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Discussion Starter · #1 ·
Thinking about the setup of the 5000W Farenheit heater for the garage shop, it does have a simple knob thermostat, but since it will be on the ceiling, I would like to leave it set it to max and install another thermostat, programmable, within easy reach.


I have been searching for thermostats, and the higher en I can find is 22A. The 5000W heater at 240V, will draw a bit less that 21A. Are the 22A thermostats safe for this application or should I be looking for a relay?


Also, there are SPDT and DPDP models. Is it better to use the DPDT ones to kill both legs? Does it matter?


Anyone familiar with a good thermostat for this application?
 

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I think 22A thermostats are made/sized for the application, hence the number. That's chosen to fit on a 30A breaker (it requires a 125% derate, so that leaves about 1 amp to spare for control equipment).

You could also use a general-purpose relay/contactor that operates on a 24V coil, any common/cheap 24V transformer, and any 24V thermostat of your choice from a $20 Honeywell on up to the Nest.
 

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Thinking about the setup of the 5000W Farenheit heater for the garage shop,
Can I make a suggestion? I installed a Farenheat 5000w heater in my workshop.
It hangs from the ceiling. Is that the one you are talking about?

If so, here is what I did.
What I did is wire a thermostat remotely to the thermostat control circuit rather than cut the power with a larger thermostat.
What that does is allows the heater to have power after the thermostat is satisfied. That way the fan will continue to run until the unit has cooled down.
That allows it to operate exactly as the mfg. intended.
This is a more effective way of wiring the unit, and the control circuit draws much less amperage.
 

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Discussion Starter · #5 ·
Can I make a suggestion? I installed a Farenheat 5000w heater in my workshop.
It hangs from the ceiling. Is that the one you are talking about?

If so, here is what I did.
What I did is wire a thermostat remotely to the thermostat control circuit rather than cut the power with a larger thermostat.
What that does is allows the heater to have power after the thermostat is satisfied. That way the fan will continue to run until the unit has cooled down.
That allows it to operate exactly as the mfg. intended.
This is a more effective way of wiring the unit, and the control circuit draws much less amperage.

Yes, it is an FUH54. I had not though about the fan cool down. My initial idea was to use a 30A switch with a pilot, just to turn it on and off and note it was on. Then I thought it would be better to use a thermostat as the switch, but now I realize the problem with it.


Can you expand a bit on what you did? I assume the thermostat on the unit is a beefy bi-metal that handles the 21A, but there is obviously more to it because of the cooling. I have not seen the circuit. How does the unit do it?. Did you run two sets of 10/2 to the heater, one from panel to power it and one from the the thermostat to open contact ? What kind of thermostat did you use?
 

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I had purchased a Honeywell line voltage thermostat (YCT410B1000/U) because I had planned to wire it as you did. But after some research I decided I didn't want the fan to just shut off when the heater was still hot.
I did not purchase a programmable thermostat since I just turn it on 30 minutes before I get in the shop and it is warm enough to work.
I wired the heater per instructions with individual 10 Ga. wire. I was using conduit in the shop so I could keep all wires protected.
I ran some 14 ga. wire to the thermostat control circuit.
The control wiring is relatively low amperage unlike the line voltage.
I have not checked the amperage but the wires connecting to the thermostat on board are small. They are using a contractor to activate the elements so the thermostat only carries the load of the solenoid....very limited.
Although small, it is a 240 volt circuit.
If you do not have the heater yet you can get the installation manual online from Marleymep/com
 

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If it were me, I'd install a small 240 volt - 24 volt transformer and relay (both small cheap items) inside the heater (in electrical compartment) and let the relay (spdt or dpdt, either, whatever is easily available) interrupt the control wire of the 240 volt relay. That way you can run low voltage thermostat wire openly over to your standard low voltage thermostat (or line voltage, who cares). That allows you easily move the stat if you find your first choice of locations was not working as you like. The inspector will not likely question the fact that you have modified a UL approved device and if he does it's more defensible since your going out with a low voltage class 2 system that is low risk.

