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Building a forced air composting system

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Step 2: Design & Setup

Picture of Design & Setup
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Again these instructions assume you already understand composting and building a compost building. For this project I recommend that your compost bin to be no smaller than 27 cubic feet, or roughly 3 feet wide X 3 feet deep X 3 feet tall and that you have two of these bins that are undercover or can be covered securely with a tarp to control moisture levels.

The set up I am working with up is a 7 foot wide X 15 feet deep X 5 foot tall with a 12 foot roof roughly the same width and depth as the average parking spot . By dividing this space in half, this will allow for a two bin system , each bin roughly 3.5 feet wide X 4 feet tall X 12 feet deep, with a rough capacity of 144 cubic feet per bin, which is generally just enough space for a months’ worth of horse manure for 2 large horses or 3 small-medium horses.

Once you have determined the permanent location and dimensions of the bin, map out the best and most efficient location for pipes to be laid.  When filled all of the compost should be within 18 inches of a pipe.

For me this was simple, just single, straight pipe the length of the bin. As the bin was 3 1/2 feet wide, the single pipe  down the middle, would be perfect.

Heated air will naturally rise so incorporate vertical chimney pipes help to aerate the upper layers of the pile and help to distribute heat more evenly through the pile. The chimney pipes will also help to direct moisture down deep to the center of the pile instead of lingering in the upper, outer layers.

When designing the system, try to keep the lengths of pipe the minimum distance you can. If your blower is 35 feet from the compost pile the force of the air will not have adequate pressure to push the air though the compost properly.

Design your system so that the pipes are cyclical or capped to help keep the air pressure up and the air directed properly.

Determine the size of PVC pipe you want to use. For small bins, less than 50 cubic feet in volume I recommend using 1 1/2  inch PVC pipe but anything larger I recommend 2” PVC pipe. I am using 2” PVC pipe in my setup.

For this build I used my leaf blower that I bought for $30 at Home Depot. It’s a no name brand that you can probably find for even cheaper on eBay. This blower is great for 18’ – 24’ feet of pipe. If you use more than 24’ feet of PVC pipe you’re going to need a blower with more power. I would suggest looking in to using a hot tub air blower.
 
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