Replies

1. 
   JohnWW | Oct 18, 2006 07:30pm | #1

   If the slab is properly insulated for radiant heat, it shouldn't be all that cold during the summer since the insulation under the slab should keep the concrete from cooling down to ground temperature.  If you used plastic drain pipe for the ducting it would also provide some additional insulation and would thus run warmer and wouldn't rust through if some moisture did condense out.

   There are both plusses and minuses to running the ductwork in the slab.  The big advantage, of course, is that the ductwork is out of the way and not running up to the ceiling in the middle of the room where it interferes with moving long boards around and creates a lot of visual clutter.  A second advantage is that a slab system is often more compact and has better airflow but this depends on the design.  An under the floor system is usually quieter too.  If you put the ductwork in the slab, you should also install the electric power for the machines in the floor at the same time to get the wiring out of the way.

   The down side of placing the ductwork in the slab is that it becomes fixed in place making it difficult to reposition your machines or to add a new machine.  The best set up has a full basement or at least a heated crawl space under the shop so that the system can be built out of conventional pipe that can be reconfigured from below if machines get moved around.

   There are various ways to make an in the floor system more flexible and serviceable when there isn't access from below.  

   One way is to install a wood floor on joists over the slab with removable floor panels that allow access into the joist space to run and service the ducting and wiring.  This set up is obviously more expensive, but allows a lot of flexibility and gives you a more comfortable floor to stand on, and one much more forgiving to dropped tools.  I would presume that a set up like this would somewhat restrict the flow of heat from the radiant slab but it might still work since radiant is often installed under wood floors.  

   Another approach is to create a branching system of open concrete lined channels in the slab at the time it is poured.  Later, the duct work and wiring can be installed in the channels with removable plywood panels covering the channel after the installation is completed.

   John White  

    

   
   

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   Edited 10/18/2006 12:36 pm ET by JohnWW