Two thermostats in parallel on simple heat-only system?

My fancy new programmable thermostat takes batteries and of course if the batteries fail (or any other fault develops with its electronics) then we'll have no heat. Bad news for the pipes and the cats if that happens when we're out for a week mid-winter. So I'm thinking, can I wire the old round Honeywell up somewhere else in the house, electrically in parallel with the new one, and leave it set on some low safe temp, so if the new one fails, the old one will keep the house from freezing? Or will this mad scheme damage something? I figure thermostats are just switches and if two are in parallel, either will close the circuit; even if both are closed at once, no problem.
This is a two-wire system, heat only, newish high-efficiency sealed-combustion gas boiler with circulator. The old Honeywell has a heat anticipator, which I'd set to low or off. The new one, I think, uses digital logic for that function so *I assume* draws no current when not calling for heat.
Thanks for any advice,
Chip C Toronto
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the batteries are for backup only. The furnace supplies power to the t-stat under normal situations. Even if the batteries fail as long as you have power the t-stat will function. To me sounds like more work that it is worth.
Change the batteries every heating season and you will never have a problem.
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Absolutely fine idea. No problem at all

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Redundancy is a good thing. Sounds like a good idea.
one caveat though, remember to tell others in the house, or if you should ever sell, let the next owners know. I could see someone pulling their hair out, trying to figure out why the &*$%# thermostat won't work right. <LOL>
AMUN

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Chip C wrote:

I think you are approaching the problem from the wrong direction Chip.
If you are leaving the house long enough for it to freeze up if the heat fails, then you really should have some system to alert someone to come an fix whatever's gone down.
There are inexpensive temperature operated dialers available which will call several different telephone numbers of friends, family or your heating contractor who have been given access to the property, and play a recorded message telling them that the place is getting cold.
If your budget permits, central alarm companies who do burglar and fire monitoring also offer low temperature alarm monitoring and notification.
Way back when, we just used a line voltage rated thermostat to turn on a red lamp in a front window if the house got too cold, and the neighbors would pitch in to help if they saw it lit.
You should also think about shutting off your main water valve when you leave the place empty for more than a day to avoid serious water damage to the place if you do get a freeze busted pipe or something like a water heater or a washing machine hose decides to blow while you are away.
I learned all that through experience. (The best kind to have, my next door neighbor's, not mine. <G>)
My neighbors of nearly 20 years moved to a nearby state in the fall of 2002. They put their gorgeous home on the market for $1.8 mil. and took no precautions about freeze ups. The house didn't sell quickly and one morning in January 2003 I looked out a side window and saw this:
http://home.comcast.net/~jwisnia18/temp/freezer.jpg
That's heavy columns of dirty brown ice coming down the front of that garage door.
I had the unpleasant task of calling my old neighbor at his new location to tell him his oil heat must have quit.
It took all of 2003 and the spring of 2004 for them to battle things out with their insurer and then have contractors rip out and replace half of the first floor of that house. They hauled away three of those big "roll on" containers of ruined house guts. The place went back on the market in the summer of 2004 but still didn't sell.
Guess what happened in January 2005?
Right, a pipe froze and burst again. I found out through a phone call from the ex lady of that house, telling me she knew already and asking me not to call her husband about it as he was recovering from heart surgery.
They only needed one "roll on" container to hold what they ripped out this time and the repairs were completed by summer. The house went back on the market, but word must be out and maybe potential buyers are scared off by the possibility of mold, because the price has trickled down to $1.3 mil already.
Some guys never learn, do they?
Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat \'57 EE)
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The batteries are there to "save" your program in case the power goes out. The drain on the batteries is so low, the batteries would probably last 6 months to a year. Best thing to do is change the batteries at the beginning of the heat season and you won't have any problems.
OTOH, if the power goes out long enough to kill the batteries, your pipes and cat are going to freeze anyway.....
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Dr. Hardcrab wrote:

Actually, this might not be totally true. I have a Honeywell programmable and the batteries actually run the entire unit. Typically there is no "return" line for power in a thermostat, especially in a 2 wire system. Sure, you could draw some current from the 2 wires when the stat is off, but that's not too good, especially in the older furnaces that control the gas valve directly. I have seen some stats that do this. They can actually draw enough current to keep the gas value open just a little. I had this happen with an earlier Honeywell unit. Honeywell admitted this was a problem and replaced the unit with one that has a small relay in the unit to close the connection and open the gas valve. BTW, the only current drawn by the anticipator is when the stat is on, as it is in series with the switch.
This all said, you could still run them in parallel setting the old mechanical unit to a lower emergency temperature and the new one to a higher, normal temperature.
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More like 3 years for alkalines. You stand a better chance of having them LEAK and corrode the battery contacts in the TS.

