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My house is mostly steam heat, but prior owners put on a small addition and also turned an upstairs closet into a bathroom. These new rooms have electric baseboard heat.

Heaters work fine, but thermostats are crummy. Especially in the bathroom. It only functions as an on off switch at the moment so I want to replace that one.

I'm handy enough not to kill myself swapping it out, but not well enough informed to pick out a replacement.

The bathroom is heated by a single heater with a label indicating:

750W @208VAC

1000W @240VAC

The existing Thermostat has a label indicating:

125/250/277 VAC

22A Double pole

Attached are pictures of the the spec label on the heater (the bathroom only has one of the smaller baseboard units) and the existing thermostat.

I cant find these exact specs in a replacement thermostat. Specifically I'm finding sats rated for 240v, 3600W, and 15A So my question is: Can I use any line volt stat rated for greater than or equal to 1000W and 240V or are there other considerations? For a single 1000W heater, the existing 22A stat seems overkill, no?

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Any thermostat rated at or above the heater ratings should work fine. 3600W is a good number because that is 15A @ 240V, which is also a common breaker size. My guess is that the original installer used the same thermostats everywhere, costing a little more but minimizing the number of inventory items. 3600W/15A also allows you to upgrade a bit in the future without replacing the thermostat.

  • Keep in mind that heaters need a 125% derate, so a 15A breaker can only power 12A of heater. – Harper Nov 20 '18 at 17:09
  • I suspected that might be the case, but didn't know for sure. But even at that, 1500W (the larger of the 2 existing heaters, 6A) is well within range, and a total could be up to 12A = 2,880 - much larger than the existing heaters. Plus we're only guessing that the existing wiring & breakers are 15A as a minimum. For all we know, the wiring & breaker might be rated for 20A. – manassehkatz Nov 20 '18 at 17:10
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    When sizing a breaker for a heater or any continuous load, take its amps and multiply by 125%. You need that much breaker for it. For instance say you have a 12A heater and a 3A bathroom fan on a timer, which is not a continuous load. You cannot put both on a 15A breaker. You compute 125% of 12A which is 15A, add the 3A, total 18A - that fits with room to spare on a 20A breaker. – Harper Nov 21 '18 at 19:42
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    @Zipper1365 most people actually do it backwards because the math is easier: if you pretend all loads are continuous, you work backwards and multiply the breaker by 80%, e.g. A 15A breaker can support 12A of continuous load or heater. A 20A breaker would support 16A, which again would fit the 12A heater + 3A fan in the above example. (This ignores the fact that the fan is not a continous load, but that makes little difference, and it is simpler to think about.) – Harper Nov 21 '18 at 19:45
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    @Zipper1365 sounds right to me, since the thermostat is designed specifically for loads that are always rated as continuous loads. Indeed, a magic number that is 80% of a common breaker rating is a good indication. – Harper Nov 21 '18 at 21:05
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There‘s no such thing as a cheaper, smaller thermostat

Because of diminishing returns, there just isn't much manufacturing cost savings to be had on a 10A thermostat vs. a 20A or 30A thermostat. As such, there's a minimum size they'll make. Your needs will be below that minimum.

What's more, even 30A thermostats are cheeeep. When a big one costs $12, there's no point making a little one for $11.

Buy the thermostat you want and don't worry about it.

  • I wasn't too concerned about finding a cheaper one. I was more just asking to confirm that I need not match the existing 22 amp as it is overkill for my system as i have been having a damn hard time finding a programmable line volt stat in 22amp. 15amps are more plentiful. – Zipper1365 Nov 21 '18 at 14:59
  • Oh, well if you want to fantastically fatten your choices for thermostat, add a 24V transformer and 24V A/C contactor (which are rated for motor loads, resistor loads are much easier on the contacts) and that will let you use any common 24V thermostat like a Nest. We have Q&A that address that. – Harper Nov 21 '18 at 21:06
  • Hmm. Sounds a bit beyond my present skill/comfort level, but I'm going to look into that as an upgrade option later on. Thanks – Zipper1365 Nov 22 '18 at 0:09

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