Low cost outdoor thermometer

I want to be able to turn on my gas logs automatically whenever an indoor thermostat is calling for heat AND an outdoor thermostat says the temperature is below a temperature selected from a range of 25 to 40 degrees F.
I am trying to find a low cost termostat for the outdoor portion of this system. It can a simple mechanical thermostat with a SPST switch closed when below set point or a SPDT switch.
Any pointers would be very much appreciated. I have not been able to find anything on the web.
Thanks!
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On 12/13/2010 13:02, snipped-for-privacy@aol.com wrote:

For a cheap way of doing this, consider cannibalizing an old refrigerator for a thermostat. This may require some additional control circuitry as a typical refrigerator thermostat contact OPENS when the temperature falls below the set point.
A few other words of caution: Are the gas logs designed for room heating? Typically they're just for show. Are they designed for automatic unattended operation with a pilot safety relay or automatic ignition with no-flame cutoff? Is there a high limit switch as exists on heating appliances? These potential dangers, as well as self-interest protection measures from the HVAC industry, limit the availability of these devices to the DIY hobbyist market.
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All good points. Thanks.
I did not mention that, in addition to the thermostats, there would be a switch to select between     unconditionally on     auto (use the thermostats)     unconditionally off (used when unattended) Yes the gas logs are intended for (and do a great job of) heating There is low oxyget and CO protection.
Using a refrig thermostat would require a relay and I wonder if I could get the necessary temp range since it crosses freezing. A refrig shouldn't go lower than freezing and a freezer shouldn't go higher so they MAY not be made for the desired range???

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On Mon, 13 Dec 2010 19:02:25 -0500, snipped-for-privacy@aol.com wrote:

Omega will sell you a thermostat that can do just about anything you want but they ain't cheap. There are some low cost thermostats used for stock tanks and such and you can find them at a good feed store.
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Thanks! I didn't see anything like this on Love Controls' web site, but I sent them an email asking if they could provide one or suggest another source. I noted that they sell thermocouples and my gas log circuit is powered by an alreadt existing thermostat, so perhaps they can help.
wrote:

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On Dec 13, 7:02pm, snipped-for-privacy@aol.com wrote:

How about an old mechanical thermostat, perhaps you can change it's orientation to cover your desired range. Or remove the insides and play around with another mount. The bimetal spring should continue to contract and expand across the freezing mark.
Vented gas logs are not particularly efficient but if you have a fan in them they do make some heat. Unvented, well I wouldn't use those myself.
I don't have any problems buying anything other than complete furnaces or acs from the local hvac supply houses. Just know what you want before you walk in.
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I thought about that and may still go that route. I do not have access to an old thermostat, so I would have to buy one. I kind of hate to do that since I am not sure I could make it work.

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On Dec 13, 7:02pm, snipped-for-privacy@aol.com wrote:

So is this indoor thermostat dedicated to just the gas logs, or is it controlling your primary heating system and you wish to use it to control this additional heating source as well?
Typically the low voltage thermostats require using some sort of relay to control line voltage motors and starters in furnaces, you are just not seeing them because they are on the control board...
Your description of the "control switch" is a standard HOA (Hand/Off/ Auto) contactor controller which will involve the use of a relay and a contactor to control said devices with a standard low voltage wall thermostat...
How to do this using a "low cost" outdoor thermostat? Good luck... Weather responsive heating controls are not known for being cheap...
~~ Evan
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The gas logs provide a pair of contacts. Shorting the contacts together will turn on the logs. This is powered by a thermocouple having one end in the flame. Therefore, the circuit is very low voltage & very low current. The contacts of any thermostat could be used in this circuit with no problem.
The overall idea is to keep the heat pump from running when the outside temp is low enough to make using the heatpump more expensive than using the propane logs.
I would have a separate indoor thermostat for the logs set a degree or two higher that the thermostat for the heatpump. As the house temperature falls, the gas log thermostat whoud start calling for heat. If the outside thermostat says it is cold enough out there, the gas logs would come on raising the temperature in the house & thus preventing the heatpump from coning on (unless the logs couldn't produce enough heat - but that hasn't been a problem).
If iw was too warm outside for the outdoor thermostat to close, then the house temperature would continue to fall another degree or two and turn on the heat pump.
Really a simple arrangement. Any thermostat with the proper temperature range should work fine. I could enclose it in a waterproof plastic bag if I had to.
On Tue, 14 Dec 2010 22:30:15 -0800 (PST), Evan

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Look in beer brewing equipment.
Steve
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On 12/13/2010 3:02 PM, snipped-for-privacy@aol.com wrote:

Google differential thermostat. Good luck with low cost.
LdB
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On Dec 13, 5:02pm, snipped-for-privacy@aol.com wrote:

Your thermostat may already have what you need. Mine did. My heat pump had a second set of contacts that could control an alternate heat source when the outside temp got down to about 40F. For me this also limits heating to the core of the house which saves me money and I like sleeping in a cold bedroom with lots of quilts on the bed.
Jimmie
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