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Old 08-22-2011, 12:11 AM   #1
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Not Enough Wires?


Hi!

Let's suppose I'm considering a new furnace ( well, actually, I _am_ considering a new furnace, to replace the one that was vandalized out of my new house ).

Now, it's tempting to get one of those two-stage furnaces. The climate here is very mild, and I bet it would mostly coast along in low burn. But on those rare days when it gets really cold ( by really cold, I mean 35F or so, with morning frost ) it would have some more oomph available.

But it seems to me that a 2-stage furnace would reasonably require another wire out to the thermostat. But as far as I can tell, there are no extra wires. What do you do?

As an electronics guy, I can imagine doing something with diodes - pull this one to ground, and current is pulled out of that one at the far end.... etc. With diodes, one wire can serve two different tasks. But that depends on being able to use DC on the wires.

If I wanted some real overkill, I could make a couple multiplex/demultiplexing boards with PIC processors and relay drivers. I have worked with these processors, they're very cheap and easy to use.

Another approach would be to have the furnace itself decide whether to go low or high, with a thermal sensor outside the house.

What do people actually do?

- JerryK

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Old 08-22-2011, 01:34 AM   #2
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Not Enough Wires?


So, what is your question again? As for the climate, It would probably be more cost efficient to go with a Heat pump, vs dual stage. I have a 2 stage furnace and single stage air, and the thermostat I use is a 3m Fitrete, which is a rebadged radio thermostat brand. It is one that I have found, that allows you to either do economy recovery, which is a longer time, before 2nd stage fires up, or fast recovery, which goes by the program the the circuit board in the furnace is set at, which is aprox 7 min's before it determines to go from 1st to 2nd stage.

The part about the wiring, it depends on how many wires you have avail. with the thermostat control wire from the furnace to the thermostat location. The most you would have, is 7 wires for two stage heat & two stage cool.

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Old 08-22-2011, 02:55 AM   #3
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many 2 stage furnaces do the switching inside the furnace,not the thermostat
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Old 08-22-2011, 03:35 AM   #4
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Not Enough Wires?


Quote:
Originally Posted by plummen View Post
many 2 stage furnaces do the switching inside the furnace,not the thermostat
Yes they can, but with a thermostat capable of doing multi-stage, you can adjust the program to be even more efficient. I am able to adjust the Swing & Differential programs on the one I have (3m Filtrete CT-50). I have it set for a Swing of 1.5, and Differential of 2 for both Heat & Cooling, which has made a difference in that the furnace is able to do its job properly. That with the two modes of recovery, you can "dial in", so that it also helps with being more efficient. On the flip side, I found out that with my home, I can not run the econ recovery, or dial in the diff at 4, due to when it was humid out last month, and the fact that I do not have any insulation in the walls, with the exception of our bath (something on the list, but have to wait to have the money to get it blown in), I lived and learned getting it dialed in for my system and home.

The better the thermostat and ability to adjust the running program, the better you make the hvac to do its job. I just found out the hard way during the first winter that we got our unit that year, the Single Stage White Rogers was not doing the job as I wanted, so while waiting on the WiFi capable thermostats to come down in price for the past 3 years, I had a Honeywell RTH6350 series. Only thing I loved about that one, was it would start the program for that period of the day, was that it would start a half hour earlier if I wanted it to. Also with the iPhone app for the thermostat, it gives me a way to change the settings, while on the go.

No, I love the 3m wifi one, because I can monitor the use through thermostatmonitor.com and run a background program on my netbook to be able to have local running info, and adjust the temp if I need to, or adjust the program, without having to stand at the thermostat. I have found that the 2 stage capable thermostat with the Lennox furnace I have is doing the job I expected it to. Now I am not in any way receiving anything in return for the two software programs, nor anything for the 3m thermostat, but I would rate all three pieces as very valuable, especially with the economy, and trying to squeeze every dime as tight as I can to save money in every way.

