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Is there a practical or rule-related reason that electric baseboard heaters in the US max out at around 2500W? It's common to have them on a dedicated 240V 20A breaker so it seems obvious to make 3840W a common size, but nobody does.

I wrote to a couple of manufacturers and got meaningless replies with no explanation.

I'm wondering if there is a reason driven by some code or practical consideration. There are plenty of other appliances designed to work at circuit capacity including garage heaters designed for 20A and 30A circuits at 80%, but not baseboard ones.

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  • Maybe they cannot depend people will not use them on 240v 15 amp circuits. Or in insulated rooms it is usually enough power/heat output.
    – crip659
    Commented Oct 13, 2023 at 15:13
  • @crip659 hmmm yes the available ones can all be installed on a 15A circuit. So there's something in your point there. Though not really an explanation. Yes you want to sell versatile products that can be installed on #14 cable if possible. But that doesn't go far enough to explain why nobody makes any product more powerful than that. Similarly, in rooms that don't need more power, you don't need more power ... but that also doesn't really explain it.
    – jay613
    Commented Oct 13, 2023 at 15:30

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Electric heat is cheap to install but expensive to run. You also don't actually need a huge amount of it for small rooms. In fact, a quick search finds that below the 2,500W level there are 1,500W and even 500W baseboard heaters. Which means for a really small room (e.g., a typical small old bathroom), you size it appropriately and keep the door closed most of the time. And if you have larger rooms than 2,500W can handle, you use multiple units.

The house I grew up in had electric baseboard heating because it was built at a time when there was a moratorium on new gas hookups and effective heat pumps were not yet available. It was, relatively speaking, horrible. But in reality, except for the basement it really wasn't that bad. Most rooms had one baseboard unit, but some rooms had 2 or more - and that worked OK except on really cold days.

There is actually an advantage to smaller units running "most of the time" vs. larger units "some of the time" - peak demand. Consider if you have a large house that might typically be sized for a 100k BTU gas furnace. 100k BTU/hr = 29.3 kW. At 240V that's 122A - more than half of a 200A supply, and with a continuous derate it's even worse - 152A! But a gas furnace doesn't normally run continuously, except on a really cold day or starting with a cold house. Let's say a 50% cycle is the expected normal maximum. That's an average of 50k BTU, which is equivalent to 14.6kW, which is 61A or 76A continuous. That is actually manageable on a 200A service with everything else, as long as you don't have tankless electric hot water or a huge EV charger (neither of which was a thing when I was growing up).

I would venture to say that most baseboard heating today is used as either supplemental heating in specific rooms (bathroom in a warehouse or basement or garage that isn't otherwise heated very well, shed, garage, addition where extending ductwork wasn't practical, etc.) where often a single unit 2,500W is actually sufficient, or is used for heating an entire house because natural gas is not available and heat pumps are "too expensive". Heat pumps are not truly too expensive when you look at total cost of ownership. But if you are, for example, a landlord and you are not paying the electricity bill then you are not actually looking at total cost of ownership - you are looking at equipment and installation cost and not considering the running cost. And if you are, for whatever reason, putting in baseboard electric heat for an entire house then oversizing it leads to higher peak demand which, if it is high enough, means increasing the utility service size and that can get expensive. So continuous "just enough" heating actually makes sense in that context.

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    So ya, my situation exactly. A bonus room over the garage with a three foot baseboard, I want to replace it with a six foot one and I figured I'd buy the most powerful one I can. You're saying a 3840 watt one would have an unnecessarily low duty cycle and high impact on my panel load. (I have the capacity but that's beside the point). And if I had a bigger room I would want to spread the heat with multiple six foot units not concentrate it. A 30A garage heater spreads it with a fan, with baseboards you need more of them not stronger ones. Makes sense.
    – jay613
    Commented Oct 13, 2023 at 16:04
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My suspicion is it is market driven. My experience is baseboard heater wattage is pretty much a constant watts per foot, making a 3800 watt heater length impractical for most locations.

I would note I have found it common to have two heaters per circuit, two heaters up to 1500 watts on a 20A circuit sometimes feeding multiple rooms, or two heaters up to 2500 watt each on a 30A circuit.

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  • Ya, I was thinking about watts per foot. I'm wondering if it's limited because they rely on convection and more feet gets you a lot more airflow and better distribution. Maybe a too-powerful heater will create concentrated heat that cannot be distributed well by any baseboard heater using convection. If you WANT the concentration, you probably want a radiant heater pointed at you, not a convector. And you can have a 6kW ceiling heater because it uses a fan to distribute the heat.
    – jay613
    Commented Oct 13, 2023 at 17:42

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