If you choose to run the 240 control wiring outside the heater and connect to a remote thermostat, you are on thin ice with NEC compliance, actually there is no ice unless you invoke the 25' tap rule (which the inspector may or may not allow). In essence you are running a tap conductor from a branch circuit (actually from another tap on a branch circuit, which is why the inspector may not allow it) and that, if allowed, requires you to land on protection based on the size of the taps, and the taps must be at least 1/3 the ampacity of the branch circuit breaker and blah, blah and blah brah it goes. Anyway, you get the idea, it's not easy, cheap or practical to do it that way unless you cheat. Legally you'd have to use #14 wire 30/3=10 amps) in metal conduit and land on a 2-pole fused or breakered disconnect before wiring onto a thermostat rated for line voltage. Then it must be no longer than 25' total wire length.
 

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And if you do as surferdude suggests it will open the door for just about any low voltage programmable thermostat.
Actually I may do it myself this winter.....I always look for winter projects.
Plus I have a few programmable stats lying around anyway.

The line voltage thermostat I am using is not the most accurate anyway.
 

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Surferdude...thanks for the suggestion.
I found a multi-tap 24v transformer on Amazon for about $13.50
Also found a RBM type relay for about $8.50
That is all that is needed.

If rdy2go wants to "go" this route I am sure we can get him there.

Now what should I do with the 240v Honeywell......sell it on Ebay? :vs_laugh:
 

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Surferdude...thanks for the suggestion.
I found a multi-tap 24v transformer on Amazon for about $13.50
Also found a RBM type relay for about $8.50
That is all that is needed.

If rdy2go wants to "go" this route I am sure we can get him there.

Now what should I do with the 240v Honeywell......sell it on Ebay? :vs_laugh:
That'll work! That relay is noisy but in the garage it won't be a problem.

Yep, sell that thermostat to someone that will use it on something that will never catch up and kick off so they won't realize that it has a wide differential. :wink2:
 

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Discussion Starter · #11 ·
I had purchased a Honeywell line voltage thermostat (YCT410B1000/U) because I had planned to wire it as you did. But after some research I decided I didn't want the fan to just shut off when the heater was still hot.
I did not purchase a programmable thermostat since I just turn it on 30 minutes before I get in the shop and it is warm enough to work.
I wired the heater per instructions with individual 10 Ga. wire. I was using conduit in the shop so I could keep all wires protected.
I ran some 14 ga. wire to the thermostat control circuit.
The control wiring is relatively low amperage unlike the line voltage.
I have not checked the amperage but the wires connecting to the thermostat on board are small. They are using a contractor to activate the elements so the thermostat only carries the load of the solenoid....very limited.
Although small, it is a 240 volt circuit.
If you do not have the heater yet you can get the installation manual online from Marleymep/com
So, all thermostat is providing is a contact closure via the #14, for the 240V you feed to the heater via #10 to circulate. That thermostat itself is not powered. Any contact closure thermostat could be used, but if it is electronic would need its own service. Looking at the diagram, it looks that all connections are in terminal blocks, is that correct? So it is a matter to remove the wires from the internal and replace with the external.


I am planing to hang the heater from the ceiling, following min clearance from wall, with a metallic box on the wall. I was trying to see if the inspector would let me take the NM-B exposed from the box to the heater, with proper clamps. I hate to have to make a short whip for the short distance. How do you have wired yours?
 

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Discussion Starter · #12 ·
If it were me, I'd install a small 240 volt - 24 volt transformer and relay (both small cheap items) inside the heater (in electrical compartment) and let the relay (spdt or dpdt, either, whatever is easily available) interrupt the control wire of the 240 volt relay. That way you can run low voltage thermostat wire openly over to your standard low voltage thermostat (or line voltage, who cares). That allows you easily move the stat if you find your first choice of locations was not working as you like. The inspector will not likely question the fact that you have modified a UL approved device and if he does it's more defensible since your going out with a low voltage class 2 system that is low risk.
That sounds like a good alternative.



