Friday, January 07, 2011

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.  Add a switch so the blower will run when thermostat "calls" not when plenum is hot.
2.  Move power cable to back.
3.  Build intake airbox with filter holder.
4.  Internal relay box for status and remote command.


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.