniums, fuchsias, early sown tomatoes etc) are in the house, on cool windowsills.

I don't put anything tender in the unheated gh until the worst frosts are past (mid March for me).