Comparing heating power - Page 1
Forum section: electronics / general

author: akis
author_rank: Frequent Contributor
timestamp: December 20, 2023, 10:07:31 pm
content: The power of convection radiators is mentioned in Dt50 which means the power emitted by the radiator when there are 50C difference between radiator and ambient (eg radiator at 70C, ambient at 20C, Dt=50C).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).I suspect that the Dt50 power of convection radiators is not equivalent to the power of the electrical radiator.Would anyone know how to compare the two power ratings?

author: u666sa
author_rank: Frequent Contributor
timestamp: December 21, 2023, 08:11:54 pm
content: All I know, through experience, is that no modern store heater can touch my old Soviet heater at 2 killowatts, 2 bulbs, 1 killowatt each. Nothing comes close. So they must be lying somehow on their specs. Tested in cold winters.

author: MathWizard
author_rank: Super Contributor
timestamp: December 21, 2023, 10:32:53 pm
content: Do you have a way to measure temperature ? Even like how long it takes to heat up a glass of cold water in front of it, up on some block of wood or something ?

author: wraper
author_rank: Unknown
timestamp: December 21, 2023, 10:37:45 pm
content: Quote from: akis on December 20, 2023, 10:07:31 pmDo you mean an oil radiator? Most of them are scams. They theoretically have power they claim. However thermal switch will disconnect part of heating elements when it gets hot, so it will consume rated power only for a few minutes. So your 2000W heater will suddenly become 650W.

author: themadhippy
author_rank: Super Contributor
timestamp: December 21, 2023, 10:57:24 pm
content: QuoteHow much of that is down to seeing a red glow so the brain thinks its hot? I remember elderly relatives who would turn on just the red lamp in there fire to take the chill out the room

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 22, 2023, 02:01:25 am
content: Quote from: wraper on December 21, 2023, 10:37:45 pmSeen that.The bottom line anyway is that there's no such thing as better efficiency for a pure electrical heater (not a heat pump) that only generates it by Joule effect.What comes in will get out. Apart from maybe some minor electronics, if there is any, which will *not completely* transform all energy into heat (maybe a few mW), the rest will. So you effectively get almost 100% efficiency.The only difference is in how a given heater radiates/convects heat, and a heater with more inertia (such as those oil ones) will tend to heat up air more slowly but a bit more homogeneously in a room, at least until it reaches equilibrium. Which often gives a bit more subjective comfort. But the average temperature inside the room will be the exact same for the same amount of energy.And so yes, some of these heaters that claim "better efficiency" just trick people with a bounded duty cycle - effectively drawing less power on average - which will just, uh, heat up a room less by the same amount. The inertia may just trick people a little bit, giving some improved comfort (as temperature decreases more slowly when off), but that doesn't change the temperature in the room whatsoever. Less power = lower temperature.

author: EPAIII
author_rank: Super Contributor
timestamp: December 22, 2023, 03:24:16 am
content: All portable electric heaters are simple devices that convert electric power to HEAT. Since they do not emit light or RF or other forms of energy, the electric power they consume is converted 100% into heat. Not 99% and not 101%. But EXACTLY 100%. PERIOD.And that electric power is exactly equal to Voltage multiplied by current: P = V * I. SO, if two portable electric heaters both consume 15 Amps at 115 VAC, then both of them produce EXACTLY 1725 Watts of HEAT. None of them, no matter what the design may be, can produce any more or any less heat if they consume that amount of electric power.Now, there may be some other advantages of oil filled vs radiant vs whatever design, but a different amount of heat is not among them. I have oil filled electric radiators in my shop and bedroom. I like them for safety reasons.The only way of producing more heat in an electric heater is with a HEAT PUMP. A heat pump will move heat energy from the outside environment into the building. A heat pump can do this even when the temperature is lower outside than inside. This is the same as an air conditioning unit which moves heat from the cooler interior of a building to the hotter exterior: they operate in reverse of each other. But heat pumps are not portable, they are installed in the building with pipes/tubes carrying gas and liquids back and forth between inside and outside.Once again, all portable electric heaters are exactly 100% efficient. None are even a millionth of a percentage point higher or lower than that. This is basic physics and basic electricity.

author: themadhippy
author_rank: Super Contributor
timestamp: December 22, 2023, 04:00:40 am
content: Quotewhat about infra red,isnt that classed as light?

