Well today is below zero for the first time this fall, December 9th, 2011.
The greenhouse  is heated with a wood air tight furnace with forced air draft, temperature of water at 110 , shuts off the blower until the temp drops 5 degrees.

The water circulates into the greenhouse, first through a heat exchanger to heat the potting room, then into the finpipe under the potted plants.

 A temperature probe in a pot of soil, regulates the opening and closing of a valve, so the plants don't get too hot.  Soil temp never gets up to 60 in the winter.  Plants like it cool, I get chilled as the air temp is much cooler. 
Today is forecast for sunny and warming up.  I can then work out there keeping the plants happy.
The barrel is growing a potatoe or two and last week I put Leeks in there.  They should like the cool weather and produce some edible plants in a few weeks.

Meanwhile I anticipate more veggies from the cool realms of the winter greenhouse.
My favorite at this time is Swiss Chard which is 2 seasons old.  I continue to harvest when I need some greens.  I expect it to bolt one day, but so far so good.  These plants are from the seed mix called Bright Lights.

One more picture before I finish today, (I am making up for 2 years of neglecting this blog)

This is 2 parsley plants growing in the ground bed.  there's enough here to keep my Spaghetti sauce flavored  and my breath fresh for a year.  I nibble it fresh, just like a rabbit.