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Smith boiler question

sw18x Member Posts: 19
Simple question:

 Can I adjust the temperature at which my gas boiler kicks on? I'd like to lower it from where it currently is (presumably around 185 because I have baseboard heat) to around 170. I can't find any obvious control for this on my boiler.

Complicated explanation:

I just bought a house last March with a Smith GB100 gas boiler. I'm not sure how old it is, though it looks to be fairly new. The house also has an outdoor wood fired boiler that heats a garage with radiant floor heat and "supplements" the indoor heat: pex tubing from the wood burner runs into the "hot water tank" (not sure if that's the correct terminology here) located next to the boiler in the basement. The wood furnace also supplements a separate hot water tank for domestic hot water, but that is in a completely different loop.

The former homeowners told us that they kept the outdoor wood furnace water temp around 130 degrees. Talking to other people with outdoor wood "boilers", that seems low - I'm told that a 160 to 180 range is more common. Not only that, but a buddy of mine told me that baseboard heat is usually set around 180 to 185 degrees. If that's the case, then unless I keep the outdoor wood furnace hotter than the lowest temperature the water in the indoor boiler naturally hits between cycles, won't the wood burner actually pull heat from the gas boiler and cost me higher gas bills? The way I see it, without the wood burner in the loop, the indoor boiler will kick on to heat the house, then between cycles the temperature in the tank might fall to "x" degrees. When the thermostat in the house kicks the indoor boiler back on, it only has to heat the water back up to 185 from "x" degrees and maintain it there during the cycle until the house heats back up. But with the wood burner in the loop, that 185 degree water is flowing back outside into a furnace that's set for a lower temperature, and so the wood burner actually becomes a heat sink, doesn't it?

My goal is to keep the indoor gas from coming on as little as possible when I'm burning wood, so given the above, what I'd like to do is keep the wood burner around 170 degrees, and drop the temperature that the gas boiler kicks on to about the same. I read in the online literature that the current Smith G series kicks on the gas burners when the temp. falls 15 degrees below the cut out point for the burners. But can I adjust this setting on the gas boiler? I see no control that would allow me to adjust this.

Any help or advice here would be greatly appreciated. None of the heating companies around here want anything to do with servicing the outdoor boiler, and they don't seem to have any experience with this kind of set up. I do have a company coming out on Nov. 10 for standard maintenance of the gas boiler, but I'll be firing up the wood boiler this weekend, as the temperature here is expected to fall into the 30s. Thanks for your help.


  • lchmb
    lchmb Member Posts: 2,997

    seeing your setup in person, its hard to say. But I  have a couple family member's who run wood boiler's. They run their wood boiler at 180 degree's and shut the gas off completely. The only time the gas come's on is if they leave home. With that said, you could set your boiler aquastat at 150 that way if your wood system starts to cool, you have some heat from the boiler. But generally once the wood is fired up, it run's a day or two before needing more..They have their circulators wired seperate from the boiler btw, that's how they can shut it down...
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    I have a feeling the outdoor

    wood boiler was strictly for the radiant floor and maybe domestic hot water. The radiant floor can't go above 120 to 130 so if you are going to run it at 180 or 190 you will have big problems with the radiant floor at it can't run at that high a temperature.

    Show some pictures of the gas boiler with the cover off as that is what will show the high limit or any other limits which can be adjusted for temperature.
  • kcopp
    kcopp Member Posts: 4,189
    Pull off...

    the front cover. On the inside there will be a small box labeled honeywell. Pull that cover off. the dial has numbers/ temperatures stamped on it.
  • sw18x
    sw18x Member Posts: 19
    Mixing valve?

    Thanks Tim.

    I finally got hold of a guy I know who's in the heating business. He said the same thing - 180 degrees is too hot and will ruin the concrete. He mentioned a "mixing valve" that might allow me to run water to the concrete at one temp, water in to the house at another. Like I mentioned, the frustrating thing is, there's nobody in the area who services these outdoor boilers, and I don't have the experience to install something like that myself. I'm hoping he'll be able to help out - do you have any experience with mixing valves? Is it a quick install? What else does it involve other than simple plumbing? I'm assuming another thermostat would have to tie in to keep the water at a specific temperature?
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Mixing valves

    work with water temperature sensors. There are control systems such as Tekmar that can sophisticate your setup and do what you want. Perhaps your friend can hook that up for you.
  • sw18x
    sw18x Member Posts: 19
    edited October 2011
    Turns out...

    Turns out, upon closer examination, the hot water from the outdoor wood burner runs into a single wall "heat exchanger" in the tank pictured above, and does virtually nothing to heat the water on the way to the gas boiler anyways. I watched a full cycle of the Smith boiler with the outdoor pump turned off, then turned the outdoor pump on and let it pump 150 degree water through the exchanger for at least a couple hours before watching another cycle of the gas boiler. In both cases, when the thermostat kicked on the result was the same. The water temp had fallen to 130 degrees, and it took equally long to climb back up to where it peaked around 210. I've got a diagram from the manufacturer showing how to plumb the outdoor boiler directly into an existing indoor boiler, but unfortunately I'm still having trouble convincing somebody around here to take my money. I live in the Rochester, NY area by the way - if anyone knows someone nearby who could tackle this, please let me know. Thanks.
  • lchmb
    lchmb Member Posts: 2,997
    wood boiler

    You do want to keep the plate exchanger for the wood boiler. Just allow the wood boiler to run to 180 degree's and allow the boiler to take the heat from the plate exchanger with the system circs (or add a circulator to pull the water into the boiler) ...I have seen the wood boiler piped directly through a boiler and having an open system with a lot of make up water can cause problems. If the plate exchanger is not transfering a lot of heat it could be plugged.
  • sw18x
    sw18x Member Posts: 19

    I've got a heating guy coming out next week. Thanks for the input, I'll steer clear of plumbing the water directly into the boiler from the wood burner, although I wish there was a better way to make good use of the wood burner to heat the house. The installation guide that came with the outdoor burner does have a diagram showing how to tie into the gas boiler - what kind of problems can this lead to?
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,253
    What kind of problems you ask?

    The excess oxygen in the open system from the wood boiler can rot out your gas boiler in a year or two. The dissolved gases can come out of solution and cause air binding of your heat pipes. The low water temps can in some cases cause condensation to for in the flue passages of the gas boiler leading to more rot.
    Cost is what you spend , value is what you get.

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