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Old 12-08-2022, 02:47 PM   #1
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Electric Heater questions

Okay, so there is so much I don't really understand about electrical capacity and all that.

So, I was looking at electric heaters the other day as an option down the road, and the ones I was looking at have two power settings: 750W and 1500W, and they say they require 120V connection.

All the research I've done on skoolie wiring, people recommend a 110V system for appliances and electronics, which I thought was just the same as regular home wiring. And I was looking into a 3000W inverter to handle my fridge and convection microwave.

Based on that description, will the system I'm planning be able to handle that electric heater? Or will I need to do something differently than I thought?

It's probably a simple question, so I expect a lot of 'go learn about electricity' and 'no of course that won't work', but I'm here for it.

thanks

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Old 12-08-2022, 03:27 PM   #2
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if tyou use a portable electric heater like that 1500 watts which will kill your batteries in no time (assuming batteries since you mentioned inverter).. will give you about 5000 BTU of heat Max. or you can install a minisplit heat pumps.. which will give you 12000 BTU of heat at around 1000 watts (maybe a little more wattage if its under 20f outside)..


or a diesel heater which pulls maybe 100 watts and gives you about 17000 BTU of heat..
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Old 12-08-2022, 04:56 PM   #3
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Okay, but my question was whether or not the system I described could handle a heater with these specs.

Like, I just want to make sure I'm not going to blow myself up or overload my system or anything like that.
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Old 12-08-2022, 05:05 PM   #4
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Okay, but my question was whether or not the system I described could handle a heater with these specs.

Like, I just want to make sure I'm not going to blow myself up or overload my system or anything like that.
I think Christopher sort of answered that, given the info available...it will kill your batteries in short order. Backing up to just the inverter, yes...in theory a 3000W inverter should handle a 1500W load...but that's theory. In real world use, most inverters don't like resistive loads like a heater or stove and it would probably lead to failure earlier than you want.

Without knowing more about the battery bank capacity, we cannot really say whether your system can handle that heater.

EDIT to add clarification: My caution about the long-term use of resistive loads (like a heater, not a coffee pot) applies to my experience with HF inverters. I believe a quality LF inverter would fare better.
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Old 12-08-2022, 06:00 PM   #5
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Are you asking about the wiring or capacity? I slightly disagree with above replies. It really depends on many factors like the starting temp in your rig, if you're using a radiant barrier on your windows, etc. Electric heaters don't continuously pull power at certain rate. I use the Inergy Flex system (1500w inverter with 3000w surge) with an electric heater, and there's an initial surge in wattage, then it cycles down and eventually shuts off, rinse and repeat to maintain temp. My one battery will last all night. If its too cold for my heater to keep up with and just ran all night, yeah my battery would drain in an hour. It just depends on your battery bank and the other factors I mentioned.
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Old 12-08-2022, 06:52 PM   #6
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I think Christopher sort of answered that, given the info available...it will kill your batteries in short order. Backing up to just the inverter, yes...in theory a 3000W inverter should handle a 1500W load...but that's theory. In real world use, most inverters don't like resistive loads like a heater or stove and it would probably lead to failure earlier than you want.

Without knowing more about the battery bank capacity, we cannot really say whether your system can handle that heater.
System needs for a 1500 watt heater:

A bank of 2 100AH Lithium Ion batteries will feed an inverter 12.5 amps (sufficient for that 1500 watt heater) for a little over 12 hours continuous before needing to recharge the battery.

Ignoring battery charging needs, 4 100 Amp LiFePos will power that heater continuously.

Add in another 5 amps continuous for other loads, the heater could still run for about 9 hours, and a battery bank with 525 amps capacity would run the heater and that 5 amp load continuously.

You would need an inverter of at least 2500 watts to power such loads.

Hope this puts some meat on the bone....

(edit: none of this addresses the question of whether the 1500 watt heater will do the job of heating a bus)
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Old 12-08-2022, 07:07 PM   #7
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1500 watts is roughly 120 amps at 12 volts... that doesnt give very long continuous operation if its only 200AH
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Old 12-08-2022, 08:57 PM   #8
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(edit: none of this addresses the question of whether the 1500 watt heater will do the job of heating a bus)
If you're well-enough insulated and it's not too cold outside, it might do the job. I spent a night in my bus last week when it was 25°F outside and my 1500 watt heater on max kept the inside at 65°F. This was with 2" of XPS on ceiling, floor, sides, front, and back and all the windows, no thermal bridging from steel and very little thermal bridging from wood.

