Install question for you all

[cumminstinkerer]

I recently helped a fella install a Polar G3, everything went very smoothly until it came to making LP furnace fan to work. The furnace is a 98% Lennox with digital control and fan. I installed a second thermostat to control the switch the fan on and off when running with the wood side, and still allowing propane to function for back-up. Well the dilemma comes in that you cannot just bridge the red and green wires ( red being power and green is fan control wire) on the older systems you could literally jump those wires from the LP thermostat to the wood thermostat and control the wood heat, not so much with this LP furnace. It will not turn the fan on setup that way, my friend is getting by with simply turning the fan on and off manually with the LP thermostat but this sure isn't ideal, does anyone out there have any insight on how to make this work? and I also want to share so that anyone else doing an install knows this can be an issue, according to the HVAC pro my friend is dealing with hooking things up like this can damage the circuit board (thankfully that did not happen) but I would sure hate for someone to make the same mistake and fry a board.

Thank you

 

[sloeffle]

Is it a heat pump, or is there a Y1 terminal on his existing thermostat ? If it is, I’m in the same boat and have a solution. 😃

Your HVAC buddy is right, you definitely don’t want to mix 120V and 24V, bad things will happen.

 

[cumminstinkerer]

It is a propane furnace, I am not sure about a Y1 terminal, I am hoping to leave him with a thermostat to control the wood side and one for the propane, that way he can set wood for comfort and propane as backup.

 

[sloeffle]

You can do it with just one thermostat. It's a much better setup IMHO.

Since they aren't on a HP you'll probably need to use a meter ( 24V AC ) and determine what wire is being energized. Maybe the W wire based off of this article. Once you determine what wire is being energized you'll want to switch that wire based the water temp in the air-water HX. You can do that via a Ranco or Honeywell ( more $$$ and the directions are horrible ) temperature controller. Essentially what those are doing is keeping the circuit closed ( NC ) and then once the temp sensor hits a certain point ( 130 - 150F ) they are opening up the circuit so the fan will run at full speed but the propane ( W wire I'm assuming ) won't kick on. This should be a higher fan speed than "fan" speed on your thermostat. My furnace has four different fan speeds based off what's running and what stage.

Ranco Install ( he has some really good videos )



I like to make things hard on myself so I'm going to use a Auber PID controller and thermocouple to sense the water temperature. Very similar setup to what the guy are doing with their Tundra / Heatmax wood furnaces.