Electric heating/wiring question

[frazwood]

I am looking to add two electric wall heaters to a lake cabin. The wall heaters that I have picked out are 2000W/240V/8.3 amp heaters.

Ideally, I'd like to wire two of these heaters onto a single circuit in series because my electric panel is running out of space. Is that a ridiculous idea?

My thought that is that I could get a 30-amp, dual-pole breaker and 10-gauge wire and I would have plenty of capacity to safely to handle three of these heaters (adding a third heater in the future is a legitimate possibility).

Thanks for your input.

[ncesi]

You can legally put 3750 watts on one 20 amp circuit. You are on the right track run #10 wire and put it on a 25 or 30 amp breaker and you are good to go. To add the third heater of that size would not be to code as another 2000 watt heater would exceed the max allowed. If a piece of heating equipment can run for more than 4 hours and these could the code requires us to up size the wiring and breaker ratings by 25% more. 2000 watts + 2000 watts = 4000 watts divided by 240 volts = 16.67 amps times 1.25 = 20.84 amps so a 25 or 30 amp wiring method is required. Hope this helps you out.

[Tom7227]

I have been checking on baseboard heat myself. You can chose a wall mounted thermostat or ones that are right on the units. Figure out what you want as the wiring is a bit different for each. I think they are add on's and have to be bought seperatly.

[frazwood]

You can legally put 3750 watts on one 20 amp circuit. You are on the right track run #10 wire and put it on a 25 or 30 amp breaker and you are good to go. To add the third heater of that size would not be to code as another 2000 watt heater would exceed the max allowed. If a piece of heating equipment can run for more than 4 hours and these could the code requires us to up size the wiring and breaker ratings by 25% more. 2000 watts + 2000 watts = 4000 watts divided by 240 volts = 16.67 amps times 1.25 = 20.84 amps so a 25 or 30 amp wiring method is required. Hope this helps you out.

Thanks. This helps a ton. I have a good idea of what I am doing, but I wasn't sure. In this case, I didn't know about the need to accommodate an additional 25%.

[frazwood]

I have been checking on baseboard heat myself. You can chose a wall mounted thermostat or ones that are right on the units. Figure out what you want as the wiring is a bit different for each. I think they are add on's and have to be bought seperatly.

This wall heater unit that I am looking at is a bit different than a baseboard heating unit.

The baseboard units, as far as I can tell, are designed to have multiple units in series (for example, so you can place a unit under each window), all of which can be controlled by a separate thermostat located on a different wall.

The wall heaters that I am considering seem to be more powerful and include a fan. This is perfect for our application where we show up relatively late on a Friday night to a cold house with little kids who need to get to sleep fairly quickly. So, at this point, I need a better heating system for the kids' bedroom and I would like better heating for the second bedroom (where my wife and I sleep).

[ncesi]

Once again right on. The fan units will heat the space faster but cost more. The baseboards will take a bit longer but are more economical. For what you are asking and relaying the blower units will do the job better. the fans do make some noise but no more than a furnace fan.

[SkunkedAgain]

I would think that you could still go the easy route of using regular baseboard heaters and just put a small $10 fan in the kids' room to push the air around.

I take my 3yr old to our remote cabin all winter long. It takes hours to heat up our A-frame with the wood stove, plus or minus a few hours depending on outside temps. I put a heated blanket on her twin bed. She perks up for what I call "party hour" right after we get there so the blanket has enough time to heat up the bed. You're trying to heat up the whole room when you could save considerable time and money focusing on the bed. You could also get heated mattress pads.

In my basement renovation, I put in a 30amp subpanel (4 gauge from the main to sub) and ran a line out to the wall thermostat and then three baseboard heaters. It works great and nothing else is on the circuit.

[LightningBG]

Ideally, I'd like to wire two of these heaters onto a single circuit in series because my electric panel is running out of space. Is that a ridiculous idea?

I think we all know what you are trying to get at, but just to be clear... You will be wiring these heaters in "parallel" on a single circuit, not in "series". Just wanted to clear that up for when you start looking at wiring diagrams, etc, or talking with suppliers or contractors.

