My friend has asked me to help him install a 5000 watt /240 V forced air heater in his new garage. I checked it out and it doesnt say if it comes wired internally with a Tstat, or if you need an external on.

Couldnt find if it had a relay inside to control the heat. So What kind of options do I have for an external Tstat? Do I absolutely need a relay wired up to the tstat ?

Are there any industrial tstats good for 5000W?

Thanks!

I'm sure there's a relay in there, but if it does, it won't look like a standard relay.

Baseboard heaters often have a resistor-typr relay in them. Let me explain how that works:

The thermostat is usually an 18vac circuit. When the t-stat closes, current flows through the resistor, making it hot. This heat causes the contacts to close, and the heater begins to make heat.

Because of this method of working, there is a significant delay between the t-stat closing, and the relay itself closing. You can usually hear a 'click' when it does.

I found it most helpful to place a thermocouple, or thermometer, in the heater fins, so I could readily tell if the fins were warming up or cooling down.

Another variation will have a t-stat mounted on the face of the neater, with a 2-pole switch right behind the faceplate. These switches are misleading, and very easy to mis-wire. I reccoment using your meter to ensure you understand which contacts belong to which wires.

Adroga:
I believe that WW Grainger has a line voltage t'stat that is rated for 5KW at 240 volts.

I venture you are talking about a 5KW unit heater? Most mfg have a t'stat kit for their models, or a relay pkg to use a low volt t'stat

Or, if you have to be creative...a definite purpose 2 pole contactor/relay rated for 30 amp minimum, with a coil voltage of your choice, and a corresponding voltage rated t'stat should cover your needs.

Please check the Ca Electrical Code.

The only unit heaters of that size that I've ever wired called for a basic two-wire connection to the thermostat and like others have said, there is some form of contactor inside the unit. It is important that the feed not simply be controlled by a wall thermostat because the fan needs to be able to run after the heat is cut off. This allows it to cool down the element(s), just like with an electric furnace.

Thanks for the replies. I didnt even consider that the fan needed to run after the heating element cuts off.

Its a ceiling garage heater on sale this week.. not sure if I can post the link..

http://tinyurl.com/yzug8j8

There is no brand of tStat for this heater..

I imagine there must me some sort of contactor inside. If the tStat is built in then can it just be wired straight to the panel or does it need a safety disconnect? The subpanel in the garage feeding the heater is only a few feet away.

Thanks for the great replies!

Ed: (EV607797)

Good catch and important point re: fan run for cool down. I totally missed/forgot that

No problem, John. That's what we are all here for.



My guess would be that as long as the disconnecting means is within sight, then no, a separate disconnect isn't needed. We'll need one of our Canadian friends to confirm that to be sure. Also, you'll need to check the name plate on the unit or the manufacturer's specifications to see what their requirements are. Some may even require fusing in the disconnect, though I seriously doubt it.

If it plugs in or if the panel serving it is within 9 meters and in sight then it complies. Hard wired or out of sight requires a local disconnect simply because it has a motor in it.

get the unit. then the specs.

Then worry about the 'what ifs'.

No 'what ifs' can be answered with out the 'this is what I have'.

Sorry to come in so late on this topic.

I used to install a lot of locally-made "Avon-Air" heaters, ranging from 2kW up to 45kW.

Yes you will need a contactor or two in there.

One thing that no-one else has mentioned is a control circuit to cut the power to the elements, if the fan motor fails.

Mind you, you'd think that would already be in the "box", I did get caught once with this.

That wasn't an Avon brand heater though, it was something the Boss bought cheap.

Food for thought though.

Hey Guys,

My friend ended up buying a sylvania heater for the same price and exactly the same specs and similar heater. He was told to use a regular 5000w thermostat that he bought at a electrical dealer.

The heater has only a black,white and green wire. No contactor or space for one inside there.

We wired it up and it worked for a month or so. Now that its below o Celsius it trips every day apparently and the garage gets pretty cold.

I havent been able to go by and take a look, but I had him switch the wires in the thermostat in case we were cutting the wrong one and swap out the breaker.

I dont think the unit is faulty, might be a wonky breaker but might be the control set up. I dont see how a contactor would fit in there and if the fan needs to stay on after the temp is reached, there is no identification as to which wire controls the fan.

Other than getting a reading on how high the current draw is do you guys have any suggestions as to what to look for?

thanks!

Usually the fan is controlled by some form of temperature sensor within the unit so that control of it cannot be bypassed. It basically turns on whenever heat is sensed and doesn't turn off until the unit drops below the sensor's preset cutout temp.

This setup would require that the unit has power at all times and that the thermostat only controls the heating element. If it is tripping like you say (assuming you mean tripping the breaker), then there is more of a problem here than just thermostat wiring.

Its tripping with the thermostat on I believe.

If the unit is to stay powered at all times then how does the temp get set? The only switch is a on off switch that is also labeled fan/heat with stickers so its a little ambiguous.

I expected an internal setting for temperature and there wasn't, so leaving it powered at all times would be costly for a 5kw heater.

Even with a external contactor connected to the thermostat would yield the same results.

I will take another look and try and see if I can see anything else.

Would a thermostat with fan control be suggested?

I appreciate the help... many thanks

just to let you know that ironically it was a faulty breaker that caused this problem. swapped it out and the tripping stopped.

thanks for the informative responses.