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programmable thermostats

Post in 'DIY and General non-hearth advice' started by freebird77, Sep 6, 2007.

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  1. Mo Heat

    Mo Heat Mod Emeritus

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    My can do auto with fan on continuous or fan on for 20 minutes each hour (called Circulate mode). It's a Honeywell TH8000. Runs around $100 on the web.

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  2. cgeiger

    cgeiger New Member

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    Thanks, Mo Heat. I took a look at that one as well. Can you clarify the behavior of the "continuous" part. Do you mean that when the T-stat sense the usual 2 degree dip below setpoint, it only kicks on the blower not the compressor and blower? Or, do you mean you can just set it blow continuously without the compressor until you turn it off again. I liked the 20 minutes circulation each hour - though. Seems like that might be enough of a compliment to the fans I have trying to push air in/out of the stove room...
  3. Mo Heat

    Mo Heat Mod Emeritus

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    Well, this thermostat is a little different than any I've had before. It has no "Swing" adjustment. I was ultra concerned about this when I got it, but it's been no problem at all in the year or two I've had it. I was certain it would be, too. Anyway, that's the long way of saying that with my T-stat there is no 2 degree dip for a demand. It's much more like half a degree, or three quarters, or just off the degree setting it's on... not sure which. Never figured that out.

    So... it doesn't do much of anything different with the fan than other thermostats. But it does have that CIRCULATE feature that turns on the fan for 10 minutes, off for 20 minutes, on for 10 minutes, off for 20 minutes, repeat...

    When there is a demand for heat or A/C, the fan can't come on by itself without the heat or A/C. The heat or A/C always comes on when the temperature rises or falls above or below the demand setting. If the FAN is set to AUTO, it comes on at this time, too.

    The FAN setting is a touch control with three settings, (ON, AUTO, CIRC):

    When you set the fan to ON, it's ON, all the time (demand or no demand).
    When you set the fan to CIRC, it's on 10 min, off 20, repeat.
    When you set the fan to AUTO, it comes on with a demand for heat or A/C.
  4. cgeiger

    cgeiger New Member

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    Thanks for the description, Mo Heat - that about seals it for me. The circulation feature sounds perfect! I had envisioned it running off for 40 and on for 20 as opposed to on 10 off 20, repeat. That should fit my situation closely enough to do what I had envisioned.
  5. Gooserider

    Gooserider Mod Emeritus

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    Another option is one that shows up in the banner adds every once in a while, it's a little box from "Bear Mountain Designs" that splices in parallel with the regular thermostat and cycles the fan only automatically. It can be programmed for a fairly wide range of on-off time ratios, and allows the regular thermostat to do it's thing without interfering.

    We had one for a while, and while it worked sort of as advertised, we weren't happy with it, and I ended up selling it to someone else...

    Problems -

    1. For some reason, in addition to the fan, the unit also made the Central AC compressor kick on - Bear Mountain said this was a known bug with some electronic thermostats, and that the easiest fix was simply to pull the breaker on the AC unit...

    2. It may or may not be related, but a few months after we put the unit in, the blower motor on our relatively new HVAC unit had a bearing failure and started screeching on startup. (Blower replaced under warranty for a fairly expensive service fee.)

    Installation and operation were not a major problem, but the net result was that the house did not appear to get warmer... The temperature in the living room (where the stove is) dropped, but the rest of the house didn't seem to get any warmer. What we ended up with was a personal confirmation of the general experience of most posters here, namely that the HVAC system does a lousy job of moving stove heat... It appears that the HVAC loses more heat going through the ducts than it picks up from the stove.

    I'm mentioning this as an option, personally I'm kind of neutral on reccomending it - it did what it said it would, but what it did wasn't very satisfactory for us, but YMMV.

    Gooserider
  6. cgeiger

    cgeiger New Member

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    Interesting feedback, Gooserider. I have to admit that running the fan only even manually doesn't seem to work too well to move the heat unless we've reached a certain exterior temperature to begin with (i.e. 40s). One thought is that my basement ducting is uninsulated (I'm guessing that's pretty common). So the warm air has to pass through cold ducts to get to the registers on the first floor. Being that the ducts are aluminum and reasonably conductive they should act as mini-heatsinks. I'll have to try some more experiments after we've passed the arctic phase here and get back to more seasonal temps for the mid-atlantic. If I can get anything repeatable, I'll be sure to post the results.
  7. Gooserider

    Gooserider Mod Emeritus

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    Our basement ducting is also uninsulated, though the basement is nominally in the house heating envelope. It probably helps us in the summer with the AC, as the basement stays pretty cold, but in the winter I'm sure it doesn't do much for the heating... I think more to the point is that the air in most stove rooms is not any where near as warm as the heat exchanger in an HVAC unit, so the volume of air that gets moved isn't really enough to make a lot of difference.

    Whatever the cause, we if you search back through the threads, you will see that attempts to move stove heat around with the HVAC system is a chronically appearing theme, with VERY few, if any people reporting that it is successful...

    What seems to work the best is to carefully plot out the natural air flows in the house, often using an incense stick or cigarette to check flow direction at both the top and bottom of each door way, and try to use fans to increase those flows - preferably by moving cold air towards the stove, as opposed to trying to push hot air away from it.

    Gooserider
  8. kbjelka

    kbjelka New Member

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  9. kbjelka

    kbjelka New Member

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    After looking over the Lux site it appears most of their programmable models have a keyboard lockout feature. I have been really happy using the TX9000TS with a Quadra-Fire Castile. Picked it up on eBay as an open box special. Good luck!
  10. Redox

    Redox Minister of Fire

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    Bear Mountain should realize how the typical CAC thermostat is wired: If the thermostat has a mechanical switch for AUTO/ON, the switch connects Y and G together in the auto position to bring on the fan and the compressor together. Most electronic thermostats have separate relays for Y and G and won't do this if the "switch" is electronic. It would be better if they used a SPDT relay with the common contact connected to the fan relay (G wire), NC to the G terminal of the stat, and the NO relay to the R wire or terminal. The idea is that when activated, the timer breaks the G connection from the thermostat and connects it directly to the R wire. This will keep the compressor from running unless the thermostat is actually calling for cooling.

    Chris
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