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help with wiring wood boiler thermostat to run gas furnace forced air blower

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by rallen12, Dec 15, 2012.

  1. rallen12

    rallen12 Member

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    I have an eko 40 with 500gal. tank. I have that loop controlled by eko control and primary pump. I have a secondary loop from the tank to the forced air gas furnace in the house. This is powered by a circulating pump and will be controlled by a thermastat in the house. I am presently trying to set up the thermostat so it runs the gas furnace blower (first mistake- learned how to turn the air conditioner while heating by wiring the gas furnace thermostat to the wood boiler thermostat).

    The gas furnace blower has a honeywell mini zone controller. I know I cant wire 2 honeywell thermostat to accomplish, but can I wire the would boiler thermostat into the mini zone controller (ie setting the gas furnace thermostat lower as back up for wood boiler) or do I have to wire the wood boiler thermostat directly to the blower with relay switch.......I am hoping all I have to do is parallel wire thermostats to the mini zone controller and set the thermastat accordingly (gas back up, wood primary).

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  2. goosegunner

    goosegunner Minister of Fire

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    I don't have the schematic with me right now but my forced air coil systems uses one thermostat. It does not use the ac side at all. I have an aqustat right at the coil. It is wired to a time delay and two Rib relays.

    On a call for heat fan comes on, pump starts. If the water is not 130 degrees at the coil after 3 minutes the pump stops and the gas furnace fires. The only way to tell the difference in which is running is to

    1. Visually see the exhaust from propane furnace.

    2. Be near furnace and see red lights on the Relays one labeled gas or wood

    3. Hear the pump stop in the garage and furnace still running

    I like the set up very much. It is seem less and there is no extra thermostat or differential setting between wood and gas.

    gg
  3. rallen12

    rallen12 Member

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    I have a conceptual idea of what you are saying but when I look at the blower and see 10 thousand wires going to the blower and to the mini zone controller from a circ. board (in furnace) I am lost. Thought there may be a way to wire the thermostat without getting into the rats nest of wires in the furnace blower.... Did try wiring the thermostat (home wood boiler) to the mini zone controller..fan did kick in but so did the AC (same result)... again. Not sure why the AC comes on when the gas furnace thermostat is on heat set at 65 and the wood boiler thermostat is set to heat and 72. At any rate it I did a drawing...any other ideas???

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  4. brant2000

    brant2000 Burning Hunk

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    I use my heat pump blower connected to a second (two wire, heat-only) thermostat. That gives me the ability to set the blower to kick on a few degrees before the heat pump would start. I just connected that second thermostat in parallel with the blower relay (I believe it's the green wire on my unit). It really is a very simple setup, but it works. The circulator sending water to the furnace coil is always on, which actually works pretty well because it seems to put off a small amount of heat all the time even without the blower running.
  5. stee6043

    stee6043 Minister of Fire

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    I use the AC circuit to run the boiler side pump and furnace fan. I simply throw the breaker for the AC when heating season comes along. It thinks it's running the AC but only the fan comes on, not the compressor. I think it's hard to beat using the AC wiring when it comes to simplicity.
  6. rallen12

    rallen12 Member

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    "now were cooking with peanut oil" I am always in aw of the genius of simplicity.... thanks for the tip.
  7. stee6043

    stee6043 Minister of Fire

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    This should go without saying....but I failed to mention I have a second thermostat that I wired to the existing thermostat on the AC side of the circuit. Obviously, you need a call for heat from the new thermostat but it's calling over the AC side of the circuit. Presto...a total of 6" of wire needed on the thermostat side.
  8. Tennman

    Tennman Minister of Fire

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    I try to read these discussions so I can better understand control and I swear my brain just goes into reboot. I need to be more mentally disciplined.... but I hope you didn't create the problem I have. I absolutely should have run some of that CAT wire with my underground so I could send control power to my boiler barn. For me at the moment I'm blowing money because my circ pump, out in the boiler barn, runs all the time except when turned off by my boiler controller due to low boiler temp limit. This is so rarely talked about I guess because it's so painfully obvious..... except for the "control disadvantaged". I believe virtually everyone here kills their demand circ pump until the blower in the house is commanded to come on. Course if your boiler is in the house it's no big deal to correct.... but if it's 140ft away from the blower (like yours truly)... well... it looks like it'll involve dirt work (for the THIRD time). Ya'll correct me about this but I think most here don't let their demand pump run continuously. Please feel free to confirm this. I've actually considered looking into a wireless solution to avoid dirtwork yet again!! :confused:
  9. goosegunner

    goosegunner Minister of Fire

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    My boiler pump is independent of my load pumps. Once my storage is up to temp and the boiler pump is off my primary secondary setup in the attached garage is set up to be on demand with a Taco Zone controller. The pumps only run when there is a call for heat. The on demand helps a lot with my forced air coil so I don't continuously mix the tank. My next addition will be a buffer tank in the basement to keep hot water close to the coil at all times to reduce the delay.

