Low Voltage Thermostat on 5kw Farenheat Heater


Old 01-14-15, 10:32 PM
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Low Voltage Thermostat on 5kw Farenheat Heater


I have a Farenheat FUH54 240V 5kw heater in my attached 20x20 garage. It's connected to a 30A dual pole breaker with 10ga wiring. Over the past week the heater has acted up a few times and failed to shut off, turning my garage into a 85 deg sauna (temps about 15deg in IL). The thermostat feels like it is reacting correctly when the pot is rotated, but even in the off position it would not turn off. Once I flipped the breaker off and back on the heater worked fine for 3 days and did the same thing again. Does this seam like a faulty thermostat or could it be something else?

I have it ceiling mounted and it's a pain to adjust the temp. I'd like to install a RT850T relay with built in transformer so I can use a 24V low voltage thermostat for easier access and better temp control. I'm assuming this would be wired in at the wall junction box and then wiring continued to the heater?

Right now the SPST thermostat connects between the L1 terminal and the wattage terminal board. Since I will now be using an external thermostat, could I just run a jumper between the two terminals to remove the old thermostat or am I better off to just leave it and turn it to max heat?

If I do go with a low voltage thermostat, is there any way to keep the feature that delays fan operation until coils are hot and keeps the fan running after the coils are turned off? Would that require wiring the RT850T after running power to L1 & L2 in the heater itself.

Appreciate any feedback on the best circuit location to install the new thermostat and either confirmation of bad thermostat or other ideas on why it randomly gets stuck on.


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Old 01-15-15, 12:33 AM
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Welcome to the forums.

Great idea with the RT850T. I would mount it right to the case of the heater. Connect it internally so that it replaces your heater mounted thermostat. It will maintain your blower operation as it is now. Circuit wiring below.

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Old 01-15-15, 07:33 PM
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Thanks for the suggestion. That thought had crossed my mind today. I ordered the RT850T and will give it a shot. Makes sense to replace the old thermostat to maintain functionality.

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