author: EPAIII
author_rank: Super Contributor
timestamp: December 22, 2023, 04:25:05 am
content: Sorry, any "minor electronics" will also turn the electricity it uses 100% into heat. The ONLY ways energy can escape the room is as light going out a window or RF energy that goes through the walls. But space heaters generate no RF and only a very small amount of light (LED indicator) and 99.99% or more of that light will strike the people, animals, furnishings, floor, ceiling, and walls and be absorbed and converted to HEAT.If any energy escapes the room, it won't be milliWatts, not even a reasonable fraction of one. More like microWatts or nanoWatts.Once again, if it consumes X Watts of electricity, it will produce X Watts of heat IN THE STRUCTURE. No more and no less.I have used the oil filled radiators for over 20 years. They work with a thermostat, just like central heating systems. Yes, they can switch off if the temperature rises above the set point, but so what. In cold climates (Iowa, USA where the mercury can go below the readings on the thermometer) I have seen them just run 100% of the time, never catching up with the cold. It just depends on where YOU set the control. The oil filled radiators actually work very well and they almost never break.Quote from: SiliconWizard on December 22, 2023, 02:01:25 am

author: EPAIII
author_rank: Super Contributor
timestamp: December 22, 2023, 04:41:32 am
content: OK, I had not thought of that. So, perhaps any electric heater that produces a glow or even invisible IR radiation can have some of it lost out of the windows and to a lesser extent, the walls.That makes the ones that do not glow or get hot enough to make a lot of IR look like the winners. Oil filled radiators may come out on top.And if you want to keep that IR heat, just close the blinds or curtains.Hey, I understand the allure of a glowing fire. When I was growing up our house had a gas fireplace, complete with a chimney. My dad would lie in front of it, on the floor and enjoy the radiant heat while napping. I did the same, on occasion. It was nice. Probably something in the human genome after centuries of homes with hearths. But modern science says the central heating system is better engineered than those fireplaces were. And I think the portable, space heaters that do not glow are also probably a bit more efficient. But, as I said, we can enjoy something that is not the best from an engineering point of view. A roller coaster is hardly the best roadway, but we love them.Quote from: themadhippy on December 22, 2023, 04:00:40 am

author: akis
author_rank: Frequent Contributor
timestamp: December 22, 2023, 06:26:23 am
content: Hi guys, I have not explained well what information I was after.There is no doubt that electric devices (eg hairdryer, electric heater, kettle etc) are exactly what's on the label and really generate 2000W of heat if the label says so. I have also verified with power meter.From past experience, and recent tests into a 20m2 room, with 5 thermometers around the room and fan assisted heating, I can say that 2000W is not enough to warm this room from say 13C up to 20C in reasonable time (2 hours). Actually it never reaches 20C (outside temps anything from 0C to 12C) - I switch it off at about 17C-18C.Central heating, water filled radiators, report their power (in watts) based on the strict condition that [ radiator temp - room temp = 50C, known as "Dt50" ]. To explain this metric, when your radiator is at 70C (average) and your room is at 20C, the difference being 50C, at that precise point the radiator is said to emit 2000W of heat.Intuitively I know that those radiators produce 2-3 times the heat of the hair dryer or the electric heater, but they are all rated at the same wattage, 2000W.It follows that the Dt50 power rating for water filled, central heating radiators, cannot be readily compared to our tried and tested electrical power ratings.Is there a rule of thumb equivalence or conversion, between Dt50 and electrical power ratings?

author: wraper
author_rank: Unknown
timestamp: December 22, 2023, 08:21:58 am
content: Quote from: akis on December 22, 2023, 06:26:23 amFar from that. As I said about oil radiators, they technically don't lie about power rating but are an utter scam because they consume rated power only while heating up with some rare exceptions, which are, surprise, much larger than the rest. Even My $170 1500W oil radiator does this, albeit to lower extent than cheap ones, becoming about 900W IIRC. It has 3 power level settings, highest one being utterly useless.

author: akis
author_rank: Frequent Contributor
timestamp: December 22, 2023, 08:48:37 am
content: Quote from: wraper on December 22, 2023, 08:21:58 amThe electrical heater does not have enough surface area to generate adequate air flow by convection only. It gets really hot and switches off even though the room is cold.I have put an upright fan behind my electrical heater, like a fan assisted heat sink, and the glow light never goes off, so I know it is consuming full power.I have placed 5 thermometers in the room and they record different temperatures, about 2C-3C difference from side to side, and maybe up to 5C difference from floor to ceiling. This is with fan active in the room. It would be much worse with fan off.