    gg
  10. goosegunner

    goosegunner Minister of Fire

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    Why not install or move your load pump for demand to the house? No dirt work then. I think you can buy a 2 zone Taco controller for about $50.

    gg
  11. Tennman

    Tennman Minister of Fire

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    rallen, no attempt to hijack your thread, just trying to prevent you from repeating my mistakes.

    GG, Someone else suggested to me to move my pump, but my 0013 Taco is pretty noisy. That may be because I placed my expansion tank in the root cellar far away from the pump. I've since learned it's best to place the expansion tank directly "upstream" of the pump to reduce cavitation noise. Moving the pump would place that noise maker directly under our TV/entertainment room. Presently I can hear the 0013 humming from 50' outside my boiler barn so it would definitely be heard in the room above.

    So it appears that virtually everyone has their HX (demand) pump off until the fan comes on. It wasn't until my 3rd year of operation that I became aware that was SOP. A buffer tank in our root cellar will definitely be added along with the storage upgrade to reduce the delay of getting hot water to the HX on fan startup, that's a great idea. Is a 2 zone controller like a relay that turns on the Taco? If I rent one of those machines that just slices the ground to place a wire without digging a trench and I run a CAT wire to the barn, then I guess I'd place that 2 zone controller in the barn and the controller would supply power to the 0013 by the same thermostat signal that turns on the fan? BTW, with other business and personal projects behind me, I intend to purchase Laddomat to manage flow between the boiler and storage when storage gets added at the end of this burn season. I'll need to keep the 0013 because of the flow and head loss calcs for the demand loop. Running that CAT wire appears to be the simplest way for me to reduce electricity of that 0013 AND prevent that flow from stealing stored energy in the tank. Thanks for helping me talk thru this control stuff and maybe rallen will learn something also.
  12. goosegunner

    goosegunner Minister of Fire

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    You will need underground rated wire, plus the rental. It would most likely be cheaper to have the controller and pump in your house or garage.

    Mine is in the garage. I have a primary/secondary manifold with circulators that are controlled by a Taco 4 zone panel. I have it in the garage because one zone goes out to my pool heater in the summer, keeps heat out of the house in the summer.

    gg
  13. heaterman

    heaterman Minister of Fire

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    We use the Fan terminal (G) on the furnace control board to energize the fan only on a call for heat, using a second thermostat. You can as others have said simply throw the breaker on the A/C to keep it from running but it will still be pulling in the A/C contactor on the outdoor unit.
    If you want to get fancy, get a 4 pole double throw switch from radio shack or an electrical supply house and wire it up so the normal thermostat goes to one pole and the two wire from your wood thermostat goes to the other side. You'll wire the furnace R,W,Y G terminals to the center of the 4P2T switch. The normal T-stat will wire correspondingly to the R,W,Y,G terminals and the wood heating stat will wire to R/G. Simply throw the switch one way or the other to change from wood to regular fuel. In your case, you would wire from the zone control to the normal side of the switch.
  14. Tennman

    Tennman Minister of Fire

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    Thanks guys. I'm inclined to just run the wire underground because of the concern of the pump noise in my home. I think I've got it on the thermostat HM or at least I can have my HVAC guy read this! And it looks like I can then put the controller for the 0013 in the barn.

    HM, you think moving my expansion tank to the boiler barn just upstream of the 0013 will quiet it down? I followed another thread about where to place expansion tanks and I think that's what was concluded.

    Thanks
  15. heaterman

    heaterman Minister of Fire

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    Nearly all of the systems I see around here have the main circ running 24/7 circulating water from the wood boiler location (wherever that is) to the house. This is speaking of boilers located away from the heating load........ The issue with starting the circulation with the call for heat is that if it has been off for some time, you have to move a shot of cold water through your heat exchanger before getting any output from it. On a typical fan forced/hot water coild system, this means incorporating some type of delay on the fan to avoid getting cold air from the registers until the coil heat up.

