Replies

1. 
   BKCBUILDER | Dec 27, 2005 06:32am | #1

   Pretty easy and inexpensive...put in the exchanger(put it in above or below the a-coil of the air if you have it(not in the return if possible), at your existing thermostat you'll add another stat for the solar. Take the "green" old stat wire and add a short piece to the "R" terminal on the new stat(old is still hooked up, this is a jumper to the new), and from the "white" old stat terminal to the "W" on the new stat.

    Now the new stat controls the fan blower, set the temp on the old stat a few degrees lower than you want the house(I'd say 4) and the new one where you want the house to be. If the house gets to the old temp...gas kicks on.

    Pull the disconnect on the outside air unit, or on a sunny day if the water gets too hot, the air will actually kick on due to high temps in the plenum( 140 or so).

     Happy warming!   KeithC

1. 
   DanH | Dec 27, 2005 07:31am | #3

   Note that it's best to have an isolation relay between the two stats you describe. This is because a heating/cooling thermostat may short together the fan and AC wires when the "fan" switch is not on. This would result in the AC coming on when your second thermostat attempts to operate the fan.

   If ignorance is bliss why aren't more people

   happy?

2. 
   DanH | Dec 27, 2005 07:26am | #2

   Most forced air furnaces have provision for a relay to turn on the fan when the AC is running. It is fairly easy to use this relay to turn on the fan under other circumstances, or use another relay parallel to this one.

   It takes a bit of "relay logic" in some cases to get it right. In your case, simplest would be something like a heat pump thermostat -- one that has two setpoints a few degrees apart. Or dual thermostats could be used. Then another water temp thermostat somewhere in the hot water line.

   Rig it so that if the temp is cooler than the upper setpoint (but not the lower), and the water temp is hot enough, the fan is turned on. But if the lower ("emergency") setpoint is reached or the water temp is too cool then the burner comes on.

   If ignorance is bliss why aren't more people

   happy?

3. 
   junkhound | Dec 27, 2005 09:31pm | #4

   For very low cost (as in free) have used old car air conditioner condensors in ducts (hot water from fireplace).  If you dont have a few old junkers in the back yard, you should be able to get a condensor to fit your duct at a wreching yard a lot cheaper than buying an HVAC product.

4. 
   BossHog | Dec 27, 2005 10:02pm | #5

   Seem to me that putting it in the return air duct would make your furnace less efficient.

   The colder the air is that goes into your furnace, the more efficient it is at pulling heat out of the heat exchanger. Warm up the incoming air, and it won't pull as much heat out of the furnace.

   I wonder if it would be better to run the warm water through tubing under the floor, providing some radiant heat.

   Old age comes at a bad time
1. 
   DanH | Dec 27, 2005 10:10pm | #6

   It's a tradeoff, of course. You'll lose efficiency but if the hot water is "free" you're still ahead. You can compensate by increasing fan speed, but then that complicates the control system (since you'd prefer to run low speed on hot water only).
   If ignorance is bliss why aren't more people

   happy?