Everything you probably want to know about the DR-966
The heater requires a 35A circuit with #8AWG wire per Article 424 of the National Electric Code. The heater only pulls 25A on highest setting, but is considered a "fixed" device with a "continuous load", so the wiring and breaker need to be rated at 125%. That puts it at 31.25A, over a #10AWG wire and 30A breaker's rating. Don't risk your insurance company denying your claim if something goes wrong.
At that power, you don't want to use a line voltage thermostat designed for smaller baseboard heaters. If you want a wall mounted thermostat, look into any conventional thermostat, a 24VAC HVAC transformer, and a 40A 2-pole 24V HVAC contactor. I have three DR-966 heaters with their built-in thermostats all the way up and their switches on the 6000W setting, running off a single 24V transformer and Hunter 429999B thermostat, with a contactor near each heater switching the 240V AC on and off. If I'm not in the building I keep the thermostat at its minimum 45 degrees setting to prevent pipes from freezing. Using a contactor, you're essentially automating turning the heater on and off, no different than using the instruction manual's method of using the circuit breaker, and not voiding any warranty.
This is not an infrared heater, the manufacturer calls itself both Dr. Heater and Dr. Infrared Heater. The heater is a wire coil type, the front two coils are 1500 watts each tied together, the rear coil is a single 3000 watt for a total of 6000 watts. With the fan blowing on them, a spiral or two of the rear coil may get red, primarily near the coil supports. If the fan doesn't turn the coil will get red hot, and probably break the support wire inside and then droop. I received one heater that had a bent fan bracket not allowing the blade to turn and when powered up the rear coil did just that. I received a refund to buy a third heater and since the vendor was filing a damage claim, was told to discard the defective heater if after 10 days the shipping carrier didn't contact me to inspect it. After the 10 days passed without being contacted, I straightened the bracket out, verified the fan worked and then adjusted the drooping rear coil so there was a minimum of red spots. I ended up with 3 heaters for the price of 2.
Although the output of the heaters may feel like no more than a hand held hair dryer when your area is cold, follow the instruction manual's recommendations of keeping it the proper distances from walls and other objects. If you feel it isn't putting out like it should, use a clamp-on ammeter to verify the heater is drawing around 25A on each leg with the temperature control fully clockwise and the switch on 6000W. If it's not, contact the vendor.
I have a 30x50 pole barn shop with a 10' ceiling, so the roof peak is about 12'. It has "double bubble foil" insulation on the walls and roof, with exposed trusses. The heater's manual recommends 1.25 watts of heating per cubic foot, so 30' x 50' x 11' x 1.25W = 20,625 watts. With 18,000W of heaters, I can set the thermostat at 60, go to the home store 10 miles away and by the time I get back the heaters have shut off. If I already have my materials and I'm in a hurry to get started, I supplement the electrics with a 3-burner 45,000 BTU tank-mounted propane heater to raise the temp to 60 faster. So a single 6000W heater in an uninsulated 3-car garage may not be adequate.
Before I contacted the eBay vendor about the damaged heater, I contacted the Dr. Heater by phone. They told me they would send a replacement heater and pre-paid shipping label. Then I received an email stating they would email me a label within one business day and start the replacement process. I never received the label by email. When I called Dr. Heater on the second business day they said they would email a label by the end of the day. I never got that, so I resolved the issue with the eBay vendor, a 10 star solution. So it may not be worth the stamp to send in your warranty card. If you get a working unit, it's worth the money. Good luck repairing one later, since parts don't seem to be available. Due to one of mine having a bent fan bracket, if you get a DR-966 in the 160014xx serial number range, stick a screwdriver in the back and try to spin the fan blade before installation. A pallet of these might have gotten dropped on the dock after coming off a ship from China. If that bracket was bent before the heater was assembled, then don't trust the QC sticker on the back.
It hasn't got to zero outside yet, and I haven't got my first electric bill, so I may be in for a shock in that respect.
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