Allotment Gardening Advice Help Chat

Growing => Growing in Greenhouses & Polytunnels => Topic started by: jjat8cv on December 03, 2012, 18:30

Title: Heating in a polytunnel
Post by: jjat8cv on December 03, 2012, 18:30

I read somewhere that  bottles of water put in a polytunnel in winter will warm up in the day time and help keep the temperature up a little during the night. Has anyone tried this? I was thinking of using two litre bottles filled with water to edge my polytunnel beds to take advantage of this but am not sure if it will work.

Title: Re: Heating in a polytunnel
Post by: mumofstig on December 03, 2012, 18:48

Neither am I - it was -3C in my greenhouse a few nights ago, so the water in the bottles would freeze, no matter how warm it was during the day.

Title: Re: Heating in a polytunnel
Post by: AshtonValer on December 06, 2012, 09:12

Small bottles wouldn't retain heat. I'm looking into two options:

a) a section of water-filled plastic drainage pipe (black will absorb more heat during the day) that can be set upright in the poly/greenhouse. Needs to be fairly big to retain heat longer. You could also use an old iron radiator, painted black, in the same way - or jazz it up with a solar pump to distribute the heat around some piping


b) - slightly more technical, but can be done cheaply with some recycled materials, a gravel heatsink. Can be jazzed up with a timer/solar panel/temp sensor switch

  Dig a pit, stand a pipe in it and then fill around with pea shingle. Fit an old PC fan at the top to push warm air down from the ceiling of the GH/poly into the gravel. Side benefit is the moving of air and moderating the overall temperature.

   The gravel heats up, then slowly releases the heat during the night.

Title: Re: Heating in a polytunnel
Post by: grinling on December 07, 2012, 16:18

what are you growing in the polytunnel?
Charlie grows lettuce over winter with no heat except sun. Mine has no heat except sun and I have spinach and swiss chard for the chooks in there.

Title: Re: Heating in a polytunnel
Post by: Amilo on December 16, 2012, 11:34

It's not a new idea, but in days of old, if you wanted a heated cold frame you dug out a 2 or 3 foot deep trench, filled half of it with fresh compost, IE new horse manure then put the soil back on top and the composting heats up the soil.

Title: Re: Heating in a polytunnel
Post by: shaun on December 20, 2012, 20:43

-5 in mine last week so putting enough heat in there would be expensive, plus there's the lack of light during the winter