Max wattage for space heater when plugged into shore power?

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Max wattage for space heater when plugged into shore power?

August 22, 2019, 10:17:22 am

I'm looking at getting a space heater for the RV. However, what's the safest max wattage I should get for the rig? I have an 89 Lazy Daze Twin King.

Re: Max wattage for space heater when plugged into shore power?

Reply #1 – August 22, 2019, 11:50:50 am

We have used a variety of 1500 W heaters over the decades, and with our '83 had issues with the inside AND post circuit breakers tripping. Mostly just used the lower heat setting without incident. Never clear if the issue was with the heater or old circuit breakers or ?. Anyway, never had the issue with the roof air.

With our '04 model, we have a roof air heat strip and a better, quiet portable heater that have not had any problems. Vornado VH200.

Steve

Re: Max wattage for space heater when plugged into shore power?

Reply #2 – August 22, 2019, 11:58:18 am

To sidetrack this thread a bit, the roof air heat strip is interesting to me, something that the 80's models did not have. How do they work? Do you need to be hooked up to shore power for them to work?

Re: Max wattage for space heater when plugged into shore power?

Reply #3 – August 22, 2019, 12:00:36 pm

If the plugs are on a 15AMP breaker, you should be able to use a 1500W without problem unless you're simultaneously running another energy hog (coffee maker, hair dryer).

In reality, that assumes that the RV wiring/breaker are performing as designed AND the campground wiring is up to the task. Campground electricity varies widely.

I would go for something with multiple settings (for the heating elements, not just the fan) and realize that it might be trial and error at some campgrounds.

Heat strips are just a heating element that can be added on to many RV A/C units. They use shore power. Electricity flows through a resistor and gets hot; the A/C fan is used to blow air and distribute the heat.

Rich
'03 MB in NC

Re: Max wattage for space heater when plugged into shore power?

Reply #4 – August 22, 2019, 12:01:49 pm

Quote from: jacobjm - August 22, 2019, 10:17:22 am

I'm looking at getting a space heater for the RV. However, what's the safest max wattage I should get for the rig? I have an 89 Lazy Daze Twin King.

Jacob, most small space heaters have 2 settings, 1500w and 750w. Some have 3, with another setting in between. Anything more powerful than 1500w will probably pull more amps than you need or can support with a 15 amp outlet.

Chris

Re: Max wattage for space heater when plugged into shore power?

Reply #5 – August 22, 2019, 12:04:48 pm

Quote from: HiLola - August 22, 2019, 11:58:18 am

To sidetrack this thread a bit, the roof air heat strip is interesting to me, something that the 80's models did not have. How do they work? Do you need to be hooked up to shore power for them to work?

heat strips, how do they work?

Yes, hooked up unless you are using genset or have huge solar array.

Chris

Re: Max wattage for space heater when plugged into shore power?

Reply #6 – August 22, 2019, 01:00:01 pm

Then as long as your breakers are good (flip when they are supposed to), and you have a "if tips over - turns it self off" space heater, you are safe. But as others interpreted, I think you are asking do you need to be concerned about if it will flip a breaker when overloaded (causing the trouble of resetting everything and potentially harming electronics with the sudden loss of power).

I would add to what Rich said, that you not only have to be aware of what you are using on that one breaker, but also for the entire RV.

Older LDs did not have a microwave on a separate breaker. So a spaceheater plus hog of a computer (e.g. big screen all in one) and the microwave would flip that outlet breaker quickly, even if the space heater was running on low watts (been there, done that).
If you have a newer LD which has a dedicated microwave breaker, you could still run too many things and overload the main 30 amp breaker.

So it might be a matter of turn the heater off before you turn on ..... if you are using several high energy use devices at the same time.

Jane

Re: Max wattage for space heater when plugged into shore power?

Reply #7 – August 22, 2019, 01:12:07 pm

Here is something to consider:

A 1500 W electric heater is 100% efficient, and is equivalent to about 5100 Btu/hr. The propane furnace is about 20,000 Btu/hr, and maybe 60% efficient. That is still 12,000 Btu/hr of heat output, which will outperform any electric heater or heat strip if the goal is to combat extreme cold or heat up the interior quickly. If an alternative to electric heat, I assume you have shorepower to also power the furnace. A pound of propane contains 21,600 Btus, to gauge propane usage.

Steve

Re: Max wattage for space heater when plugged into shore power?

