Recommendation On Single Pole Double Throw (SPDT) Thermostats

mtplus

I need SPDT thermostats for ceiling radiant heat in 40-year old home. They do not have to be programmable or digital. So far the only one I can find is a Honeywell T651A, which is not acceptable to the home owner.

Does anyone know of any others?

Thanks Robert

Doc

If you google ¨line voltage thermostat¨ you will find links to several good ones.Honeywell, White-Rodgers, and Lux Etc.

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mdshunk

Oh no you don't.

Single pole, double throw? No way, brother.

mtplus

mdshunk,

The Honeywell T651a has the following specs:
Specifications:

• Application: heating and cooling
• Temperature Range: (F) 44 F to 86 F
• Switching Action: SPDT breaks heating and initiates cooling on temperature rise

Notice the 'Switching Action' is SPDT. This is the only one that I have found so far but it is not aesthetically pleasing to the home owner.

Thanks for the feedback!
Happy New YEar!

Robert

mtplus

Doc,

Thanks for the reply. I have googled every known combo of line voltage thermos with no luck. I have already visited the web sites that you suggested including Federal Pacific and Hunter. No luck. These original thermostats are Federal Pacific.

happy New Year!!

Robert

mdshunk

Yes, but why do you need an SPDT thermostat for heating? I offer that you DO NOT! That thermostat is certainly SPDT, buy why in the world choose a double throw thermostat for heating????

mtplus

mdshunk,

Perhaps I have my terminology wrong. The radiant heat has 2 hots - inputs (110v). When I turn the thermo from off to on (40 degrees), neither input is connected to the radiant heat. When I turn the thermostat up, it will click when I hit room temperature and 1 of the inputs will be connected to the radiant heat. If I continue to turn up the thermo, it clicks again and connects the other 110. If I have defined the problem incorrectly, I would appreciate it if you could set me straight.

Thanks and Happy new year!!

Robert

SWCASH

It sounds like you need a two stage heating thermostat. Is your existing thermostat line voltage or low voltage?

mtplus

Swcash,
Current thermo is line voltage, 220 volt (2 by 110) for ceiling raidant heat.

Regards,
Robert

trollmaster

Does this unit heat up when 110 v is applied or only when 220 v is applied?If there is no heat untill 220v is applied then you will need a 220v stat.

mtplus

Trollmaster,

The radiant heat has 2 hots - inputs (110v). When I turn the thermo from off to on (40 degrees), neither input is connected to the radiant heat. When I turn the thermostat up, it will click when I hit room temperature and 1 of the inputs (110 volts) will be connected to the radiant heat. If I continue to turn up the thermo, it clicks again and connects the other 110 volts.

Regards,

Robert

trollmaster

When you have 110v on your first click does the tile start to heat up or will it only heat up when you have 220v applied

mtplus

The radiant heat begins heating with the first 110volt.

Robert

#CARRIERMAN

Hi mtplus

I believe that mdshunk was trying to relay that for 240 volt resistance heat you only need a SPST thermostat, a SPDT is typically used for heat / cool application. I am assuming that would be to code in your area. In this case one line goes directly to the element and the other runs through the stat. As far as a thermostat either way, the best priced place to get one is a Johnstone supply. If you have one in your area that would be the easiest place to see several types. I know they have the White Rogers version, thats the one I keep in the heat only and the heat / cool version. Couldn't tell you the exact part number or cost, I am not at work right now.

Good luck
Rusty

tyguy_104

Hi, I'm new to the site and am used to thermostats in buildings. I haven't been exposed to too many line thermostats though.

When the thermostat calls for 'stage 1' of heating the first pole (pair of contacts) closes and 110v is delivered to electric heater and is heating the room up. This is also known as a 'throw' ('throwing' on the electric heater).

If the room still doesn't heat up to setpoint, based on the thermostat's programming and inner workings (maybe 2 degrees colder than setpoint), then it will kick on 'stage 2' of heating and now closing the second pole, or pair of contacts, and now a total of 220v is delivered to electric heating and heating room up more quickly. Since 'throw' is defined from wikipedia as the # of positions a switch (or thermostat for that matter) can adopt (except off doesn't count as a throw) this is considered the second throw.

Technically with how you're describing the operation of your thermostat, I would technically consider it a double-pole (4 wire connections/2 pairs of contacts), double-throw (2 positions). DP-DT thermostat. I hope I got the terminology right.

As for electric heater's electrical: It will likely be served by a 2-pole 220v dedicated circuit breaker (can't speculate too much on amperage, but likely higher than 15 amps). Each pole of the circuit breaker is the same as each pole of the thermostat. 110v loads require a neutral wire, this is after the load and has nothing to do with your thermostat itself or any switching.

tyguy_104

Actually I'm reading more in depth on wikipedia and I changed my mind instead of double pole, double throw thermostat. I now may consider yours to be actually two individual single pole, single throw switches (one after another). It's confusing. Apparantly you call it single pole, double throw strange? On one site they say thermostats are either 2 wires (SPST) or 4 wires (DPST). They don't mention SPDT though. These terms get thrown around a lot it's hard to get an understanding of it.

beenthere

The OP is from December 2006, hope he found something by now.

MechAcc

Show the homeowner the tolerances on the T651 http://customer.honeywell.com/techli...0s/63-9173.pdf

Maybe they will reconsider.

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flashheatingand

Granted it's a post from '06, but nothing, a standard t-stat with a common peanut relay couldn't handle...

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DuMass

Yeah, old post or not, the OP sounded thoroughly confused about the system and how it works from the get go. All he likely needed was a HW 498B line voltage thermostat. It’s been around for decades. DPST 22A@240V and even has a marked OFF position for the required disconnecting means.
This is why I generally don’t like to offer advice to people who have no idea what they are doing. I used to be a licensed electrician in MD, so there’s no way that a Remodeler would be able to legally do any electrical work for a customer anyway.