Polytunnel warming... is this a crazy idea?

With the cold (!) summer days coming to an end, and my full size polytunnel up, my thoughts are turning to the next project!
The prospect of fully heating a polytunnel over winter are impracticable in the extreme, however what about raising the temperature in a section only?
My thoughts are along these lines. Create a section (non permanent), lets say 10ft (as the hoops are 5ft spaced) wide by 6ft deep, using polythene and/or large bubble wrap. To provide the heat source I've already acquired an old fully working Parkray style fire with integrated back boiler from a friend who was having it ripped out, piped in underground from a metal shed (again the skip rat in me go my hands on one of these for nothing, just needed dismantling), when I built the tunnel I buried two large sections of drain tube forming ducts for any future water or electric access I wanted. I think that I can lay my hands on some pipework as used in underfloor heating that could be used to form a heater matrix. Assuming I ensure the pipework underground and through the ducting and shed is sufficiently insulated, a circulating pump wired up in the shed with the fire would keep the system flowing.
With a free(ish) supply of logs and wood to burn, this would allow the water in the system to be heated and thus warm the insulated section to allow me to bring on plants that little bit earlier. I've already built a large heated propagator (http://gardenerscorner.co.uk/forum/threads/diy-propagator.46042/) which would be used for germination and getting thing past the seedling stage.
My though is that this would allow me to start of crops (chillies for example) that require a long extended growing period that we don't have the luxury of in the UK.
Any thoughts, or am I just loosing the plot!

 

Sounds good. My seasons are almost all solely chilli growing seasons, whats on your current growing list and what do you have planned for next season?

 

I can see where you are coming from but you need sunlight for the chillies too, with warmth they will grow very spindly in the winter months, and will get attacked by anything that fancies a bit of fresh greens.

 

Fair point. Maybe, a little scratch and rethink, before forging ahead with that one. Successfully brought a decent quantity on early this year in doors, with good bushy stock ready for a heated greenhouse very early April.

 

This season has seen all sorts on the go, from my list on the computer (I think there are some more!)
Anaheim, Chocolate Bhut Jolokia, Bhut Jolokia, Bolivian Hairy, Bolivian Starfish, Cascabel, various versions of Cayenne, Dorset Naga, Douglah, Fatalia, White Habanero, Red Habanero, Hot Lemon, Hungarian Apple, Jalapeno, Krakatoa, Maules Red, Poblano, Satans Kiss, Scotch Bonnet, TSX0525, Uba Tuba
Next year will see an expansion of the above, plus more varieties of the hotter end of the scale. Viper Naga etc. not really drawn up the plan yet.
Will also be growing some of my other favourite unusual veg such as more Exploding Cucumbers (they where great fun last year, but missed this years season!), Gooseberry Cucumber which when pickled look like picked aliens!), and anything else unusual that takes my fancy... always nice to raise a few eyebrows and laughs with the unusual stuff.

 

Too true. The sad truth is that the techniques they employ for their exotics(!), is ideal for chillies. The good news is when they get busted, or think they are going to be, the really daft ones dump the kit on the likes of ebay. I managed to get four 50cm x 30cm heat pads (run up to 32c) for £10.50 deliver. These will be ideal to keep a gentle bottom heat on some of the overwintering chillies.

 

you can build a cfl and reflector lighting rig pretty cheaply. Depending on the space you need to fulfil its cost effectiveness for less than 50 quid. I run this size system, with reflectors and ive never had too bad results...of and its only 100w all in all too!!

 

If you want to heat a greenhouse / polytunnel then the first money should be spent on insulation - same as with a house, it will pay back more over time. If you have free fuel then that translates into having to stoke the boiler less, and on fewer nights, and having less worry about whether the loaded-fuel/heat will be sufficient. One cold night when the fire goes out etc. can be total plant loss.

The biggest issue with light-your-own greenhouse heaters (including Paraffin) is that you have to light them when you think it will be a cold night, and they produce heat, and eat fuel, during the mild part of the night too. If you get caught out by a cold night (and haven't lit the stove) then you are hosed :(

Thermostatic control much better, and will only use the minimum fuel needed - so "less".

I think the best way to overwinter plants is indoors, in an insulated "indoor growing room", with artificial light. I have a Meta Halide lamp in my home office, but an (insulated) section of the garage, or loft, will be fine. As JWK said, all the information you need about the mechanics is well debated on the Cannabis forums.

Each 100W of light, run for 7 hours a day, over 4 winter months, is about £15

A story you may not have read here, and which started me off, was hearing on Gardeners World that you can get Cannas to flower in their first year if you sow them in September, but you need some lights. So I bought mine. Sown in September, Flowered in December - so they were right about first-year flowering! - and set seeds in January

 

Is there anyway you can make your propogator mobile? Put some wheels on it so it can be used in it's current position but then in winter can be moved into the tunnel to heat a small well insulated space, the space would be much reduced in size of course.

I know my 8ft x 2ft heated propogator (http://steverandles.co.uk/alottment/?p=533) actually raised the temperature in my 8 x 6 greenhouse earlier this year and I plan to lower the height of mine to give a larger growing space above over the winter.

Maybe it's feasible to utilize your propogator this way?

Steve...

 

I did a similar thing last year and put a blow-away tunnel in my conservatory and hung a grow-lamp in it for both extra light and also heat enough to keep temperature 10C+ (in Spring, not in the depths of winter! in Feb I had difficulty keeping it at 0C when we had -16C outside!)

Pics in this thread: http://gardenerscorner.co.uk/forum/threads/keeping-seedlings-warm-at-night.41357/page-2#post-522943

but for insulation it would have been better to cover it with bubblewrap, rather than polythene.

 

Sadly the heated props a little to big to move, also it's attached to the wall to take the weight of the sand used to retain heat. I could however build a smaller version for use in the tunnel.