    Without knowing all the details of your system Tennman, I have to say that a 0013 is going to be noisy compared to say a 0010 or other lower head pump regardless of location. Do you need that much pump?
  16. dogwood

    dogwood Minister of Fire

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    Interesting thread. Heaterman, what does "pulling in the AC contactor" mean? Is that something on the outside AC unit that shouldn'y be turned on?

    Mike
  17. hartkem

    hartkem Member

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    The outside part of your AC system(condensor/fan) has a contactor or relay. It allows low voltage (24) volts to control the fan and compressor. it really shouldn't hurt much of anything i wouldn't think. if your not familar with a relay google it and you will understand what I mean.
  18. taxidermist

    taxidermist Minister of Fire

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    HM he needs that much pump just like I do. I went with the taco 10 this year and it will not move enough water to keep the boiler from overheating.
  19. heaterman

    heaterman Minister of Fire

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    Even if you throw the breaker for the outdoor unit the 24V signal from the furnace will still energize the contactor coil on the 24/240V relay out there. So every time the furnace fan runs that contactor will cycle. Just extra wear and tear.
  20. stee6043

    stee6043 Minister of Fire

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    What I found most interesting is that my furnace already had a delay function built in for the air conditioning. In the summer my AC compressor starts before the furnace fan turns on. Maybe 30 seconds? So as I use the AC circuit to run the fan for my boiler I get the same delay. Works perfectly as you've stated above. Although I have less than 15 feet of pex between my storage tanks and furnace so really my "cold slug" issue would be negligible even if I didn't have a delay.
  21. BravoWhiskey

    BravoWhiskey New Member

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    Motor contactors typically are speced to handle a million or so mechanical cycles or a hundred thousand cycles under load, so probably no concern for wear and tear in this case.
  22. Tennman

    Tennman Minister of Fire

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    HM, Yeah per the Taco TD010 my system is right on the edge of the to provide the necessary gpm with the 1 1/4" line to deliver ~80% btu capacity of our boiler. A computed head loss of ~27' which is based on the distance (nearly 400' round trip), ells, tees, HX, etc requires the horsepower of the 0013. Had I not been cheap, 1 1/2" pex would have reduced the gpm considerably and I might have gotten by with a less horsepower pump (lower velocity) and long term electricity savings. Woulda, coulda, shoulda.... But.... other than the noise.... I'm good. Never being around another 0013 so I have no point of reference of how noisy they typically are. So I'm paying an electricity price for putting my boiler so far from the house, but I'm good with that also. Winter for me is nothing like winter for ya'll up north. Still our propane savings are in the thousands of dollars burning wood in our BioMass so some added electricity cost is not a big deal. Besides I now really enjoy the whole wood burning thing.

    So this topic of starting/stopping the demand circuit is rarely discussed regarding those of us with LONG slugs of water. And whether starting/stopping makes sense from a total energy required perspective. I know it takes a lot of energy (electricity) to get that whole slug of water going again after it stops. I guess it depends on how often the fan kicks on whether stopping that long train of water makes sense. I discussed this with Taxi last year and I know he stops his pump, but I'm certain his home is more efficient than mine (reflected in fan duty cycle). It's actually good to hear there are folks who keep the flow going all the time. I presume these are Garn folks. I'll try to do some energy calcs based on simple momentum assumptions. Could be the physics says keep it moving. I'll keep ya'll posted. Regardless good to know some folks CHOOSE to keep it moving all the time!

    Rob, I'd be glad to fill out my TD010 spreadsheet with your system and do flow and head loss calcs for your system. Wouldn't hurt to know where you stand.

    Sorry, rallen to get so far afield of your thread, but welcome to the University of Hearth, we do rabbit trails often.

    Thanks ya'll
  23. Fred61

    Fred61 Minister of Fire

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    I don't know much about how the AC systems are controlled but my simple mind tells me to launch the circulator with the room thermostat and launch the furnace fan with a snap switch of whatever value it needs to be attached to the coil. Should be able to intigrate it with the furnace control. May need a diode or two in there to prevent backflow.
  24. dogwood

    dogwood Minister of Fire

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    Fred, that's exactly the way I'm wiring mine. I'm too ignorant of hydronics to figure out why that wouldn't work.

    Mike
  25. Downeast Farmer

    Downeast Farmer New Member

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    When using a heat exchanger plumbed from some sort of boiler that is placed in the plenum of the forced air furnace, does the water in the heat exchanger always circulate? Is the heat demand satisfied only by the forced air fan coming on, rather than some sort of circulator coming on to move water into the heat exchanger? Seems watt-wasteful. What's the most efficient way to run this heat exchanger (while taking the couple of years to switch to radiant....)?

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