Saturday, June 3, 2023


RVelectricity: Avoid space heater danger: What you need to know – Part 1

By Mike Sokol

This is a special two-part article on a topic that’s not only seasonal, it’s very important to your safety, both in your home and your RV. This is about electric space heaters and how dangerous they can be if not used correctly. Be sure to answer the poll at the bottom of this story where we ask about whether you do or do not use a space heater in your RV.

Close to home

In 2017, in Hagerstown, MD, (my town, in fact) there was a house fire around 3 a.m. which resulted in the death of a mother and her adult son. Her co-workers said the victim used electric space heaters extensively in her house. She must have had a few close calls (small fires?) since everyone seemed to be worried about her using them to heat her house. The fire inspector reported that she had a portable electric space heater plugged into a string of outlet strips, and the wiring was covered in old newspapers. That’s a sure recipe for disaster.

Are electric space heaters really dangerous? Well, don’t just take my word for it. Here’s what says about them.

Why do we use them

Portable space heaters can be a quick way to heat up a room. However, they can be as dangerous as they are convenient if used improperly. These heaters cause at least 25,000 home fires a year, along with 6,000 emergency room visits, according to the Harvard University Environmental Health & Safety group.

Approximately one-third of all house fires nationwide happen during the cold home-heating months between December and February. Equipment that is intended to add a little extra warmth, such as space heaters, is the leading cause of these fires, according to the National Fire Protection Association (NFPA).

Are they dangerous?

So, exactly what can go wrong with an electric space heater that makes them so dangerous, especially in a confined space like an RV? In Part 1, this week, I’ll discuss the issues of current draw and in Part 2, next week, we’ll delve into flammable material issues.

It’s all about the watts, and the amperage needed to make those watts happen. If you remember some of the electrical math I’ve used in the past, wattage is simply volts times amperes (or V x I on this Ohm’s Law chart). That suggests we can divide the wattage of the appliance by the voltage and find out how many amps it draws.

Here are the numbers

A 1,500-watt space heater on a 120-volt outlet is 1,500/120 = 12.5 amperes. And an 1,800-watt space heater works out to 1,800/120 = 15 amperes. And while a properly installed and maintained electrical outlet should be able to sustain that amount of current indefinitely, few home (or RV) owners do routine inspection and maintenance of their electrical outlets.

If you do draw 15 to 20 amps continuously from an outlet, it can begin to heat up. That heating will soon cause the electrical contacts to oxidize and increase their resistance. And that resistance will increase the heating effect, which causes more resistance, which leads to something we engineers call cascade failure. That can eventually result in a char around the outlet itself and a potential fire.

How to know if this is happening? If the outlet your space heater is plugged into feels warm to the touch or has any dark marks around it, then the outlet contacts have been overheated and it should be replaced.

Danger, Will Robinson….

Importantly, NEVER run any electric space heater from an extension cord, especially a light-gauge one. Anything that draws 15 amps continuously needs at least a 14-gauge extension cord, and a 12-gauge cord is way better. That’s a really heavy extension cord for that little space heater. And never put two space heaters on a single outlet or extension cord. As you can see in my video, an overloaded extension cord can reach the boiling point of water easily.

Doing it safely

So what can we do to avoid electrical outlet overload and heat our RVs safely with electricity? First, if you need to use any space heater at all, use it on a low-wattage setting. I think that a 1,200-watt space heater or a 1,500 watt heater set on 750 watts is the largest I would use on a conventional electrical outlet, and even then it shouldn’t be run unattended. And make sure your smoke detectors are operational.

Safer solutions

Second, if you really need that much electrical heat (and it’s certainly cheaper than heating with propane you pay for yourself), then the CheapHeat product is a safe and effective solution if properly installed. The CheapHeat system is specially designed to be able to run continuously as part of your RV’s furnace, and since it’s hard-wired into your circuit panel there’s no electrical outlet in the current path to overheat.

Campground perspective

Do campgrounds actually welcome the use of the CheapHeat furnace system? At first blush you may think not, since it does cost them more in their monthly electric bill compared to everyone heating with propane. However, they really DON’T like electric space heaters simply due to the risk of fire.

So, if you plan to heat your RV electrically, then do it correctly with a hard-wired heating system that’s designed from scratch for the job. Also, I think that anyone installing a permanent electric heating system should consider upgrading their twist-lock shore power inlet to a SmartPlug, which has 20 times the contact area of an RV traditional twist-lock inlet.

A 10-second poll

Please take this short poll showing if you use a portable space heater in your RV. (It may take a few moments for the poll to load.)

Join me next week for Part 2, where I’ll discuss various technologies for space heaters including coil, ceramic and oil filled. Are any of these technologies more efficient or safer than the others? Tune in next week.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.


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Stephen F Willey
2 years ago

And watch out, many RV AC outlets use the “push-in” wiring, an easy way to install compared to screw terminals, but very small contact area for high current. We switched the outlet the portable heater plugs into to a high quality 20 amp rated screw terminal type.

Gary Stone
2 years ago

We use a small tip over-shutoff ceramic heater, but ONLY when we are awake and inside the camper…and plugged in directly to a good outlet. It never runs to keep us warm while we are sleeping…that’s what cozy blankets are for!

2 years ago

I use it most of the winter. If I plug into the RV power I never do more than low. I have a 12 gauge extension cord that I plug into the 30amp plug on the power poll using a dogbone to kick it down for the extension cord. I then run it through the window taping it so no cold air can come in. If I need high I feel safe this way keeping an eye on where the two plug together to make sure it doesn’t get hot. So far I rarely have used the heater on high.