In a "typical" skoolie with a bunch of exposed windows and the entire uninsulated front cab incorporated into the living space, and with less thickness of insulation overall, I would bet just a space heater would struggle to keep a bus in the 40s when it was 25°F out.
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Old 12-08-2022, 10:01 PM   #9
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System needs for a 1500 watt heater:

A bank of 2 100AH Lithium Ion batteries will feed an inverter 12.5 amps (sufficient for that 1500 watt heater) for a little over 12 hours continuous before needing to recharge the battery.
I love you, my friend. But you made a common mistake. That 1500W heater uses 12.5 Amperes at 120 volts...but the inverter draws from the DC side. If it's a 12VDC system, that's 125 Amperes + some conversion loss.

Resistive heating is just hard to do in an off-grid rig. And this confusion is common. I recently had a customer who really wanted the resistive heated flooring mats installed and she said they "only draw 6 amps!" But that was 6 amps at 120 volts...converted to 12V DC that was going to suck 60 amps per hour from her batteries.
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Old 12-09-2022, 12:27 AM   #10
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while i agree with the others that resistive heat will kill your battery bank.... i don't see the need to run the heater off the battery.

my bookmobile had 3 - 240v electric heaters installed from the factory. they run off the generator just fine, or when im plugged into a 50a shore connection.

boondocking, i use a diesel heater.

electric for when you are parked and plugged in, is best though.
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Old 12-09-2022, 07:13 AM   #11
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while i agree with the others that resistive heat will kill your battery bank.... i don't see the need to run the heater off the battery.

my bookmobile had 3 - 240v electric heaters installed from the factory. they run off the generator just fine, or when im plugged into a 50a shore connection.

boondocking, i use a diesel heater.

electric for when you are parked and plugged in, is best though.
I mentrioned battery as he talked of a 3000 watt imnverter to run the heater which to me would indicate batteries / solar etc..



I do agree use electric heat off a shore power or generator if its available..
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Old 12-09-2022, 01:32 PM   #12
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I love you, my friend. But you made a common mistake. That 1500W heater uses 12.5 Amperes at 120 volts...but the inverter draws from the DC side. If it's a 12VDC system, that's 125 Amperes + some conversion loss.

Resistive heating is just hard to do in an off-grid rig. And this confusion is common. I recently had a customer who really wanted the resistive heated flooring mats installed and she said they "only draw 6 amps!" But that was 6 amps at 120 volts...converted to 12V DC that was going to suck 60 amps per hour from her batteries.
Sh!t! You are absolutely right, and a rookie mistake!

But not that tough to make, either! Let me highlight my error, since it's a good learning opportunity for anyone else trying to size their solar and house electrical systems.

Any appliance plugged into the inverter or a branch circuit off that inverter uses standard household electricity-120 volts, alternating current.

Most electrical devices we use in bus conversions, like pumps, diesel heaters, LED puck lights and the like us standard automotive electricity-12 volts, direct current.

For battery and wire sizing, there are two load calculations: first is all the 12 volt DC loads; and second is all the loads on the inverter-like this space heater-and you can't mix them when doing load calculations.

RV devices such as water pumps are 12 volt, and you can use their labeled amperage directly in your calculations for battery loads.

Any household appliance like a space heater that runs on 120 volts AC has a labeled amperage draw based on 120 volts, so you need to convert that load to its equivalent battery or 12 volt load (which is what I failed to do in the example I gave). The math is wicked simple-just multiply time ten.

So my corrected statement should be:

There is no practical way to run a 1500 watt space heater on a battery bank. It would draw 125 amps continuously, which would drain a 100 amp LiFePo battery down in less than an hour, never mind the sizeable wiring needed to drive that heater.

You could run that heater with a 2000 watt inverter, but you probably wouldn't want to build the battery bank needed to keep the heater on for more than an hour before it drains the batteries. Alternative heater solutions that would be much cheaper include RV propane heaters (which don't vent the combustion air into the bus) or better yet, a diesel heater or two.

Also, if you have access to shore power then you could run a space heater without trouble.


And to the OP, hopefully this discussion helps fill in some details around system sizing.

Thanks again Ross for the heads up on my error.
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Old 12-09-2022, 01:34 PM   #13
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110v vs 120v

Not sure if the 110v vs 120v was part of OP question, but without going way off into the weeds, think of them as the same. Some outlets are different according to amperage.

Electric heat is (as mentioned) hard to make. I think of my 1500W heater as a luxury item only to be used when parked up at bougie camps with electricity. Electric heat and Wifi usually come together

I went with wood stove for my main source of heat. Partly due to simplicity, partly because I run gas in my rig or I would have done a diesel heater (also as mentioned). But for me, electric heat was "out" from the start as a primary.

Giant solar farm and massive battery bank.... might be money/time spent better on alternate heat sources. Save the 1500w for when there is a cord to suck on.

Yeah, what "Rucker" said... his response came in while I was typing...
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Old 12-09-2022, 03:46 PM   #14
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Indeed, I use 120 volts in calculations as a convention. You might see 110 or even 115. For me it's just calculation convenience.