Reply #8 – August 22, 2019, 01:22:02 pm

I didn't get the heat strip in the A/C, maybe it was an option in 1999 that I didn't know about. I've never missed it. The volume level on the A/C fan, even set on the low speed, is too high for me. A small box heater in the 800 watt range works for me. I'm sure it is no longer available, but it has a thermostat I can set for about 55 degrees. It keeps the RV comfortable enough, and uses electricity from a 'full' hookup' that I'm paying for anyway. Any colder and I have three cats vying for position all night, trying to stay warm. (You'd think they didn't have fur coats!) RonB

Actually found it on Ebay! Not new of course. Tatung Heat Devil 1500w Ceramic Disk Compact Portable Electric Heater...

Re: Max wattage for space heater when plugged into shore power?

Reply #9 – August 22, 2019, 03:18:00 pm

Some comments:

1. As Ron pointed out, the air conditioner heat strip option is noisy. Also, it blows hot air from a central location on the ceiling, which is probably the least desirable way to heat a room. You want hot air coming up from below, not forming a layer above. This option can be useful when you have shore power and want to heat things up fast, because it's on a separate circuit from all the other outlets (except the microwave's outlet), so you can use it along with an electric space heater or two without tripping a breaker. But in my 8 years of all-weather camping in my LD, I rarely needed to do that.

2. About electric space heaters: two of them running on low will do a better job of evenly heating your coach than one of them on high. If possible, get heaters with three heat settings (600/900/1,500 watts). That way you can run two of them on the 600 W setting at the same time, and still have power left over for a few other things. Two space heaters at 750 watts each will bring your outlet circuit close to its limit. If the fridge, which draws about 350 watts when running on 120 VAC, turns on at the same time, you'll probably trip a breaker.

3. Fancy "ceramic" heaters usually have small heating elements with narrow air passages that clog up rapidly with dust and pet hair. This reduces heating efficiency and can pose a risk of fire. In my experience, the best small heaters are the cheap ones ($16-20) with open coils of resistance wire. They are slower to clog, and much easier to clean.

Re: Max wattage for space heater when plugged into shore power?

Reply #10 – August 22, 2019, 06:59:09 pm

Jacob, a 1500 watt heater using 120 volts draws, in theory, 12.5 amps. If you have a TV or a computer on, drawing 3 amps, and you plug in a 1500 watt load, you are overloading a 15 amp breaker. If you plug in a 1500 watt heater on the LD common line, you can't plug anything else in. Even if you have nothing else plugged in on that circuit, you can't run another heavy draw such as the microwave simultaneously, even though it is on a different breaker.

Ken F in WY

Re: Max wattage for space heater when plugged into shore power?

Reply #11 – August 22, 2019, 10:07:04 pm

Cycle the heater on and off when using higher settings. Other wise, it could melt the plug to the connector at the pedestal if it runs continuously for mucho time. Don’t ask me how I know!

Ron

Re: Max wattage for space heater when plugged into shore power?

Reply #12 – August 23, 2019, 02:17:59 am

Ron... Ok, so you had a space heater and had it plugged into an LD outlet and it melted the LD plug into the pedestal (shore power)?
Or was the space heater plugged directly into the pedestal (along side the LD plug).

That is a new one to me. I would guess something was not working right (plug issue, easy to have those prongs wiggle a little), pedestal problem, breakers not working, something. Maybe even sunlight on the plug making it extra hot (ok, I might be stretching a little here).

I have had a plug melt when plugging it in (luckily our main LD breaker was off). It was because there was a little wiggle in the plug. I learned the lesson to turn the pedestal breakers off (and we take the extra step of turning the LD off) then plug/unplug, then burn the pedestal breakers on and last we turn the LD breakers back on.

Your expeience shows us that we should all be checking our electrical items regularly (connections, cords, plugs, etc.).

Jane

Re: Max wattage for space heater when plugged into shore power?

Reply #13 – August 23, 2019, 08:27:46 pm

Quote from: Kenneth Fears - August 22, 2019, 06:59:09 pm

Jacob, a 1500 watt heater using 120 volts draws, in theory, 12.5 amps. If you have a TV or a computer on, drawing 3 amps, and you plug in a 1500 watt load, you are overloading a 15 amp breaker. If you plug in a 1500 watt heater on the LD common line, you can't plug anything else in. Even if you have nothing else plugged in on that circuit, you can't run another heavy draw such as the microwave simultaneously, even though it is on a different breaker.

