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I have an outdoor wood burner with a water jacket. It has an electric blower that needs to run to get the fire going hot enough to be clean burning. I have a 200 gallon storage tank, and plan to enlarge it to 1000 gallons. I pump water out of the tank to the wood burner, then the hotter water goes to the house and through an exchanger in my furnace. Then the cooled water goes back to the tank.

Is there a thermostat that will kick just the furnace blower on at say 68 and turn it off at 71 but still let the furnace light and work normally at a lower temp like 50?

  • You clearly have two separate issues here. Let's deal with one at a time. The furnace first. I need make and model off the furnace or can you tell me if the furnace has an integrated furnace controller. An integrated furnace controller, IFC is a fairly large, 6" x 6" PC board normally located in front of the main blower assembly. If the furnace is fairly new it should have an IFC. On the Ifc – Paul Logan Nov 15 '17 at 22:39
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    You need a 2-stage thermostat. The fan circuit would be switched on when either stage is running. Connect only the second stage to the furnace so that it kicks on when it gets to that lower temp. – Jon Nov 15 '17 at 22:41
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    @Jonathan You should add that as an answer. Using a 2-stage thermostat is likely a good solution. – Tester101 Nov 16 '17 at 15:04
  • I've edited the post to make it a single question. If you have more question, please ask them in a different post. – Tester101 Nov 16 '17 at 15:05
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To accomplish this, you can use a 2-stage thermostat. You'd connect only the 2nd stage to your furnace. Both stages run the blower.

When the temperature drops to say 69, the first stage will start your blower. When the temperature drops to an even lower temperature, the furnace (stage 2) will be switched on just as you describe.

There are many thermostats which can accomplish this. Here's a great video I found which demonstrates how a 2 stage thermostat works. You can see that the first stage is activated when the temperature is slightly lower than the set temperature and the second stage is activated when the room temperature is much lower than the set temperature. There are dials to set when the second stage is activated. He also shows the wiring for the stages. In your application, you'd leave w₁ unconnected and connect your furnace to w₂.

How 2 stage thermostat

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You clearly have two separate issues here. Let's deal with one at a time. The furnace first. I need make and model off the furnace or can you tell me if the furnace has an integrated furnace controller. An integrated furnace controller, IFC is a fairly large, 6" x 6" PC board normally located in front of the main blower assembly. If the furnace is fairly new it should have an IFC. On the IFC, if you apply 24-volts, taken from the red terminal, to he green or G terminal (where all other thermostat wires are connected) the fan will start and run, normally on high speed, and continue to run as long as the IFC sees 24-volts on the G terminal. This should not interfere with the other normal operations of the furnace and thermostat.

The next control element to tackle is when to start this independent fan operation. I would recommend to start it whenever hot water is being deliver from the remote source. You will need something like this White Rogers #1609-101 remote bulb controlled switch. They are available from a number of online suppliers; SupplyHouse.com is one. Tape the bulb from this switch to the pipe delivering incoming hot water. Then insulate over it well. This controller switch will close as the temperature the bulb is sensing rises. Set it to turn on at about 120* and off at about 95*. Take a control wire from the R terminal on the IFC run it through this remote activated switch and back to the G terminal. This will control the fan of your furnace based upon the temperature of the water flowing to the exchanger. The standard operation of the furnace based upon the signal sent from the wall thermostat should not be affected. Let me know if you are still with me and if this makes sense. P.

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