Space Heater Electrical Question

Hi Everyone

Please help fight my ignorance.

My wife is looking for an electric space heater for a small room where she likes to read. The whole floor is on one zone, and we don’t want to heat the area just for this small space.

She is seeing a number of units advertised as 15A, 1500W. Now, I always thought that a space heater shouldn’t draw more than 75% of the circuit, for safety and in case someone should flip on a light or similar.

I haven’t purchased many space heaters, but I do seem to recall that the occasions when I have the largest 110V units I saw were about 1100 watts, which gels with the above.

My question is whether I was mistaken about what I thought was a rule (as opposed to guidance), or whether this is a case of legions offshore Amazon sellers peddling product that hasn’t been designed to proper standards.


What year was your house built?

This wattage is okay for a modern home, wired correctly.

No extension cords, okay?

First of all, 15A is 1800W, so something isn’t adding up.
If the heater is actually 1500W, that’s 12.5A, which is what a typical Vacuum cleaner is rated at.

Many houses are wired for 20A. 15 amps is 75% of that.

Yes. I always figure 10 amps per 1,000 watts; first, because it’s easier, and second because I like a margin.

Wow- some quick replies!

First, I always thought one used 110v in these calculations, but I see beowulff is using 120v. Given that there is variability location to location, and even day to day (at least, in my experience) which is correct?

Second, to JohnnyLA: Most modern homes seem to have some 20A circuits- my house from the 80s has them in kitchen and garage, but it has not been my experience that all the circuits are 20A. Besides, the units are advertising as OK for 15A circuits and 1500W, not advertising that they produce 1500W @ 15A.

But nobody’s mentioned the 75% at continuous load rule- did I imagine that?

Perhaps the element uses 1500w, but the entire heater requires 15a. Many space heaters have a motor (to oscillate), a fan and some sensors and electronics on board.

Could also just be a typo or some kinds of miscommunication somewhere between the technical team that built it and OldOlds posting it here.

I recently bought an oil-fill space heater that is rated for a maximum of 1500 watts. However it has three settings and only the highest uses the 1500 watts. It does a very good job of warming up a small room on the lowest setting. Of course an oil-filled space heater takes a while to warm things up. On the other hand they are less of a fire hazard and there’s less chance of someone getting burnt touching one.

I’d recommend getting an oil-filled space heater with multiple temp settings. Then tell your wife to not put it on the highest setting.

That’s electrical code for dedicated circuits. Electricians need to follow it, not you.

I did a lot of shopping for major appliances in 2014. My observation is that manufacturers no longer advertise the actual draw of the appliance in amps. Instead, they advertise the capacity of the circuit they want you to plug it into.

Go to your favorite appliance store web site. Check out the refrigerators. Click on the manufacturer’s specs pdf file. For typical residential refrigerators, they all say “15A” whether it is a tiny apartment frig that’s Energy Star certified or a huge designer unit that’s not. They all say 15A. That can’t be the real draw.

You may be seeing the same thing happen with portable heaters.

This is the only type of heater to purchase, but be sure that it has a tip over switch that shuts it off if it gets tipped over.

Deleted, not relevant.

I am not an electrician but I am a retired HVAC tech.

I wonder if the heater does produce 1500 watts but the 15 amp part is just so the homeowner knows he can use it on a standard 15 amp circuit. If that is the case, it likely draws 12.5 amps at a nominal 120 volts. Now a 15 amp standard breaker should only be loaded to 12 amps (80 percent) for a continuous use application, so I guess the manufacturer is fudging a bit or he is using 125 volts for his calculations. I have no idea how much leeway he is allowed there. (I just looked up what constitutes “continuous use” and it is when a maximum load is expected to continue for 3 hours or more.)

And I too have an oil filled heater for a room that needs a bit of help. I never use it on its high setting because I just don’t want to push my luck.

That’s possible, and maybe not even intended. The numbers in consumer appliance specs can be pulled from anywhere, and their accuracy is limited. Anyhoo… 1500 watts is all you should have plugged into a line for safety, especially with something like a heater. Not only is there a lot of resistive heat produced, the cheap units conduct a lot of heat down the wires which adds to the fire hazard.

For safety have no papers,books or clothes close to the heater.

How hot it gets does not matter but things close to it does matter.

Nothing should be close to it for safety.

And books,papers and clothes are very bad.
If it gets too hot you could burn you self if you touch it.

I know this is a little off subject but this is very important. Extension cords should only be used when absolutely necessary. And always buy the heaviest cord you can get. That goes for everything.

It depends on the size of the room. A quartz heater would be better for short term uses where it would heat the person and not the room. If it’s truly a small room and the op wants it a steady temperature all the time then the oil heater would be a good choice. Particularly if the person is near the heater. .

Match the heater to the task.

We have decades of experience with various types of electric heaters and the oil filled heaters are the best. We have three. They have no moving parts so are very quiet and have about 15 square feet of surface area. Usually, there are three settings of ~400, 900, and 1500 watts. We run these off 15 amp circuits. You can run them at 1500 watts with lights on from the same circuit, but most of the time you will want to have them on low or medium. We have also run two on the medium setting on the same circuit, if we are heating different rooms on the same circuit, although if you forget and turn on too many lights, the breaker will trip, but that is not a big deal. When you first turn on a new heater, it will give off fumes, apparently from oil residue left over from manufacturing. You will want to run it away from living space at 1500 watts with the thermostat set to maximum for a day or so to burn away those oils. A garage is a good place to do this. This will also give you an idea how much heat these things crank out. You will not be disappointed.

I have bought mine on ebay. Here are some examples.