Looking at the stat's for yesterday, and last Tuesday, I ran the same number of cycles, but they were 54 min's different. Cost was 24 cents less for yesterday, with the system running at the same set points for day and bedtime. My average run time was 46.5. Cost was around $9.90. Now keep in mind, the only way it will track, is if I leave the computer up, otherwise the software does not track it, so it is pretty much from the time I have been up during the day, until I go to bed and shut off the netbook.
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Old 08-22-2011, 04:37 AM   #5
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Not Enough Wires?


Honeywell IAQ thermostat(YTH9421) only needs 3 wires at the stat. The EIM(equipment interface module) is mounted at the furnace, and that is where the additional wires the furnace has are connected.
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Old 08-22-2011, 05:50 AM   #6
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Not Enough Wires?


Quote:
Originally Posted by jerryk1234 View Post
Hi!

Let's suppose I'm considering a new furnace ( well, actually, I _am_ considering a new furnace, to replace the one that was vandalized out of my new house ).

Now, it's tempting to get one of those two-stage furnaces. The climate here is very mild, and I bet it would mostly coast along in low burn. But on those rare days when it gets really cold ( by really cold, I mean 35F or so, with morning frost ) it would have some more oomph available.

But it seems to me that a 2-stage furnace would reasonably require another wire out to the thermostat. But as far as I can tell, there are no extra wires. What do you do?

As an electronics guy, I can imagine doing something with diodes - pull this one to ground, and current is pulled out of that one at the far end.... etc. With diodes, one wire can serve two different tasks. But that depends on being able to use DC on the wires.

If I wanted some real overkill, I could make a couple multiplex/demultiplexing boards with PIC processors and relay drivers. I have worked with these processors, they're very cheap and easy to use.

Another approach would be to have the furnace itself decide whether to go low or high, with a thermal sensor outside the house.

What do people actually do?

- JerryK
Run a new thermostat wire with the amount of conductors needed plus an extra one or two for backup. It's no big deal.
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Old 08-22-2011, 06:54 AM   #7
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Not Enough Wires?


Yes, true 2-stage furnaces need both a first stage and second stage wire connected to a t-stat that has that function if you want to use the 2-stage functionality. The York modulating furnace I am looking can run off a single stage t-stat in which case the single heat wire makes the call for heat and the furnace itself varies output according to an onboard pre-programmed adaptive algorithm.

As noted above, it usually isn't hard to run another couple wires if needed... unless the t-stat is very remote through finished spaces. Luckily in my house the original installer ran a sheathed bundle that has several extra wires. Makes it possible for me to even run a 2-stage AC condenser without having to run an extra wire, which would be difficult.

Look at the install manual for your furnace where you should see the various t-stat connection diagrams for connection options.

Last edited by raylo32; 08-22-2011 at 07:00 AM.
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Old 08-22-2011, 07:23 AM   #8
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Not Enough Wires?


Quote:
Originally Posted by gregzoll View Post
Yes they can, but with a thermostat capable of doing multi-stage, you can adjust the program to be even more efficient.
[...discussion of Internet thermostat usage...]
*** This is *exactly* the sort of thing I have in mind. Since there are two systems, I plan on getting two CT30 radio thermostats. They're at the Home Depot for $100. They will talk to my Linux server, which runs 24/7. RTCA ( the people who actually make the thermostat ) has published the API ( Application Programming Interface ) for the thermostats. Perl scripts on the server can do pretty much anything you can imagine.

Now that I think of it, you don't even really need an outdoor sensor: weather reports for many locations ( especially airports ) can be automatically snarfed off the net by a script. Here's the current WX for
SFO ( San Francisco International )
KSFO 221156Z 27005KT 10SM FEW005 BKN007 OVC011 14/12 A3001 RMK AO2 SLP160

This means: On this observation on the 22nd at 1156 UTC,
The wind was 5 knots from heading 270 magnetic
Visibility was 10 statute miles
Few clouds at 500 feet
Broken ceiling at 700 feet
Overcast at 1,100 feet
Temperature was 14 degrees celsius
Dewpoint was 12 degrees celsius ( things are fairly damp)
Altimeter was 30.01 inches of mercury (relatively high pressure )

I got this by typing in a one-line command, which could just as easily be in a script.

