Keeping a greenhouse warm over night using hot water?

[lottieguy]

Hi Ya, I don't think the hot water idea would last very long as greenhouses are very difficult to keep warm unless you have gas, electric etc. You then have to insulate an area or the whole g/h. I use mini 4 tier greenhouses with a fleece and plastic zipped cover on them. I then put one of those small frost beater run on paraffin in the bottom to keep frost at bay. It works for me but you must vent it during the day to stop fume build up. I watch the weather forecast each day and heat accordingly. The Victorians used to use hot beds and maybe that could be an option. Good luck

[Bill HH]

Sorry, maybe not the most constructive post but - why the big rush to sow things so early ?

Edit to add - this post was not necessarily directed towards the original poster.

I agree with this. Its the urge to get things going that grips us all, but in my experience it can be expensive and not always worth the cost. Things i planted in March / April get off to a flying start and usualy overtake the early planted stuff. Its not just the temperature its the amount of daylight that plays a big part. Some things can be grown, I have sweet peas, leeks and onions planted, but tomatoes will have to wait.

Its is the same if you start things in your house, the plants soon become leggy and have to go out into the cold.

[skeggijon]

If you have two or three immersion heater elements powered up in the water butt it might just work

[Kristen]

I agree with this

Me too ... excepting that you could get some nice C******s growing lights and make an early start ... gives me something to do in the Winter. Perhaps your local cop-shop has some going cheap?

[Kristen]

If you have two or three immersion heater elements powered up in the water butt it might just work

I started to do the sums, but it made my head hurt.

I thought perhaps 1kWh was enough for a cold-ish night in a small-ish greenhouse. e.g.a 2kW fan heater on for 30 minutes, cumulatively, during the course of the night.

Heating 1 cu.m. (1000L - e.g. an IBC) of water by 1C is a bit more than 1kWh (although my maths could do with checking!). So my question would be by how much a small greenhouse could heat 1 cu.m. of water, on a sunny February day (let alone a Sunny January day, and ignoring an overcast day ...). Clearly the bigger the surface area the better, and thus 1 cu.m. is going to be useless - but 250L raised by 4C would do the same job, that's about an average water butt, and a better surface-area to volume ratio ...

But I keep coming back to: what would I do on an overcast day when the sun has not heated by water tank and that is followed by a cold night - just let the plants die?

[Potstubsdustbins]

#18 A standard immersion is 3Kw 2 or 3 sounds a very expensive way to do it. Plus the cost of the heavy duty cabling to supply that amount of power, plus the cost of the electrician to put it all together. Starts to make very expensive plants.

[veggiechicken]

If a cold night is forecast I had the idea of putting a water butt in the greenhouse and filling it with really hot water (I have a hot water tap outside so can just use a hosepipe)

Do you think may work?

Potty, any idea how much the energy would cost to fill a water butt (?200 litres) with "really hot water"?

[Potstubsdustbins]

I will get me calculator out.

[Potstubsdustbins]

Say you start with cold water 10'C/50'F and raise it to 80'C/176'F you would require 55440Btus or 16.24Kws. if you were working in ideal laboratory conditions and not losing any heat during the process.

In reality my best guess would be about 20Kws, it would then depend on your tariff as to how much you actually pay.

The real cost would come as the thing loses heat and the immersion tries to keep pace, unless you switch the immersion off then of course come the coldest part of the night, in the early hours the container would be cold anyway.

[Potstubsdustbins]

Another way folks might find easier to understand. If you had a 25kw super high efficiency band 'A' combination boiler and you raised the water by just 35'C, so say from 10'C to 45'C it would take about 25 to 30 minutes to fill the butt.

[veggiechicken]

Thanks Potty. Much as I expected the answer to be. An expensive and inefficient way of trying to keep a GH warm

[Shadylane]

Sorry, maybe not the most constructive post but - why the big rush to sow things so early ?

Edit to add - this post was not necessarily directed towards the original poster.

Its odd as most people will say 'hold off, wait a while,' but most of my past regrets around growing have been that I didn't start early enough. Our first year on an allotment, I started parsnips in February. Our neighbours said 'oh that's far too early!' (it's his motto I think). Our parnsips were huge and plentiful unlike our neighbours which were few and far between. Since then I (possibly stupidly) listened to this advice and sowed later and have ALWAYS regretted it. I've never had the same success as that first year. The ground was too dry and they didn't germinate...or we had a freak week of early hot weather but the seedlings were too small to cope...or by the time I accepted they weren't going to show it was getting too late.

Same with brassicas. Last year I said 'no, I'm sowing later.' At time of planting out they were too small to survive the slug attacks and by the time they recovered, it was getting too late. So yes I'm going back to how I did things in my first and most succesful year and starting early. I use peat free compost and I find stuff grows much slower anyway.

One of the vets down the allotment has already got cabbage seedlings. Every year he starts ridiculously early and every year he has bumper crops. I know it depends on where you live and what you're growing, but for me waiting a while has always ended badly.

As for tomatoes... well the jury's still out on that one. We tend to start ours around now these days (as opposed to January) and they seem to crop earlier than others who start in say April. But I don't think there's a a difference in say January to early March.

[Kristen]

most of my past regrets around growing have been that I didn't start early enough.

I agree with you about cold hardy crops, like Brassicas, but the conversation started with Tomatoes, and I think they are less worthwhile starting early if all that is available is a windowsill, or an unheated greenhouse that is going to struggle to stay above 10C at night at this time of the year.

[Shadylane]

I hear you Kristen; my post was more in reply to Kevin, who seemed to be asking about sowing early in general, not just tommies

[Bill HH]

Well seeds are cheap enough, you can plant some stuff early and hope for early spring then if it fails sow some more.