Ken F in WY

Ken,
Can you clarify why you can't run another heavy draw (on a separate circuit) when you have a 1500W (12.5 amp) draw on the 15 amp common line? My 31' has 20 amp 120v circuit for the microwave and coffee maker (removed by previous owner) so I wold think I could use that outlet as another 120v source.
I would think that there's 24 total amps @120 volts available considering the 30 amp main. Or, am I missing the load for the convertor/ battery charger? something else?
Thanks!
Ron

Re: Max wattage for space heater when plugged into shore power?

Reply #14 – August 23, 2019, 08:33:52 pm

"Cycle the heater on and off when using higher settings. Other wise, it could melt the plug to the connector at the pedestal if it runs continuously for mucho time."

If a 30A shore power plug melted, the problem was not a 12.5A heater. Your shore power cord, plug, and the outlet at the pedestal are all rated for 30A continuous duty. The problem you experienced was most likely due to either poor contact at the pedestal socket--fairly common in sockets that sit outdoors in all weather for years without maintenance--or a shore power plug with failing internal wiring.

There's no need to cycle your heater on and off. There is a need, as Jane pointed out, to check the cord, plug, and pedestal socket. While you can't get inside the socket to clean its corroded contacts, you can clean your shore power plug's prongs with sandpaper or Scotchbrite until they're shiny and bright, then spray them with contact cleaner before plugging in.

Re: Max wattage for space heater when plugged into shore power?

Reply #15 – August 23, 2019, 10:33:01 pm

Ron, to clarify, the load carried by the breaker in the pedestal includes everything you have running. If you are running a 1500 watt heater, using 12.5 amps, and you run a 1500 watt microwave at 12.5 amps, plus your refrigerator at 3 amps, that is a total of 28 amps. Add anything else, and you can do in the pedestal breaker. Most of us have stuff drawing on the 120 volt system that we don't think about. These can include the refrigerator, the converter to put back the amps you are drawing for the 12 volt stuff from your battery bank, in my case the computer, TV, DVR, and at night my CPAP machine. Add ALL of those amps together, add in the amps for a heater, and if you add another heavy draw, such as a microwave, a toaster oven, a coffee maker, a hair dryer, etc., and you may be overloading the pedestal. The individual breakers in your panel are there to protect ONLY the circuit wiring that is "downstream" from THAT breaker. Everything - 120 volt and 12 volt - in your RV is "downstream" from your pedestal and shore connection, and it all counts.

If I add up every breaker in my system, I am well above 100 amps. Any one of those can safely go to a load near its rating without overloading that circuit. If I ran all of them at the same time, it does not matter if each was within its rating. The pedestal breaker would get fried.

Does that clarify why you have to watch out for having two heavy loads operating at the same time, even though they are on separate circuits? You need to keep the total from everything below 30 amps.

Ken F in WY

Re: Max wattage for space heater when plugged into shore power?

Reply #16 – August 24, 2019, 09:56:20 am

"There's no need to cycle your heater on and off. There is a need, as Jane pointed out, to check the cord, plug, and pedestal socket. While you can't get inside the socket to clean its corroded contacts, you can clean your shore power plug's prongs with sandpaper or Scotchbrite until they're shiny and bright, then spray them with contact cleaner before plugging in."

I'd add to this two things. First, one should have to exert some force to plug the shore power plug into the pedestal socket. If the plug sags when plugged in, or feels loose, it does not have a proper electrical connection (worn socket). Under a load, this will likely cause the plug to get hot and degrade it. Second, on molded shore power plugs, the individual prongs should not 'wiggle' in the plug. If they do, it indicates they have been hot at some point, and at the least should be monitored closely for further signs of deterioration.

Bill

Re: Max wattage for space heater when plugged into shore power?

Reply #17 – August 24, 2019, 10:19:51 am

On a single phase 112 RMS AC voltage at 30 amps you can pull about 3300 watts before hitting max load.

Watts to Amps / Amps to Watts Electrical Conversion Calculator

glen

Re: Max wattage for space heater when plugged into shore power?

Reply #18 – August 24, 2019, 12:10:39 pm

Knowing how much amperage is actually being used is another great feature of a hardwired surge protecter.
The Progressive Industries' EMS-HW30C remote-mounted fob shows the amperage used, along with voltage and any error codes, indicating an improperly wired pedestal.
It's very handy in determining what devices can be run at one time without popping the 30-amp breaker.
Progressive Industries EMS-HW30C

Larry

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