If you choose to run the 240 control wiring outside the heater and connect to a remote thermostat, you are on thin ice with NEC compliance, actually there is no ice unless you invoke the 25' tap rule (which the inspector may or may not allow). In essence you are running a tap conductor from a branch circuit (actually from another tap on a branch circuit, which is why the inspector may not allow it) and that, if allowed, requires you to land on protection based on the size of the taps, and the taps must be at least 1/3 the ampacity of the branch circuit breaker and blah, blah and blah brah it goes. Anyway, you get the idea, it's not easy, cheap or practical to do it that way unless you cheat. Legally you'd have to use #14 wire 30/3=10 amps) in metal conduit and land on a 2-pole fused or breakered disconnect before wiring onto a thermostat rated for line voltage. Then it must be no longer than 25' total wire length.

I see things can get to be a bit complicated if you follow the NEC to the letter :sad:
 

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Looks like the best deal may be to get both from amazon so you get free shipping for >$25. There's something to be said for single source responsibility.

Transformer

Relay
 

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Discussion Starter · #15 · (Edited)
Looks like the best deal may be to get both from amazon so you get free shipping for >$25. There's something to be said for single source responsibility.

Transformer

Relay

When I fast read RBM in Missouri's post, my brain got RIB. Could you enlighten me? What is an RBM type relay?


I am not sure that transformer will fit in the heater electrical compartment. I wonder if I should put the transformer and thermostat by the service panel and run #18 to the heater. I may need 24V for something else.
 

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RBM is a relay manufacturer.
The name is used commonly to refer to small relays used in HVAC systems.

Think of it like a laminate countertop. Almost everyone calls them Formica, but that is just a brand name.

Steve, Emerson, White Rodgers all make a "RBM type" relay that will work.
They are all about the same size and wiring configuration.

I think the transformer that surferdude2 referred to will fit in the bottom of the heater, along with a RBM relay. You can power the transformer from your heater 240 feed, use the relay to replace the built-in thermostat then you can go to a low voltage programmable stat if you prefer. I am pretty sure I will go that route myself.
 

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Discussion Starter · #17 ·
RBM is a relay manufacturer.
I think the transformer that surferdude2 referred to will fit in the bottom of the heater, along with a RBM relay. You can power the transformer from your heater 240 feed, use the relay to replace the built-in thermostat then you can go to a low voltage programmable stat if you prefer. I am pretty sure I will go that route myself.

What power will the low voltage stat need? Are they always fed 24V from the furnace?
 

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What power will the low voltage stat need? Are they always fed 24V from the furnace?
Low voltage stats are usually 24 volts but there are stats available for millivolt systems. Some will work on both.
A heat only thermostat will be fairly inexpensive., once you get the relay and transformer installation configured.
 

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Discussion Starter · #19 ·
Low voltage stats are usually 24 volts but there are stats available for millivolt systems. Some will work on both.
A heat only thermostat will be fairly inexpensive., once you get the relay and transformer installation configured.
There is an aspect that still concerns me. How do you feed the #10 and the low voltage wire into the heater?



If it is just a pair for the stat, I see routing it to a metallic box close to the heater, to meet the #10, and from there, somehow, to the heater. But if the 24V needs to go out to feed the stat, then there are more wires and simpler to have the transformer outside.


What do you think?
 

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First wire up the 240 for the heater as you would anyway.
None of that is affected by the addition of the transformer or relay.

As far as the transformer and relay go, the best installation will have them inside the heater if there is room or attached to the heater on the outside. Either way the connections will need to be inside an enclosure for the transformer line side, not necessary for the low voltage.
If you can put both in the base of the heater....and from memory I think you can, then you can exit the heater with the thermostat wire via a knockout and a grommet. If there is no additional holes you can drill one and get a grommet to fit.
 
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