General > General Technical Chat
Comparing heating power
Marco:
There's window air conditioners with heating mode too.
akis:
You are right to say that you are not getting the power you need out of small electrical radiators *all the time*, but it is a grey area, because they cannot heat up until they melt. It is like using your electric oven, it is not "on" all the time, it only heats up when it needs to, otherwise it would self destruct.
All the electric heater knows is that it is too hot and needs to switch off. It does not know how cold it is at the other end of the room.
So it is not a scam or misreporting, in my opinion. You just have to be aware how it works.
By the way it is a very similar situation with heat pumps. Their flow temperatures are low, like 45C-50C, so that even large convection radiators cannot generate enough airflow and the house remains cold. New heat pump installations now demand larger radiators to account for this and people who replace their gas boilers (typical 25kW-35kW) with air source heat pumps (typical 8kW-12kW) also have to replace radiators in the house with larger ones.
There is a heat pump manufacturer I know of who make a radiator with fan for this reason.
EPAIII:
If you are going to question the efficacy of one portable electric heater vs another, then you need to actually measure the amount of current/power they are consuming.
And comparing a device that has a thermostat against one that does not is not really fair. OK, if a heater runs 100% of the time, consuming 1380 Watts (115 V x 12 Amps which is what they are designed for in the US for safety reasons because many/most circuits are 15 A, not 20 A and they leave a bit of headroom) then it is going to produce less heat than a similar heater that has a thermostat which is set at a temperature that causes it to cycle. That's only logical.
I have said that I have a lot of experience with the oil filled, radiator style electric heaters. They usually have three heat settings and a thermostat. The ones I have used, all purchased at Walmart, can be set for full power and with the thermostat set to the maximum they will stay on 100% of the time until the room reaches a temperature that is uncomfortable. If you run them under these conditions I believe you will find that they heat a room just as fast as a electric heater that consumes the same amount of power with no heat level setting or thermostat. That is just plain physics. Neither one can magically produce any additional, extra heat, perhaps from the twilight zone. They just can't. And if you somehow "observe" a difference, you are somehow fooling yourself.
I have seen some shocking prices on some portable electric heaters. They usually are attached to models that have some "sexy" feature that is highly touted in the ads or on the box. This is called MARKETING. It has nothing to do with performance of the units. And anyone paying those prices should also look into some Florida swamp land.
Siwastaja:
--- Quote from: akis on December 20, 2023, 10:07:31 pm ---I also have a small, electrical radiator on wheels, which is 2000 watts. It is about 1/3 of the size of the large radiators, all of which are listed as 1500-2000 watts (at Dt50).
...
Would anyone know how to compare the two power ratings?
--- End quote ---
As wraper has said, it's a scam rating. It's a temporary peak power rating, just like consumer audio was sold under claims like "100W PMPO" for a 5W amplifier. But if you are heating a room, all this high peak power does is cause annoying clicking of the safety thermostat, average power is what heats your room, and it's around half of the scam rating, if even that for the cheapest crap. The rest of the power difference you are seeing is thanks to higher than 50degC dT.
It's a shame, the whole argument why oil-filled electric heaters would make sense is the supposedly lower surface temperature compared to those with a red hot glowing element exposed to air and therefore dust. But the underengineered oil-filled heaters have way too much power for way too little surface area, which is why they get >100degC hot and still cause the annoyance of the "burning dust" smell, and additionally they pump even more power rating to the specs making the safety thermostat now a frequently switching part of the design, which also increases the risk of catastrophic failure and fire because they seldom have a third thermostat in the design and the one which really should be a safety device is now stressed to tens of thousands of on-off cycles during the lifetime. By just using a resistor element rated to half the power, the thing would consume the same energy, produce the same amount of heat, cause less unnecessary acoustic noise, be more safe, but they would have to print a smaller number on the box.
This design should be simply made illegal, along the lines of: "designer must calculate the heating power of a portable radiator such that the device is physically able to dissipate the produced heat without surface temperature exceeding 80degC*, when all thermostats and thermal switches are bypassed and device is operated in conditions as explained in manual. The only purpose of safety switches is to prevent fire in case of user errors (e.g. covering of the heater) and unexpected technical failures."
*) or whatever is considered safe enough to touch
wraper:
--- Quote from: akis on December 23, 2023, 09:34:03 am ---You are right to say that you are not getting the power you need out of small electrical radiators *all the time*, but it is a grey area, because they cannot heat up until they melt. It is like using your electric oven, it is not "on" all the time, it only heats up when it needs to, otherwise it would self destruct.
All the electric heater knows is that it is too hot and needs to switch off. It does not know how cold it is at the other end of the room.
So it is not a scam or misreporting, in my opinion. You just have to be aware how it works.
--- End quote ---
It is a scam when you put additional heating element that is disabled after a few minutes regardless of room temperature. It's a deception only so they can write higher power on the box. It's separate from actual temperature control that you can regulate. Thermal switch is attached directly to the radiator and disables part of the heater. The thing is lower power part of the heater is absolutely enough to reach temperature above thermal switch activation.
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