I have a garage electric heater (without thermostat) which I want to wire to a thermostat. The heater is rated 240 volt, 5000 Watt. First, can you suggest any particular thermostat that will handle this line load (I've only been able to find ones that handle up to approx. 3800 Watts) and, lastly, the correct wiring procedure. The heater is 2 wire (240V) with ground. Thank you

Does the heater have a built in relay or contactor?

Usually a large load such as this will need a contactor , magnetic switch,that would be controlled by a thermostat on a separate control circuit.

What is the make and model number of the unit you have?

The heating unit is a Fahrenheat ceiling mount Model #FUH 54B (17,065 BTU, 240V, 5000 Watt). It did come with a built-in thermostat which stopped working about a month after purchase. A replacment is unavailable so I by-passed the wiring to the thermostat and currently turn on the circuit breaker when heat is needed. I had wanted to wall mount a separate thermostat anyway because the unit is too high to reach by hand.

The wiring diagram shows that the power supply connects to a power terminal block (L1 & L2), then, internally, a "black" wire routes through the thermostat (black wire), then through a "Wattage change terminal board", then all wiring connect to the heating "Element", with "Hi Limit & "Fan Control" (through black, blue, yellow, & red - these are already in place by mfg.) with the " (through black, blue, yellow, & red - these are already in place by mfg.) with the " wirie back to the thermostat. I merely by-passed the " wirie back to the thermostat. I merely by-passed the " to and from the thermostat.

Please advise what I would need in order to connect to a wall thermostat (if possible). Thank you

I cannot find a line voltage wall thermostat that can handle more than 22 amps.

I suppose the one that was built into the unit was rated to handle more amps, guess not to well since it failed.

All I can suggest is to use a contactor to switch the line voltage to the heater, and have a single pole stat control the contactor coil. If the contactor has a 120 volt coil, then a 120 volt single pole stat is needed.

If the contactor has a 24 (twenty four) volt colt, then can use a low voltage stat, will need a 24 volt transformer.

There are a few stats on this page rated for 5000W 240 V:

Electric Baseboard & Line Voltage | prothermostats.com - programmable thermostats by Honeywell, White-Rodgers, Robertshaw, LuxPRO

I would forget the line voltage thermostat. For a proper double pole thermostat, you would have to run #10-2 to the thermostat, and then back to the heater.

If you don't have a neutral at the heater, you will have to find a 240/24 volt transformer, but then you can just run a cheap pair of #18 thermostat wires to the thermostat. Any old 24 volt thermostat will then work.

I also want more flexibility in my thermostat and have the same style and model heater(s) (I have 2 in my shop). On the face I see the answers to the respondent follow the initial logical paths. (you are running 240V - so you need to use 10-3 guage)... which is exactly what I thought initially too. But if you look at the wire going "through" the thermostat it is a light gauge braided copper (no more than 18 gauge - which is the standard thermostat wire for 24V thermostats). I have a tool that can measure the current and amps running through the wire when it is on... when I have more time and it is a priority I will relay the numbers which should provide more options. My guess is that we will see 240V running through the line but nowhere near the heating coil amperage. After looking at home improvmemt stores I am also going to make an educated guess that you could use the same thermostats used for baseboard heaters providing you can read a wiring diagram.