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Garage Furnace

Installing a mobile home downdraft furnace in a garage

A guy at work gave me a great idea to find a used mobile home furnace to use in a garage.  This is great as  they are super cheap when picked up used, I paid $120 for this one.  The one I got a hold of was a Century FG80C2 downdraft Natural gas furnace. 

Things I'm going to change/add

1.  Move power cable to back.
2.  Build intake airbox with filter holder.
3.  Internal relay box for status and remote command.


    Heating and Cooling by Time Life Books (don't have the ISBN this book is too old (1967))
        This book was amazing!  Showed everything with great illustrations and detail.  
            Showed me 
                the wire color coding to the thermostat
                general maintenance
                how to clean a gas furnace
                adjust the burners and pilot light... everything a must have book.
                Etc etc etc...


    I measured the base and found concrete blocks that would match perfectly.  I wanted this a bit higher off the floor as the bottom will have air blowing out of it.  I did not glue the base down or use anything to hold the blocks to the floor of the furnace.  

    Once it was atop the base and mounted I started to measure how I wanted to run the flue.  This was pretty easy as I wanted to exit the flue through the wall and not the roof, for many obvious reasons.  

    Gas line was proflex CSST that was put inside burried electrical non metalic conduit.  I put in a gas shut off before the CSST and right before the flex hose to the furnace.

    Electrical.  Installed a 15 amp breaker as thats what was rated for this furnace and should handle any additional electronics for control.


Gas line.

  This was something I planned for months in advance and ran a non metallic conduit that would house "Proflex CSST".  This is Corrugated Stainless Steel tubing.  This made it possible to easily make the underground run and not have to try and fit black iron pipe together and then worry about how long it will last from rusting underground.  
  Even though you can re-plumb an entire house gas system with this stuff, there was something I learned about it when I was reading the product installation and sizing primer.  You can size this just like normal BIP, but the mfg. recommends sizing up when using something like a fireplace or when noise could be bothersome as the pipe's corrugation make the gas "howl" or "hiss".
*update* 1/17/11 This didn't turn out to be the case.  I have run this system for about 4 hours, no such noise nor problems have arrose. 

   Finishing up installing the gas line.  To elevate it from the floor a bit, I'm going to use cement blocks.  This should help it from blowing air right on the floor causing it to stir up dust. 
   I searched for quite a while online.  I could not find anything about this furnace.  Just so glad nothing is really different about these things even through the years.  I'm going to guess this thing is from the 60s from the use of hammer finished paint and can't be earlier as the use of vinyl power cords and not fiber wrapped like in the 50s.
   Something I have been drawing up is the use of relays to have a remote switch in the house with a status light.  This same system idea will also be in use to turn on the air compressor in the basement.  This system will be very easy to implement as I ran a 25 conductor cable from the house and the garage.  The use of terminal strips are a must for easy expansion and reconfigurability. 

  When Wiring this up, I found the "fan" control from the thermostat didn't work as it should.  Since I'm just using a SPST switch for the "auto/on" fan control I knew something was up.  When I took the Panel off inside the furnace. seems someone removed the fan relay and did some modifications.  Owell, this is kind of in my favor as I want to add more relays to the basic wiring anyway. 

  Ordered new relays from McMaster-Carr, 24vac than can handle 16amps at 120 which is perfect for the fan relay.  Another is going to be wired in parallel to the electro gas valve to give me a status light when it is "heating".  The third relay is for making when the fan should be kicked on.  IE all furnaces start the fan after the plenum have reached a preset temperature.  This will allow the fan to kick on when the thermostat "calls" for heat this will help remedy the massive oversizing of a furnace for the space as it will slowly heat the plenum, this in turn will slow down the "cycling".  Still finalizing some of the schematics or I would post them.

  Furnace is installed and running, now that it is heated in there I can work on the more fancy wiring.

  After using the system for a bit now.  It turns out that this is not oversized for the garage, but nearly just right.  Currently working on the homemade wired remote control system.  Pictures, digrams, schematics will be added when completed.

  Schematics in seemingly final spec V.03.  Revising to "compartmentalize" how wires and parts will be routed.  No real difference from V.02 other than moving stuff around and where to put what things in what box.  This final version will house all the mods and circuitry in one "aux" box not several spread around or ext ones that were originally drawn up.  Remote control "panels" drawings schematics also finished.  Idea for an additional "low temp/Anti-freeze" thermostat is considered and appropriate circuitry has been added, but decidedly not added to remote panels.  

  This was placed on pause since it is functional and near full disassembly would be required to upgrade it.  So this will be done once it is nice out.

    Slight tweeks in design and control system.  Most parts are acquired.  When I finalize the design I will upload it.