Space heater and circuit load


Old 11-20-18, 02:50 AM
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Space heater and circuit load

I will be purchasing a 1500 watt, 12.5 amp space heater. It will be plugged into a 15 amp circuit.

My knowledge of electricity is only rudimentary, but as I understand it, the maximum load for a 15 amp circuit is 1800 watts (15a X 120V = 1800w). However, if there is a continuous draw on the circuit for more than 3 hours (a continuous load), then the maximum load would be only 80% of 1800 watts, or 1440 watts.

Since the space heater is 12.5 amps, that puts its draw at 1500 watts (12.5a X 120V = 1500w), which will put it within the maximum load limit of 1800 watts for my circuit. However, even though I won't be leaving it on unattended or while I'm sleeping, still, during extremely cold weather, I will probably want to leave it on for more than 3 hours. This will cause it to be a continuous draw, which will cause its 1500 watt draw to be over the circuit's continuous load limit of 1440 watts.

My questions are: 1) Will the extra load after 3 hours be enough to cause a danger of either over heating or tripping the breaker? 2) How often should something be turned off and how long should it be left off so as not to be a continuous load?

Thank you
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Old 11-20-18, 05:06 AM
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Rule #1 for any plug-in space heater is: Be careful with it no matter what circuit size it is plugged into (even a circuit that has sufficient capacity).

Plug-in space heaters are notorious for over heating the receptacle where the heater is plugged in. I am not talking about the wire going from the electrical panel to the receptacle I am talking about the receptacle itself. The plug on a space heater many times will begin to heat up and cause melting of the receptacle that it is plugged into. Unfortunately the breaker does not sense this overheating because it is the receptacle itself over heating and not the wires going from the panel to the receptacle.

If you must use a plug in space heater as you said never leave it unattended, never leave it on while sleeping and you should check the plug every 10 minutes or so by grabbing the plug with you hand and feeling how warm it is. If it begins to get very warm or hot shut off the heater and pull the plug. Also, if using one be sure the receptacle is a good receptacle meaning that when you plug in the space heater the plug stays firmly in the receptacle and is not lose. If the plug is lose it will over heat easier.

My suggestion if possible is that if this is going to be in an area some-what permanent consider using a direct wired wall heater and running a new circuit. Far less chance of any problems.

And never ever use an extension cord or power strip (my opinion).
Old 11-20-18, 08:56 AM
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It will be plugged into a 15 amp circuit.

What else is on this circuit? Do you even know?
Old 11-20-18, 09:48 AM
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A 1500 watt space heater is designed to be used a 15 amp circuit. As long as you don't have any other big loads you are fine to use it.
Old 11-21-18, 08:42 PM
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Nothing else will be on the circuit - it is a dedicated circuit. It was installed a few months ago by a licensed electrician.
Old 11-21-18, 11:21 PM
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A 1500 watt heater is designed to be run on a 15A circuit. You are close to the 80% max circuit load but are ok. I would recommend using a spec grade or a pro grade receptacle for best connection to the plug.
Old 11-22-18, 05:01 AM
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I agree with PJMax about using a high grade receptacle for a very solid connection. But still, be aware that the plug can still get very warm even though nothing else is on the circuit. Just keep monitoring it.

Also a thought for the future. Since this is a dedicated circuit that you apparently had installed just for this reason of having a space heater plugged into it you may want to consider instead of using a plug-in space heater installing a hardwired direct connect wall heater. This way you do not have to worry about checking the plug or the receptacle over heating. One with a built in thermostat so you can even leave it on when not in the room or even sleeping. I added about 5 of these in my home to help supplement the main heating system for those really cold days like today where the high will be 19 and the low 4 degrees. I also find they are handy for the in-between fall to winter and winter to spring seasons where it is not that cold to run the main heating system so I run the wall heaters instead just to take the morning chills out of my house.
Old 11-22-18, 07:06 AM
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Have you looked at oil filled electric heaters. They warm the oil then cut off while the oil continues to warm. They have three wattage settings so you don't have to go all out at 1500w. I have used one for many years at 700 watts and find it works well as supplemental heat with out using electric continuously..

Big advantage is they are not a continuous load but you get continuous heat from the oil.
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