Last edited 2 years ago by rvgrandma
Stu Spillman
2 years ago

I tell everyone to get 2 or 3 ceramic heaters and run on low heat on different circuits to avoid tripping breakers. It is safer and more even heat. I just tell them to never use an extension cord with a heater. Most do not know wire gauges and tripping over them is a hazard. Your advice is great as usual.

2 years ago

We use oil filled heater and never turn it to the full 1500 W Nd no extension cords

2 years ago
Reply to  Tom

Are the oil filled heaters safer than an electric ceramic space Heater for camper use? They seem to have more even heat and longer residual heat in my house basement. We don’t use extension chords there but may use a 10 or 12 guage one in the camper.

We already have a propane ceramic space heater that is available in case of power outages, and two Big Buddy heaters with the green gas canisters, but I’m actually afraid to use any of those because of the need for fresh air/oxygen. That lets in the cold air. What is the BEST solution other than blankets and waking up to frozen buggers in a large camper? I don’t want to have to end up jumping out our bedroom window in the 5th wheeler.

Thank you for any suggestions or warnings 🙂


Tom H.
2 years ago

We use the heater in our electric fireplace, as long as temps do not get below freezing. Direct wired and won’t tip over. Heats 5th whl fine in all kinds of weather.

John Koenig
2 years ago

#1 solution to cold weather: PUT ON EXTRA LAYERS! Both of my air conditioners have heat pumps so, after additional clothing, that is my first “line of defense” when temps drop to around 50ºF (and generally use only one unit at a time due to noise). I use a 1500W ceramic heater on its’ 750W setting occasionally. That electric heater has a Safety Switch which shuts the unit off should the heater be knocked over. I use a small fan to move air around inside my rig. That evens out the temperature throughout the interior. Both my Smoke Alarm and Propane / CO Detector were professionally replaced late last year (when my Super-C was 5.5 years old). I’m always on the lookout for ways to improve the operation of my rig as I full time in it. In “regular years”, I put 10k~12k miles on my rig. The Covid19 Pandemic has put a HUGE dent in the driving I’ve done in 2020. In 2020, I’ll be WAY under 10k miles driven. I do NOT see a MAJOR improvement in conditions for 2021 🙁

Richard Dzialo
2 years ago

Actually had a circuit breaker in the motorhome go bad while the space heater was on. Twenty amp breaker. Could smell something was heating up and while trying to pinpoint the problem, the breaker popped. Appeard to be a loose connection on the breaker panel bus bar. Cleaned the contact surfaces and installed a new breaker. No issues since. Fortunately we were in the RV when it happened. One reason we don’t leave the space heater or the electric fireplace unattended.

2 years ago

Electric space heaters in an rv is a fire waiting to happen. I do not understand why people are to cheap to run the furnace. Propane is not that expensive. Stay safe.

2 years ago
Reply to  ron

I am not too cheap to run mine. I never use space heaters. Noisy and dangerous.

2 years ago

Mike, need to totally disagree with you that campgrounds support the use of CheapHeat on unmetered sites. The implication that it is “free” heat is a fallacy that I am surprised to hear you echo. The increased use of electricity in today’s RV’s creates a need for a much larger an proportionately costly campground electrical infrastructure. These costs are recovered either through metering or higher site costs. They are NOT free.

Tommy Molnar
2 years ago
Reply to  Mojo

Why would campgrounds not recoup their costs through metering? I thought that was the purpose of electric meters.

2 years ago
Reply to  Tommy Molnar

Tom, the comment referenced “unmetered” sites. Yes, metered sites would address increased electric utilization. That leaves the cost of substantially adequate and code compliant infrastructure costs – (50 amp 220 vac provides 3.33 times the power of a 30 amp 120 vac.) Do the 30 amp units pay for this ??

Tommy Molnar
2 years ago
Reply to  Mojo

Sorry Mojo, I misread your original post. We’re currently in a temporary long term situation here in Houston with a 30 amp hookup. We pay our electric bill separately and it amounts to just over $100/mo. Through June, July and August our a/c NEVER shut off!

Temps have dropped somewhat in the past week or so and we actually got to shut off the a/c and open the windows. I expect the electric bill to be less this month.

2 years ago

Another thing about space heaters that most people don’t think about is that they lose their heating efficiency over several years. All space heaters lose 10-15% of their wattage output within a couple of years of even light usage. I’ve measured the wattage of my 2 heaters over the years & They’ve dropped from 1500 watts when new, to 1300 watts after 2 years of just occasional use, & have dropped to under 1100 watts after about 4 years of light use. Not blowing out the dust that collects inside can also hurt the efficiency & cause a fire if it plugs the openings & causes heat build up.

Mike Sokol
2 years ago
Reply to  Fred

Fred, I’ve never observed this loss of wattage in a space heater as it aged. How exactly did you measure it? What voltage was the space heater connected to for each measurement? Remember, the wattage of a resistance heater will increase or decrease by the square of the voltage. That is, Voltage squared divided by Resistance = Watts. So even a small change in voltage will result in a large change in wattage. For example, if you reduce the voltage from 120 volts to down to 100 volts, a 1,500 watt heater will drop down to 1,041 watts of power output. Is that what you were observing?
However, dog hair (or other fuzzy things) stuck in the heater will indeed reduce air flow and increase internal heating with the possibility of a fire. As with many things electrical, not all of it is intuitive. You need to run the math to understand how it works.

2 years ago
Reply to  Mike Sokol

By the same token using your formula, if the resistance of the heater connections (and any cords/outlets) increases, then the wattage would also decrease. Sounds like a disaster waiting to happen.

2 years ago
Reply to  Fred

“Efficiency” – heat per watt – is wrong here. All electric heaters are 100% efficient …because all energy eventually becomes heat. If the plug oxidizes (or similar resistance changes to what’s drawn by the heater), whatever you draw will still be turned to heat.

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