[barbarella]

I have been using a tip I read somewhere and keeping my four large watering cans full of water in the greenhouse.  The idea is that they heat up during the day and give off heat at night.  I think it must help, although I can't prove it.  Of course, the bonus is that you don't risk giving your seedlings chilly water.

What does everyone else think?

[scabs]

I can see the thought behind it, but is the thermal output at night not negligable at best?

Sorry, don't mean to poo-poo your idea, which is interesting! 

[prakash_mib]

http://chat.allotment-garden.org/index.php?topic=51886.0
here you go.
discussed recently in detail. I once read a whole document about a man in north america with more than usual subsidised gas made a green house and used thermal mass.
What you are doing is right but it can also become cold mass instead of heat mass.

[digalotty]

if the cans are insulated this could work ,lay them on polystyrene to keep them off the cold ground and wrap them in something with good heat retention and it could lift the temperature just enouth to do the job , may need a little help on the coldest days though

[hamstergbert]

In one of those 'grand designs' programmes on the idiot-box there was one house in which a swimming pool in the basement was used as for thermal storage of daytime solar gain and solar water panel heating (as well as for the odd dip, one presumes) and was apparently quite efficient at smoothign out the temperature peaks and troughs.

[solway cropper]

Any container painted matt black and filled with water will act as a storage heater by absorbing heat during the day and releasing it slowly at night but I think you'd need more than a few watering cans. With a south facing lean-to greenhouse you'd have to cover the back wall to make a real difference. Back in the old days when I was a hippy this was one idea we looked into in our quest for self-sufficiency but, along with the wind generator on the gable end of the house and the hovercraft, it never quite worked as well as we'd expected 

[barbarella]

Yeah, I guess it's not such a ground breaking idea, but as they say 'every little helps' and I've got to keep the watering cans somewhere.  It's always nice to find them full when you need them and not have to traipse to the water butt or tap. 

I don't just rely on them for heat though.  I've got a a fan heater with a frost stat and I am putting fleece over the seedlings at night at the moment.  These sunny days and frosty nights are set to last for most of the month so the weatherman says.  Love the sunny days - not so keen on the nights

[sunshineband]

Any container painted matt black and filled with water will act as a storage heater by absorbing heat during the day and releasing it slowly at night but I think you'd need more than a few watering cans. With a south facing lean-to greenhouse you'd have to cover the back wall to make a real difference. Back in the old days when I was a hippy this was one idea we looked into in our quest for self-sufficiency but, along with the wind generator on the gable end of the house and the hovercraft, it never quite worked as well as we'd expected 

Using a body of water for heat storage effectively is about scale 

[bailey]

i did see a similar idea in a mag or could be on t net, i will try and find it,,

basically it was in a large poly tunnel where guttering or similar was laid around the beds and filled with water which as you say warmed up in the day, and supposedly kept the frost off on most nights aprt from the coldest,, but the same was used in summer for watering not sure how it worked though,, if i find it again i will post it as the watering idea was one i was thinking of trying in my own poly,