that would go a long way towards preventing leakage damage.
--
Jim Yanik
jyanik
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HI CHIP
YES YOU CAN PUT ANOTHER THERMOSTAT IN PARALLEL WITH YOUR BATTERY OPERATED ONE THIS WILL WORK. WHEN THE BATTERY ONE FAILS THE ROUND T87 THERMOSTAT WILL CLOSE THE CONTACTS TO OPERATE THE HEAT.GOOD LUCK
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This is Turtle.
Bob , Awwwwwww Are you Deef or is your cap lock stuck ? You might want to make regular letter to type here with so we can hear you better.
TURTLE
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Years ago, when I worked for Sears, the guy training me wouldn't let me jump the furnace end of the thermostat wiring. Had to pull one of the wires, and then jump the terminals remaining on the furnace board. He said that simply jumping the connections would burn out some thermostats.
Well, that was 9 years ago, and I'm still not sure why. No one explained why (back then) and I havn't heard anything convincing since then.
Your double thermostat idea sounds good to me.
--

Christopher A. Young
Do good work.
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This is Turtle.
Fine ideal with the dual thermostats !
now one thing to think about here. When a Honeywell thermostat batterys fail. they fail but the hvac system should still keep the heat or cooling going as set when you left. the screen will go blank but it should keep running as it did as it was with batterys in it were good. The thermostat batterys are really for control out put to let you see what is going on but will still keep working. the system works off the 24 volt power system and not the battery power system.
Another one for you to concider : Most all Honeywell batterey type thermostats will warn you about 1 to 2 months as to being low on battery level. they will come on the display screen and say low battery about a month or two before they go out.
TURTLE
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"The thermostat batteries are really for control out put to let you see what is going on but will still keep working. the system works off the 24 volt power system and not the battery power system."
Don't know what brand of thermostat the neighbors have but it will not work when the batteries go dead, no furnace, no heat.
Walt Conner
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This is Turtle.
Heat will work even after the thermostat tells you the batterys are low and will warn you 1 to 2 months before it goes out.
then when you don't change the batterys like you should or have been told to on the screen of the thermostat. The heat will still work about 2 to 3 weeks with battery just about dead and screen goes out. honeywell will still work as to keep what it was set on when it went out for a good while months with the screen dead.
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So it tells you your battery as bad / low and does this 2 months before it dies.
then when you wait till the screen goes out. It will still run the heat 2 to 4 weeks after that very possibley longer.
Now if you can't figure out there is something wrong when the screen goes blank and has been blank for 2 weeks or longer. LORD help you !
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Now Honeywell will do this but other brands i don't Know.
TURTLE
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On Mon 29 Aug 2005 10:10:01a, Chip C wrote in alt.home.repair:

Your idea should work, but what I want to know is, what do the cats have to eat if you're gone for a week at a time? I'd be afraid they'd starve before they froze.
--
Wayne Boatwright **
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snip
HAve you checked by reading the instructions to see if your stat has a failsafe freeze protection on it? Every single digital stat we sell has this feature...if for whatever reason the batts fail, or the programmings off, or if you just turn it off and forget it, it will maintain a 50F temp. Now..if the transformer in the unit fails, your gonna freeze.
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Many thanks for the advice from all.
To answer the several very good points that came up:
- We do have a catsitter come in every couple of days while we're out but it's not her job to diagnose hvac problems and besides, in a real cold snap we could have frozen pipes in less time than that, I think. It's the rads I'm worried about.
- The new unit is a Honeywell Chronotherm IV. The manual says that when the batteries are dead, there will be no heat, so that's what I'm going by. But the batteries are just part of the story, I figure that an electronic gizmo has lots of ways of failing besides batteries.
I'm really glad to see Turtle is still posting. I hope you're keeping well, Turtle.
Chip C Toronto
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I am unhappy that Honeywell stopped making the Chronotherm line. I have a Chrono III that has been performing well for quite a few years.
Now they are making the Touchscreen units. Have only installed one so far. We'll see how well they work.....
http://yourhome.honeywell.com/Consumer/Cultures/en-US/Products/Thermostats/Programmable/Do-It-Yourself/7-Day/Touchscreen/Default.htm
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