I have one of those liquid-filled electric radiator heaters in my attic office for the particularly cold days (like today), and there’s something about it that I’ve always wondered.
It has three power settings: 600W, 900W and 1500W. I assume the way this works is that there are two seperate heating elements set up to use 600 and 900W, respectively, and the 1500W setting just turns them both on.
It also has a thermostat that’s independent of the power setting.
My question is: so long as I set the thermostat, does it matter which power setting I use? I would assume that if it’s on the 1500W setting, it will still get to the same temperature, but spend less time switched on and actually heating the thing up, ultimately using approximately the same amount of energy as if I had it set to 600W and it spent more of its duty cycle switched on.
The only reason I can think to prefer one power setting over another are: A) in 600W mode, it may be possible to set the thermostat high enough that it will never actually reach that temp, so it will be on 100% of the time. and B) 1500W can be too much load for some household circuits, depending on what else is on them.
Are there any other reasons? In terms of efficiency, which is better: high power and fast heating cycles, or lower power and longer heating cycles? I figure the differences are going to be pretty marginal, but let’s nitpick.
To answer your question, no, all electric resistance heaters are equally (near 100%) efficient at converting electricity to heat. As long as under both scenarios your attic ends up at the same temperature for the same period of time, you are using exactly the same amount of electricity.
About overloading a circuit: I have a couple of space heaters that I’ve used and if I try to run it full tilt with anything else drawing much of anything, my home’s circuit breaker will trip.
They work how you described. One reason to use a lesser power is it will run longer and not turn on for 30 seconds every 2 minutes. The thermostat contacts will last longer and the fan will circulate heat around the room longer.
You are supposed to run 1500 watts max per 20 amp circuit. This is why all the heaters only have a combination of heating elements totaling 1500 watts.
I mention it to verify the OP’s hypothesis B. If you have other things on the circuit, maybe 600W is all you can do…or 900W. But if you want max output and can dedicate a circuit, you can go 1500W.
You may be more comfortable over time with the 600 or 900 watt setting than with the 1500 watt setting.
When the thermostat turns on, it begins heating the liquid to as high a temperature as the wattage will allow. The liquid remains at that temp*, as the room heats up to the thermostat’s set point. At that point, the thermost turns off, but you’ve still got a radiator full of liquid at a much higher temperature. That’ll cause the room to continue heating until the liquid cools. It might even make things uncomfortably hot for a bit. On the other hand, that excess heat might cause you to set the thermostat lower so as to avoid getting too hot, which might cause you to get too cold between thermostat cycles. The best setting for comfort depends on how close you are to the heater, how fast the room leaks heat etc. etc.
That said, the reason liquid filled heaters are so popular is that they minimize the speed of the roasting/freezing cycles inherent to any intermittent heater.
*Actually liquid temp will slowly increase as the temperature differential with the room as a whole gets smaller, but that’s a secondary effect, you’re dumping a constant number of watts per minute into the oil.
That said, the reason liquid filled heaters are so popular is that they minimize the speed of the roasting/freezing cycles inherent to any intermittent heater.
Another reason is safety.
The liquid filled heaters have an upper temperature limit safety. If a jacket or something is dropped over it it will shut off. Most also have a tip safety. If it is knocked over it will shut off.
A normal resistance element heater soes not have these safeties. I have seen a jacket begin to smoke in minutes when knocked off the back of a chair onto a heater.
In the state of Calif. it is ilegal to use anyting but a liquid filled heaters with a tip safety in the work place.
A slight aside… I got a ceramic space heater that osculates. I quickly discovered that in my medium sized bedroom while osculating it would turn itself off and say it was at the set temp (71) when it felt much cooler. I figured the osculation was somehow “bouncing” heat currents off walls and some were directed back right at the thermostat. Setting it to non-osculation and pointed roughly to the center of the room seems to work somewhat decently… But sometimes it says 71 and I’m sweating (its not just me, really, it gets HOT) and I set it down to 67 for a while. Then it gets lower and the opposite problem happens… it gets cold… happens once every few days.
I’m trying to figure out why, if the thermostat is a problem, doesn’t it stick a few degrees high or low and why osculation would seem to have some impact (though that was only my own experience, not a large sample group there). And if it is a problem of too high then too low… uh… what would cause that?
heh… Guess that’s what happens when you throw something that looks like oscillation through dictionary.com and go “oh, ok, I did spell it right in that tense” and don’t read the deff.
