Hot water circulator question.

Discussion in 'HVAC Heating & Cooling' started by shendog, Jan 6, 2010.

  1. shendog

    shendog New Member

    Messages:
    4
    Location:
    PA
    Hello everyone!

    I have just recently purcahsed a home (my first home). The home has oil hot water and heat; and a wood/coal stove backup. The wood stove is already plumbed into the house hot water system, but has no circulator of it own. The wood stove does have a controller for a circulator, and a wire has been run over to the circulator on the oil furnace; but not connected. My question is this: Can the oil furnace controller, and wood stove controller both be connected to the circulator pump simultaneously? My understanding is that these controllers are esentially relay switches, and there is no danger of back feed. However I want to be sure, before I connect it up that way. Don't want to let the magic smoke out of anything expensive!

    As always, I would greatly appreciate any help you can offer!

    Shen
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,128
    Location:
    New England
    Yes, there are potential problems with doing this directly. Yes, if done properly, you can have two items control a single circulator. The safest way to do this is probably with an additional controller. It would take the inputs from the existing devices, and control the circulator. If both relays were on the same leg of the power, it might work. If someone moved a breaker, you'd mess things up the first time it came on. www.tacohvac.com among others, make controllers designed for combining things like this.
  3. shendog

    shendog New Member

    Messages:
    4
    Location:
    PA
    Thanks for the response jadnashua. Both the stove and furnace controls are feed from an auxiliary fuse panel; so they are on the same circuit. last night I shut off the power to both and checked the resistance of the furnace, and stove circulator outputs. Both show open circuits (millions of ohms). This would seem to indicate that there is no possibility of back feed to either controller.

    A friend who works in the industry is going to stop by and look at it tonight. I'll let you know what we come up with. I'll also check out the controllers jadnashua mentioned.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,128
    Location:
    New England
    Power to the circulator probably comes from a relay. But, it may not be a mechanical relay, it could be electronic. If it is mechanical, and you are certain you are on the same phase, two different relays applying power to the same circulator isn't a problem other than a safey issue (i.e, service one device with the power off, and it is applied by the other can get really exciting!). If either one is electronic, then you'll probably blow something up. If the panel is fed by 220, then yes, even on 110, you could be on opposite phases on the two devices. This would be the more common way to do this, so be careful - you may be ending up applying 220 or blowing things up before the fuse or CB pops.
  5. shendog

    shendog New Member

    Messages:
    4
    Location:
    PA
    My HVAC buddy stopped by last night and looked it over. He didn't see any issue with with running the circ pump off of both controllers, so I went ahead and connected it up that way. So far so good. I built up a good fire last night, and adjusted the stove controller. When the stove temp. reaches 180F the the circulator turns on. This morning I turned the temperature up on the oil furnace and this activated the circulator as well.

    I looked the wiring over pretty carefully last night before wiring this up. The stove, and furnace are both powered from aux fuse panel, that is feed from a 120 breaker in the main panel. Each is on a separate fuse in the aux box. Shouldn't really be a safety issue to anyone working on it. If the Breaker or aux box are switched off, both units are dead.
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