# Wood burner with propane forced air furnace



## open68 (Nov 12, 2012)

First and foremost please bear with me and if I miss anything just ask as this is my first time dealing with this type of idea and the rational of thinking.

Ok here goes::banana:

First I live in the thumb of MI. Ok g/f has a forced air propane system for the main part of the house and in the basement (livable space) there is radiant in floor heat from a out side boiler wood burner. Said wood burner also has a unit in the forced air system. 

Ok with the basic set up out of the way here is my question. To run the forced air system she just turns the blower from auto to on leaving the heat/cool selector to off so the burner will not kick on and waste propane. But by doing so it gets left on to long and wastes elec. So what my line of thinking is there any way that it can be turned on the heat cycle and avoid the burners coming on just cycling the blower when heat is called for?

I thought of just cutting off the pilot by shutting off the propane but once the thermo-couple sensed no flame would the system cut out? Or if it is a elec igniter would the igniter keep clicking on on a call for heat? I am trying to figure a way to run the forced air system with out the propane and not on the on setting but auto to save money.

I hope that this is clear enough to get the jest of what I am saying. No I do not know the make and model of the furnace or wood boiler. Any questions on information that I may have omitted please ask as I know there has to be an easy solution to this problem.

Thank you in advance
Steve


----------



## Kevingr (Mar 10, 2006)

Couldn't you add another thermostat that is set higher than the propane thermostat and run those wires to just control the blower and not the burner on the forced air unit? Seems like that would work, but I wouldn't know how to wire it.


----------



## open68 (Nov 12, 2012)

Kevingr said:


> Couldn't you add another thermostat that is set higher than the propane thermostat and run those wires to just control the blower and not the burner on the forced air unit? Seems like that would work, but I wouldn't know how to wire it.


I was thinking this option also and am thinking that I would just not hook up the wire to ingage the regulator? I am not a 100% sure on how to wire it either since I have not touched havac units in over 20 yrs LOL 
Steve


----------



## Gianni (Dec 9, 2009)

The main costs in running a motor are the starting windings. I was told many years ago that it was as expensive to run a motor for 3 hours as it was to start it. I would calculate the amperage used and find out how expensive it really is. To wire in the blower on a thermostat you would need to come off the existing wires from terminals R & Y [should be a yellow and red wire if done correctly] and run them to a thermostat. When the temperature dropped to 70 the circuit would make and the fan would run. I would get a cheap thermostat and eliminate the heat anticipator if I wanted to do this. The disadvantage may be a that it cycles on and off frequently because of the cut in and cut out temperatures built into a thermostat. You might be able to attach it to a relay when the wood burner circulates fluid but that might require elimintaing it from the furnace circuit. 
In the 70"s the shop I worked at would set up fans to run full time. They sold a device that varied the fan motor speed to high when the heat exchanger was hot and slow when it was cold. They only worked with a belt type fan and when most furnaces went to direct drive they became obsolete. The principle still works and is in use in some high end furnaces.


----------



## artificer (Feb 26, 2007)

If the forced air furnace is at all newer (20yrs?) then it should have a thermostat control for just the fan. Take a look at this site, or google furnace thermostats.

Wire a second thermostat to the cooling connections. When it gets cold, the furnace fan kicks on, and circulates air. Set it a couple of degrees warmer than the main thermostat. If the wood burner can't keep up with the heat, the propane burner starts up. Choose temperature difference that makes sense, or try it out. I'd start at 5 deg F difference.

How is the heat controlled in the wood burner? By you stoking it, or does it have a thermostat? If it has its own thermostat, you could use that as well. You could also use a thermostat that checks the temperature of the incoming water: if its hot, then it turns on the furnace blower. When the pump stops, the water cools, and the furnace stops. Alternatively, you can wire up a control relay parallel to the water circulation pump. When the pump is on, the relay activates, and tells the furnace that you want cooling/fan only. Personally, this is the way I'd go unless you have a large water holding tank in the wood burner system.

As for the power used to start a fan...
An AC motor starting draws up to 5X the amps compared to running. This should only last 5 seconds or less. If you use these numbers, then you use 25X the power starting as you do running, or 1 start = 25 seconds of run time. No where near 3 hours, unless the motor is unloaded, which it won't be. Its better to start/stop the motor every 5 minutes, rather than leave it on continuously. Start time should be 1-2 seconds, typically, so even less power is used.

Michael


----------



## open68 (Nov 12, 2012)

Cool I like that site. I will see what I can find and go from there....


----------