- JerryK
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Old 08-22-2011, 07:46 AM   #9
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Not Enough Wires?


I have the 3M50 (same as CT30) radiothermostat and love it. I don't mess with coding for it but use the built in programming and web based connectivity via wifi. Works great and does have 2-stage heat and cool capability.


Quote:
Originally Posted by jerryk1234 View Post
*** This is *exactly* the sort of thing I have in mind. Since there are two systems, I plan on getting two CT30 radio thermostats. They're at the Home Depot for $100. They will talk to my Linux server, which runs 24/7. RTCA ( the people who actually make the thermostat ) has published the API ( Application Programming Interface ) for the thermostats. Perl scripts on the server can do pretty much anything you can imagine.


- JerryK
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Old 08-22-2011, 08:45 AM   #10
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Not Enough Wires?


Quote:
Originally Posted by COLDIRON View Post
Run a new thermostat wire with the amount of conductors needed plus an extra one or two for backup. It's no big deal.
*** This is a beautiful house. The sheetrock is flawless. I need to make every effort otherwise before I start buggering it up.

- JerryK
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Old 08-22-2011, 11:58 AM   #11
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Not Enough Wires?


Jerry, that is the one thing I would love with a control program, since with this thermostat, it is in the line of a budget mid-range connected home thermostat. Of course, there is always more than one way to skin the cat.
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Old 08-22-2011, 06:55 PM   #12
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Not Enough Wires?


I must be getting old. I just want the thermostat to come on and go off at a certain temp. No internetwifibluetoothwhatchamacallit crap attached.

.....

Now I sound like an old man that walked up and looked at his new touchscreen thermostat. He turned and looked at me and paused. "Son, if I had wanted a new tv, I would have gone to sears and bought one".
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Old 08-22-2011, 07:04 PM   #13
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[quote=Master of Cold;713101]I must be getting old. I just want the thermostat to come on and go off at a certain temp. No internetwifibluetoothwhatchamacallit crap attached.

I personally like the ability to track run times, cycles, and costs to run, especially with this Recession.
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Old 08-22-2011, 07:59 PM   #14
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Not Enough Wires?


Run times is the one thing the 3M50 (CT30) seems to lack. My ancient Hunter digital programmable that I replaced with the 3M50 did daily, weekly, monthly running totals of usage time. That was a nice feature.


[quote=gregzoll;713107]
Quote:
Originally Posted by Master of Cold View Post
I must be getting old. I just want the thermostat to come on and go off at a certain temp. No internetwifibluetoothwhatchamacallit crap attached.

I personally like the ability to track run times, cycles, and costs to run, especially with this Recession.

Last edited by raylo32; 08-22-2011 at 09:14 PM.
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Old 08-22-2011, 08:19 PM   #15
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Not Enough Wires?


raylo32, grab thermostat monitor at thermostatmonitor.com, and thermostat for windows at setyourthermostat.com. If you want to just pull up, you can pull the stats by IP/tstat/datalog through JSON. I used the Firefox addon to pull this:

http://192.168.1.68/tstat/datalog

{
  • -
    today: {
    • -
      heat_runtime: {
      • hour: 0
      • minute: 0
      }
    • -
      cool_runtime: {
      • hour: 7
      • minute: 57
      }
    }
  • -
    yesterday: {
    • -
      heat_runtime: {
      • hour: 0
      • minute: 0
      }
    • -
      cool_runtime: {
      • hour: 9
      • minute: 42
This data is only showing for the time I get up, until I go to bed, due to the computer has to be running 24/7 to get a more accurate set of data.
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Last edited by gregzoll; 08-22-2011 at 08:26 PM.
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