High- Or Low- Voltage?! - HVAC - DIY Chatroom Home Improvement Forum

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Old 10-29-2007, 01:12 AM   #1
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High- or Low- Voltage?!

First, I'm sorry if this is a duplicate post - I'vent seen another one, but if it's here please send me that way

I live in a condo unit with Hot Water Radiant heating. Popped into CT and got a High Voltage Noma (I know, I know...Student budget...) After much deliberation, I came to the conclusion that, as I only have a flow control valve in my suite, I should be using a Low-Voltage programmable. Back to CT, exchanged, paid more, all that jazz. Get the new one home, tear into the package, pop the old Honeywell mercury based one off and... two black wires, and two tied white wires...

This setup looks like a High-voltage deal, but I can't imagine what about it would be High Voltage?! Needless to say, I've no clue where to put the old wires into the new TS - spots for R/W/Y/G. Help!!

Should note that it's a Heat/Cool TS, but there's only heat in this building... someone, anyone... what goes where?! Am I using the wrong voltage?!

*Bangs head into wall*


Cypherson is offline   Reply With Quote
Old 10-29-2007, 07:39 PM   #2
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For all low voltage thermostats your R terminal is your power from your transformer, your W terminal is your call for heating, G is your call for the furnace fan, Y is your call for A/C.

Seeing as you are changing a mercury type stat, I would suspect you are using a low voltage set up. If the two white wires are tied together, I suppose you mean they are marretted or mechanically fastened in some other way. You will need to only attach 1 of the black wires to R and the other black wire to W and you should have it right. Just be sure you only have 1 R connection on the new stat. Some have Rh and Rc and that is for power to heating and cooling sections of the stat. In this case, you would want to hook onto Rh and W. Just remember the thermostat is just an automatic switch that is turned on and off by space tempurature, all you are doing is taking the power from the R terminal and putting it on the W terminal. with only 2 wires it shouldn't matter which way you hook up the two wires.
Hope that helps,


HVACDave is offline   Reply With Quote
Old 10-29-2007, 09:32 PM   #3
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After much late night prying to get the old Honeywell off the wall, and another few hours of trying to find the serial/model number - I've finally found it to be the Honeywell T822D1783. It's a 24V, as you said!

Long story short, wiring schema online looks like pretty straight forward, and with a cup of tea and some patience, it looks like the Y & G wires are for the cooling component (4 wire for a heating/cooling TS is something that still stumps me, but hey, I don't have a cooling system, so I'm ignoring them )

Black to R & W and I should have it done. This is a great forum, thanks for it, and the feedback!!!

If anyone in Vancouver with Hot Water heating in an Apartment or condo (from a boiler) is wondering... we're on Low Voltage (99% of the time... it only controls the zone control valve - that's my understanding)

Cheers & thanks everyone! Happy DIY-ing!
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