Foundation Box top view

Here is the top view of the insulated "foundation box". The bottom will also be fitted with a piece of 2" insulation. 

4" perforated corrugated drain pipe will be placed at the bottom, which will receive heated air blown down from inside sun heated air at the top of greenhouse. 

2ft of1.5" rough stone will be placed on top of the perforated pipe and should soak up and store any temperature from the heated air passing through it.

Lower Foundation Box

I made some progress over the past few days. Here you can see the sub-grade insulated box within corner post and sill cap. The posts are 2"x6" p.t. lumber, 32" tall screwed together in an L shape. The sill is made of 2x4 p.t. lumber over posts. 1x5 p.t. lumber is screwed/glued to the outside of the sill to act as an attachment point for posts and frame to be built above.

Cross section of air temp controlled air flow

So in theory this might work. The fans are advertised as waterproof 12v computer fans. Rock isn't the greatest heat storage material, water is but I'd have to include an air to heat exchanger and a water tank beneath the wicking/grow bed. That would break my budget so I'm going with 1.5" dry stone as a winter heat sink.

Air Temp Control Heat Sink Overview

This is the plan anyways. At this point.
2 fans $20 each, 2 monitoring boards $6 each. Wood insulation $20-ish.

The Hole...

After many wheelbarrow loads and one small cave in...

This is the hole for the heat sink, 34" depth, 4' wide x 2.5' front to rear.

 Four 16"x16" concrete blocks leveled in the corners are the footers ready for the 4 pressure treated posts.

SketchUp sketch design

Hello folks, this blog is to document a semi quick build of a 4' x 2' winterized greenhouse. This is the basic mockup done in SketchUp. I plan on including a heat sink below the grow bed which will draw any excess internal warm air down into a dry rock bed beneath the grow bed. I also plan on adding a water bed heating pad just below the grow bed (just above the rock heat sink). I also plan on building a wicking bed into the design and hand water/ fertilize the plants allowing them to soak up nutrients and water as needed.