[BobT]

You can legally put 3750 watts on one 20 amp circuit. You are on the right track run #10 wire and put it on a 25 or 30 amp breaker and you are good to go. To add the third heater of that size would not be to code as another 2000 watt heater would exceed the max allowed. If a piece of heating equipment can run for more than 4 hours and these could the code requires us to up size the wiring and breaker ratings by 25% more. 2000 watts + 2000 watts = 4000 watts divided by 240 volts = 16.67 amps times 1.25 = 20.84 amps so a 25 or 30 amp wiring method is required. Hope this helps you out.

Where do you come up with the 3750W max? I'm not familiar with this limitation. 20A @ 240v = 4800W less any derating for circuit run length.

[frazwood]

Where do you come up with the 3750W max? I'm not familiar with this limitation. 20A @ 240v = 4800W less any derating for circuit run length.

I'll try to answer the question, now that I have been taught something new.

yes: 20A @ 240 V = 4800 W.

But, for a heater that might run for four consecutive hours, you need an extra 25% capacity. So, 4800 W divided by 1.25 = 3840 W. I'm guessing that the 3750W is approximate.

[BobT]

I'll try to answer the question, now that I have been taught something new.

yes: 20A @ 240 V = 4800 W.

But, for a heater that might run for four consecutive hours, you need an extra 25% capacity. So, 4800 W divided by 1.25 = 3840 W. I'm guessing that the 3750W is approximate.

This is new to me. Don't know where the duty cycle comes into play. Please cite the NEC code that applies.

Thanks.

Edit: Just so you know why I'm asking these questions. I installed baseboard heating throughout my home. Heating circuits are a purely resistive load. I do not recall reading anything in the code that required de-rating as you described above and none of my work was cited for code violation and I know some of those circuits exceed 3750W on 20A circuits with 12awg. Trying to figure out if this was a recent change in the law or something.

[Sorgy]

Frazewood,

I believe that we have one of the heaters you are asking about. So far I have not been very impressed with the heater. I have now had one of the two elements quit heating on 2 different occasions. For our place I am seriosly considering adding a Propane - fireplace/Franklin type stove in the corner of our bunkhouse.

We have a Base board heater in the bedroom and the double unit wired in the main room. I am not shure where to go from here on replacing the wall unit again(first one was under waranty).

We have a really well insulated bunkhouse that the heat is turned off on all winter. So it only runs in the spring and fall.

I would look at baseboard heaters again instead of the in wall units.

Steve

[frazwood]

This is new to me. Don't know where the duty cycle comes into play. Please cite the NEC code that applies.

Thanks.

Edit: Just so you know why I'm asking these questions. I installed baseboard heating throughout my home. Heating circuits are a purely resistive load. I do not recall reading anything in the code that required de-rating as you described above and none of my work was cited for code violation and I know some of those circuits exceed 3750W on 20A circuits with 12awg. Trying to figure out if this was a recent change in the law or something.

I don't know anything specific about NEC code. I am just following the advice given above. I've seen it elsewhere too. For example, and this is hardly official, look at step#9 of this:

Heater Wiring

And, again, I don't know what's code and what isn't here. I do know that inspectors miss things on occasion (because we're all human, right?). If you are worried about it, you could call the inspector and ask. It could also be a situation in which it is "recommend but not required." At this stage, for me, I'm going to follow this because it's easy for me to follow, doesn't cost much extra (if at all), and it definitely won't hurt.

[frazwood]

Thanks for the input. There are several factors going into this decision, but we're going to try the wall heaters. There are several different manufacturers, so it's possible that we are talking different heaters. I'd definitely double check user comments for the ones that I was considering.

[ncesi]

Article 424.3 B States Fixed electric space Heating equipment shall be considered a continuous load.

Article 210.19 A 1 a, Where a branch circuit supplies continuous loads or any combination of continuous and non continuous loads, the maximum branch circuit conductor size shall have an allowable ampacity not less than the non continuous loads plus 125 percent of the continuous load.

