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  1. #1
    Join Date
    Nov 2010
    Location
    Portland, OR
    Posts
    14

    Best Thermostat for Tempstar VS-95 Furnace

    I am seriously considering a TempStar VS-95 (variable speed fan, 95% efficiency) to replace my 20 year old Carrier, and to qualify for federal and state tax credits. Can I keep my programmable one stage thermostat or should I get a new one? If so, which would be a good fit? The people I am talking to seem to think that using my current thermostat would be fine (thus yielding a time based decision for going from stage 1 to stage 2) by setting a dip switch on the furnace board. This is for a moderate climate (Portland, Oregon). Would a multi-stage thermostat be better? (Why?) Which one would you recommend? (Honeywell Vision Pro 8000 ? - specific model?) Thanks.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Honeywell IAQ thermostat.

    Why cripple your furnace by using a timer. And not getting all the comfort you paid for.
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  3. #3
    Join Date
    Nov 2010
    Location
    Portland, OR
    Posts
    14

    Exclamation More Details please

    Are you referring to the Honey Pro Vision series? What additional functionality does it provide and how does that enable one to better exploit the capabilities of the 2 stage furnace?

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    The IAQ is a Honeywell Pro series thermostat.

    It will determine when the homes heat loss has reached 90% of the furnace's first stage . And then bring on second stage. So it will provide more comfort. Not have short cycles due to timing into second stage needlessly.

    Can slow the VS blower when the indoor humidity is high in the summer, if you have A/C also.

    The IAQ can be set to time to second stage after X minutes if you really want. Personally, I don't recommend using it though(the timer function that is).

    It can also control a humidifier if you have a whole house humidifier on your system. It has many abilities.
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  5. #5
    Join Date
    May 2008
    Location
    Portland, OR
    Posts
    236
    Hello Joelltzx,

    Great choice of furnace!

    I would definitely upgrade the thermostat to get the most out of the new system. The Honeywell IAQ is a great choice to control the variable speed fan.

    What size system are they recommending?

  6. #6
    Join Date
    May 2010
    Location
    West Chester, PA
    Posts
    177
    Quote Originally Posted by beenthere View Post
    The IAQ is a Honeywell Pro series thermostat.

    It will determine when the homes heat loss has reached 90% of the furnace's first stage . And then bring on second stage.
    If we assume the first stage is 70% of second stage, 90% of first stage would be 63% of second stage. So when the thermostat calculated heat loss is >= 63% of second stage and it needs to call for heat, how does it issue the calls? Does it simply call for high stage? Does it call for low, then high, then low... attempting to blend in the minimal amount of high necessary to meet demand? Something else?

  7. #7
    Join Date
    Jun 2009
    Location
    Albuquerque NM
    Posts
    2,485
    Quote Originally Posted by RandomNick View Post
    If we assume the first stage is 70% of second stage, 90% of first stage would be 63% of second stage. So when the thermostat calculated heat loss is >= 63% of second stage and it needs to call for heat, how does it issue the calls? Does it simply call for high stage? Does it call for low, then high, then low... attempting to blend in the minimal amount of high necessary to meet demand? Something else?
    Most 2-stagers are 65-75% of max output on low. The HW IAQ doesn't know what the actual 2nd stage output is, as a percentage of maximum. The stat just calculates when it thinks the furnace is putting out 90% of it's 1st stage capacity, then calls for 2nd stage (it's on a separate connection). I suspect this stat uses what it knows, temperature rate-of-change and run time, to decide when 90% of the the 1st stage is being used. It doesn't know the actual output of the furnace on 1st stage, or the heat loss of the house, so it can't use that to decide.

    I beleive that some of the IAQ stats (like the Prestige) will also downstage if you set them to, or finish on 2nd stage if you want that. If you look at the doc for the Prestige this is the setting for "Finish on High Heat Stage". Not sure if all 2-stage furnaces will downstage once the call for hi-heat is removed though. It is going to depend on the logic in the furnace control board.

  8. #8
    Join Date
    Nov 2010
    Location
    Portland, OR
    Posts
    14

    Lightbulb

    100K BTU (largest one) 95% eff to replace 138K BTU 80% eff Carrier.

    Am not replacing my Honeywell Electronic Air Cleaner as it caused lots of problems (Honeywell circuit board blew a fuse and fried several wires in the furnace - TV sets went nuts, zapping like Frankenstein's lab when furnace went on). Any suggestions on filter systems, MIRVs, etc. or just use what it comes with? Honeywell system didn't seem to catch much in the way of dirt.

  9. #9
    Join Date
    May 2008
    Location
    Portland, OR
    Posts
    236
    100k BTU? You must have a HUGE home! Most furnaces in this area are 60k.

    If allergies or asthma are not an issue in your home, I would recommend the Honeywell F100. It's a 4" filter that catches a lot of stuff and only needs changed once a year.

  10. #10
    Join Date
    Nov 2010
    Location
    Portland, OR
    Posts
    14
    4200 sq ft heated - mostly vertical on three living levels built into the side of a hill (2 levels above ground), with another unheated storage level below. Due to view setting (trees, creek, etc.) most large windows face North-ish.

  11. #11
    Join Date
    May 2008
    Location
    Portland, OR
    Posts
    236
    100k sounds about right for that size house. I would still recommend a heat load calculation.

    With three levels, do you have any problems with rooms that are too hot or too cold?

    Have you had the duct system cleaned recently?

  12. #12
    Join Date
    Nov 2010
    Location
    53203
    Posts
    24
    I'm looking for a 2-stage thermostat for heating with a Rheem RGRL or RGRM furnace. I don't want anything that involves a timer, would prefer something that makes a decision on stages by determining how many degrees from setpoint that the room is. Also would make sense if it ramped down to the low stage when within a degree or 2 of setpoint. So far, when I've researched models online, there is very little explanation of the actual function of each. Most speak in vague and sensational terms about $$ savings, etc., but not about function. Even some heating contractors did not have an understanding of this concept, so I want to make sure I get this figured out.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    The IAQ.
    It won't let the temp drop by 2 degrees though.
    It will how ever, bring on the second stage, when it determines that the house's heat loss is at 90% of first stage's output(except during recovery from set back).

    It will go back to first stage as the temp gets closer to set point.

    CPH setting help to get it to cycle the way you want, within reason.
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