My inverter produces about 119 volts at the source.
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Old 12-09-2022, 04:08 PM   #15
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Yup, like CCC and Rucker said...there's no functional difference. In the old days, 110 volts was the standard...then it seemed to shift to 115...and in the 1980s the NEC changed the standard to 120 volts, with a tolerance of about 5% from that. So you'll see 110 volt or 120 volt systems and appliances used interchangeably. The same thing impacted 220, which is now 240 (since it's just a line-to-line voltage in a split phase panel).
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Old 12-10-2022, 07:45 AM   #16
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Yup, like CCC and Rucker said...there's no functional difference. In the old days, 110 volts was the standard...then it seemed to shift to 115...and in the 1980s the NEC changed the standard to 120 volts, with a tolerance of about 5% from that. So you'll see 110 volt or 120 volt systems and appliances used interchangeably. The same thing impacted 220, which is now 240 (since it's just a line-to-line voltage in a split phase panel).
Haha, thank you for answering my actual question!

Yeah, I know that electric heat is not the most efficient way to heat a bus, especially when I plan on keeping as many of the original windows as I can—though I am planning on walling off the front cab so it isn't integrated into the living space.

My First Choice of heating would be a wood-stove, but I'm concerned about the logistics and realities of trying to get my bus insured. So, I'll probably be opting instead for a couple diesel heaters as my go-to heat source. They'll get the job done, but I gotta say I'm disappointed by their lack of ambiance.

I considered for a little bit the possibility of a propane fireplace, or even looking for some kind of indoor propane firepit. My cooktop will be running on propane, so I didn't think this was outside the realm of possibility. But reading up on those it's pretty clear that ventilation would be an issue to avoid carbon monoxide buildup.

And so that brought me to these electric fireplaces and prompted my question. I like the look of them, and they're pretty compact. I could see theoretically that it could be something I could set up and plug in occasionally, as a 'luxury' option as CrowCreekCabin put it, when I have ample battery power or am plugged in to shore power. I don't know yet how often either of those will happen, so I see I probably shouldn't count on this as my primary heat source.

FWIW, I'm still in the early stages of designing my electrical system, trying to size it out based on what I think my needs will be. I know I have about 2300W of solar panels, but I don't have my batteries yet. And I know that 2300W won't be constant, I have done some research on this.

So, I don't know - I still kind of want one of these electric fireplaces just for the lightshow - the super-low-power option - but not to run it as a heater. Having it as another backup heating option wouldn't be the worst thing either, I suppose.
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Old 12-10-2022, 07:51 AM   #17
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Old 12-10-2022, 07:53 AM   #18
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Are you asking about the wiring or capacity?
Yeah, I was asking primarily about the wiring I guess. Making sure that if I plug this 120v appliance into (what I understand would be) a 110v system, that nothing bad will happen on either end of that equation. Sounds like both of these labels are just kind of shorthand for 'residential AC power'.
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Old 12-10-2022, 08:06 AM   #19
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We started out with a wood stove and planned on using a propane Buddy heater and 1500w electric space heater for supplemental heat when needed. The wood stove is one of those tiny ones and while it does put out some good heat, its a bit finicky and needs to be reloaded every 45 minutes or so. In reality, its supplemental heat. The electric space heater didn't do much good (the few times we did use it) and we weren't really ever on shore power so we donated it to Goodwill somewhere around Rapid City, SD. The Buddy heater worked OK but the prospect of not waking up due to CO was always in back of mind. We'd cordon off the back of the bus, with a curtain, where the bedroom is at night...less space to have to heat.
Once the temps started getting into the single digits in Moab, it was clear that the wood stove and the Buddy heater wouldn't cut it. We didn't want to pack up and move south just because of some cold weather. So we installed a diesel heater. That was a game changer. We could comfortably do cold weather and sleep through the night without needing to feed the stove. We spent a pretty cold winter in the mountains of western NC and the diesel heater allowed that to happen comfortably. The stove is great for ambiance and taking the chill off but when we need no-fuss heat then its diesel all the way.
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Old 12-10-2022, 02:39 PM   #20
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So, I don't know - I still kind of want one of these electric fireplaces just for the lightshow - the super-low-power option - but not to run it as a heater. Having it as another backup heating option wouldn't be the worst thing either, I suppose.
This is exactly what I am doing. I have an electric "fireplace" with the realistic looking fake fire and logs, the whole unit is very nice looking but in the end as a heater its just a space heater with a pretty facade. But I'm allergic to smoke and also don't want issues with insurance. The fake fireplace can do the fire effect without the heater running, its one of the settings. So you can use the diesel heater for actual heat and your fake fireplace for ambience. The unit takes up a lot of space but for me its one of my favorite things and worth it. Everybody has those items they sacrifice space and weight for and this is one of mine. I also like the idea of redundant options. I even kept my bus's original heaters. I have a 12v electric blanket and I'm installing a diesel heater. If I'm plugged into shore I can use my fireplace.
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