Article 100 Definitions, Continuous load, A Load where the maximum current is expected to continue for 3 hours or more.

20 amps x 240 volts = 4800 watts. 4800 watts divided by 1.25 = 3840 watts max on any branch circuit for fixed electric space heating. 3840 divided by 240 volts = 16 amps. We are required to only load a overcurrent device to 80% of it rating, 20 amp breaker x 80% = 16 amps.

We use the rule of thumb of 3750 as that matched the standard sizes of baseboard heaters and blower heaters. it is normally about 250 watts per foot. 2' = 500 watts, 4' is 1000 watts, 6' is 1500 watts and a 8' is 2000 watts.

I hope this clears the questions up.

[delcecchi]

Thanks. I didn't want to register or anything to see the NEC.

[Smoker]

I just went through continuing ed today and that is one thing that was covered. Kabakonacrazy is right

[BobT]

Interesting. I wonder how my inspector missed that on both the preliminary and final inspection of 8 separate heating circuits. I'll have to double check the loads I have on them. Maybe I didn't load them as much as I thought?

[ncesi]

BobT. In a normal house heated all the time this would be way less of an issue as all the heaters never run continuously or at the same time so most likely one never sees the full load for a prolonged period. The inspectors would hard pressed on each job to track each circuit and add up how much you have on each, they simply just do not have time as it would take hours to figure out once the home is finished. they could tell easier on the roughin but at that time they have no way of knowing what heaters will be installed in the end. If you have 4000 watts on a circuit and have not had any nuisance breaker tripping issues then doo not sweat it. If you had more than that you would already know.

[Sorgy]

The heater I used was bought at the "Save Big Money" store. It was the only wall mount heater that they carried and it mounted inside the wall with a grate or cover with the knob for temp on the front.

[BobT]

BobT. In a normal house heated all the time this would be way less of an issue as all the heaters never run continuously or at the same time so most likely one never sees the full load for a prolonged period. The inspectors would hard pressed on each job to track each circuit and add up how much you have on each, they simply just do not have time as it would take hours to figure out once the home is finished. they could tell easier on the roughin but at that time they have no way of knowing what heaters will be installed in the end. If you have 4000 watts on a circuit and have not had any nuisance breaker tripping issues then doo not sweat it. If you had more than that you would already know.

Good point! I did this work almost 15 years ago so my memory isn't all that trustworthy. After reading what you wrote here, I now recall that I figured the system was not a continuous duty cycle and that is why I was able to do it the way I did. Thanks. It's fun getting older.

[ncesi]

I am with you on that one. I am getting older as well but this just happen to be my profession. I grew up in the electrical contracting business working for my father and now run a company of my own. Goo d luck and have an excellent weekend!!

[Surface Tension]

I wouldn't use that style heater. When the fan fails and it will you have a big problem. You have a heating element relying on a fan to cool it.

Being mounted inside the wall makes matters worse. I just don't like them at all.

I'd mount the electric baseboard. It'll heat the room just as well or better because you can mount them where they belong and with the correct wattage for the room. If you can afford only one circuit then up the wire size and the appropriate breaker to protect the wire.

[frazwood]

The heater I used was bought at the "Save Big Money" store. It was the only wall mount heater that they carried and it mounted inside the wall with a grate or cover with the knob for temp on the front.

My wife does not allow me to shop at that store. :-P

I've read the online reviews for the model that I want and they all seem good. Of course, online reviews are biased because they tend to include: (1) people who got a bad model, or (2) people who wrote the review when the product is new.... it'd be really great to get reviews from people two years post-purchase.

[frazwood]

Interesting. I wonder how my inspector missed that on both the preliminary and final inspection of 8 separate heating circuits. I'll have to double check the loads I have on them. Maybe I didn't load them as much as I thought?

The other thing to remember is that the electric code is incredibly conservative. The idea behind the code is to never have a fire, ever, no matter what stupid idea the home owner tries (and this is not a complaint about the code -- I like this, in fact).

There are almost always two safety measures (or more). In this case, the circuit would be oversized by 25% for safety and then there is also a breaker there for safety.