How to make furnace circulate hot air from stoker?

I have an Alaska Stoker, I would like to run a pipe into my return of my hot air furnace (already done) and be able to use the fan in the hot air furnace to circulate the air. My question is, how do I make the thermostat run the fan and not fire the gas furnace. Is it possible to have it do this and when the coal doesn't meet the demand of the thermostat the gas will fire as the backup source of heat. Is it possible or am I dreaming.

Does you current thermostat have a Fan "On" Fan "Auto" switch? If so just turn it to the Fan "On" position for a test. If it pulls the air from the stove and warms your house you can take the next step. Adding an additional relay to turn on only the furnace blower is possible. Ideally you would want it to only turn on when the stove was hot. It's not a "off the shelf product" but it can be done.

Yanche

Yanche,
Yes, my thermostat has an "on - off" switch. I already tested it, and it really pulls the heat from the stove. What I want to do is have the fan from the furnace run when the thermostat calls for heat, now if the demand isn't met by the coal stove, will the gas furnace fire to meet the demand of the thermostat. If so, what type of relay and how would it be done. Or is it possible to just wire in an additional thermostat to run the fan only. Thanks for your help.

Use caution when making changes to a gas furnace. Without seeing a print of the wiring its difficult to say. Gas furnaces have safety devices built into the systems that could be bypassed by making changes to the circuits. I'm not saying it can't be done, just be careful. I would get local help with either a furnace tech or electrician on that one.

I have a hot water baseboard system in my house, but the principles are the same. I wanted to have the circulating pumps run when the zone thermostats called for heat, but I didn't want the propane gas boiler to fire untill the house got down to a much lower minimum tollerable temperature.

So I ran a second thermostat to the gas burner. I put the second thermostat in the main part of the house. I have it set at 55*. I run the rest of the thermostats at 68*. When or if the fire burns down in the coal boiler the circulating pumps will keep running pulling the last btu's from the coal boiler's water. Eventually the propane burner kicks in to keep the house 'warm'.

I just interupted the wire to the gas valve and put the thermostat in the circuit.

As said above be carefull about negating any safety items on the gas furnace.

Safety first!!


You may want to buy a heating guy a beer and have him take a look at the wiring for you.

Greg L

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How many wires are hooked to your thermostat?
2, 3, 4+?

Some furances have separate fan controls that can be hooked up to the thermostat or another switch. That would the FAN ON/OFF on the thermostat and would have 3 or 4 wires hooked up.

If the furnance is an older one, it might just have a temp. switch in the plenum and when it reaches a certain temp. the fan/blower turns on, then off at a lower temp. Therefore, you may only have a 2-wire going to the thermostat with NO fan control.

Newers ones, have circuit boards with external controls and timers. Ours has a timer circuit (on after 30 seconds / off 1 minute after gas valve closes) but, with fan override. You can change time delays by selecting the dip switch setting on the circuit board.

either way, with a bit of wiring and a relay, you could have work with either system.

i just want to run the blower from the thermostat and skip the furnace altogether. I have a 2 wire thermostat w/o an on/off switch. anyone know how to do it. Can I just take the wire off the furnace and run it to the blower on/off switch. reason is my furnace has blown a hole in the heat exchanger and I can't afford to replace it at this time but it would be great if i could move the air more evenly and efficiently. i have a fireplace insert Thanks

Ken, can you shut off the gas or oil to the burner? If so, then the thermostats will call for heat, but since there is no gas to burn, won't the circulating fans will just keep running? Or is there is a temperature limiting switch or something similar?

If you have a hole or crack in the heat exchanger, you will be circulating heated air past the hole, some may be drawn up the furnace's vent or chimney. You might want to consider a piece of duct tape over the hole to stop the loss of heated air.

Greg L

Ed wrote:I have an Alaska Stoker, I would like to run a pipe into my return of my hot air furnace (already done) and be able to use the fan in the hot air furnace to circulate the air. My question is, how do I make the thermostat run the fan and not fire the gas furnace. Is it possible to have it do this and when the coal doesn't meet the demand of the thermostat the gas will fire as the backup source of heat. Is it possible or am I dreaming.

Ed,

I have a simple solution, I am doing exacly what you want to do. Install a Honeywell Vision Pro 8000 touchscreen thermostat for your gas furnace. It has a feature that lets you set the fan to "Off,Automatic or Recirculate". In the recirculate mode, the fan runs randomly for 5-10 minutes and the turns off for 5-10 minutes.

I ran a 6" duct from my Alaska stove into my cold air return so it has to pass through my furnace filter.

The coal stove keeps my house at 72-75 degrees, I set my gas furnace at 68 degrees in case the stove goes out. If the gas furnace kicks on the fan limit switch will over ride the recirculate feature and run the fan as it normally would.

So far the furnace has not come on at all.

I am working on an improved heat exchanger, I also bought a Digital camera so I will be able to post pictures soon(the heat exchanger will be easier than figuring out this camera)

I am heating an 75 year old Story and a half about 1500 square feet, I have added in line duct fans to improve air flow up stairs.

Hope this helps

BK

Since your thermostat has a fan/auto switch, take a look at the internal wiring of the thermostat especially in the area of the fan/auto switch. This is usually a SPST slide switch. When in the auto position the switch is open. When in the fan run position it's closed. A test would be to leave the fan/auto switch in the auto position and use a jumper wire to close the connection as if you were to slide the switch to the "fan on" position. If the blower fan comes on you know exactly how to wire the contacts of your external relay. If this is beyond your understanding get some help from a HVAC or electonics technician. It's very very elementary control wiring. It would however, be changing and using the thermostat in a way never intended by the manfacturer.

Yanche

here's a good source for reference....might help on wiring.

http://www.toad.net/~jsmeenen/wiring.html

This wiring is pretty easy to do if you are an electrician. I have a blower above my stoker, but I didn't think it was pushing the air along fast enough. Look to see if you're furnace has a fan only mode and wire directly into it. Wire them to the thermostat that the other blower is wired to. Mine is on a switch so that if I am gonna use my furnace, I switch it to furnace only. If you don't know what you are doing, consult an electrician.

Im not exactly sure whats going on here, but heres what I have. I have a forced air wood/coal furnace. I wan't getting enough heat from it, so I ducted in in series with my gas furnace. I have a honeywell Control/limit on the back of my wood furnace. When the wood furnace hits 140 degrees, the blower from the LP furnace kicks on, just the blower nothing else. On my setup there were 2 wires that went from the control to the control board on the main furnace, which were R and G. This way the LP furnace uses the Wood/Furnace as a heat exchanger only and puts the heat through the home. If the woodfurnace goes out and the house drops in temps, then the LP furnace kicks in and heats the house. Because of that limit, I dont need a thermostat for that part of the wood furnace. The woodfurnace does have a thermostat upstairs beside the LP thermostat, but that runs the forced draft if I need it, which in return kicks the control in and kicks in the LP blower and heats the home.