author: wraper
author_rank: Unknown
timestamp: December 22, 2023, 08:56:32 am
content: Quote from: akis on December 22, 2023, 08:48:37 amSo you just confirmed its specs are an utter deception, external fan is not part of the radiator, and not how it's intended to be used. Original question implies why some radiators with same power rating are larger than others? Yes there are radiators with true power rating and no deceptive practices, Delonghi Dragon for example.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 22, 2023, 01:11:53 pm
content: Quote from: EPAIII on December 22, 2023, 03:24:16 amPortable heat pumps exist.https://www.midea.com/us/air-conditioners/portable-air-conditioners/midea-duo-12-000-btu-sacc-smart-inverter-portable-air-conditioner

author: Marco
author_rank: Super Contributor
timestamp: December 22, 2023, 01:27:03 pm
content: There's window air conditioners with heating mode too.

author: akis
author_rank: Frequent Contributor
timestamp: December 23, 2023, 09:34:03 am
content: 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.

author: EPAIII
author_rank: Super Contributor
timestamp: December 23, 2023, 10:52:38 am
content: 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 23, 2023, 12:08:58 pm
content: Quote from: akis on December 20, 2023, 10:07:31 pmAs 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, andadditionallythey pumpeven morepower 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

author: wraper
author_rank: Unknown
timestamp: December 23, 2023, 12:15:23 pm
content: Quote from: akis on December 23, 2023, 09:34:03 amIt 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 25, 2023, 12:31:23 am
content: Too bad there's no standardized way to test how much "usable" heat a heater would provide in a typical real world situation. I would expect radiators to do especially poor with high ceilings but work OK with lower ceilings.

author: wraper
author_rank: Unknown
timestamp: December 25, 2023, 01:02:08 am
content: Quote from: NiHaoMike on December 25, 2023, 12:31:23 amAll of the heat will go inside of the room anyway. But as halogen heater lamp mainly heats through radiation, in close proximity you'll feel warm even if air is actually cold because it heats you directly. All electric heaters are 100% efficient. With larger distance it's not like thermal radiation will be lost, just spread over larger area.

author: Dacian
author_rank: Contributor
timestamp: December 25, 2023, 05:47:18 am
content: Quote from: akis on December 20, 2023, 10:07:31 pmThey are fully equivalent.If you have any type of electrical heater that uses 2000W it will be exact equivalent of that water filled convection radiators.Of course if either the electric heater or water radiator has a thermostat that stops the output for say 50% of the time then net energy delivered to room will be that 50%.I fully heat my house with solar PV so I have embedded copper wires in to the concrete floor that works as in floor heating elements and the floor works as a very large thermal storage about 93kWhI also have a solar panel installed on a wall and that is also a heater basically made of 60 diodes in series and is directly connected to PV panels installed outside no electronics and it naturally works at the max power point.I will first concentrate on thermal insulation if you want to improve the comfort of your room. And maybe consider a heat pump if your outside temperature is mild in winter. I'm in Saskatchewan Canada and normally (except this winter) is way to clod here for a air to air heat-pump.

author: BrokenYugo
author_rank: Super Contributor
timestamp: December 25, 2023, 06:05:21 pm
content: Quote from: akis on December 22, 2023, 06:26:23 amThis is the cause of your confusion, DT50 does not specify output, it specifies the test procedure to measure the output of a hot water radiator, which could be anything depending on the size and design.This paragraph I copied off some UK radiator store's site explains it well.QuoteThe idea being that one could cheat and overinflate the stated output by placing the radiator in a very cold room or using hotter feed water, so the conditions are fixed for the sake of fair comparison. The physics of a resistive electric heater are different, the only variable there is watts from the wall, as all power in is converted to heat out. The only way you can really cheat with an electric heater is to cram more heating element in than the heater can continuously dissipate in a typical use case, but a cheap power meter will show that easily.As others have mentioned, any perceived differences in equal output heaters are down to how the heat is transferred. Radiant usually feels best, the larger the better, like some of the best heat you can get is a machine shop full of big multi ton iron machines, those are always nice in winter, I imagine in floor radiant gives a similar effect.

author: RJSV
author_rank: Super Contributor
timestamp: December 25, 2023, 11:06:55 pm
content: My guess is that THERMAL radiation, and even the patterns of I.R. emission matter, especially when it's a complex animal (us humans). Consider the case where virtually all of I.R. emissions go straight up to roof, while the poor shivering human sits, figgiting with controls, to get more heat.My guess is that an oil filled vessel radiates in various bands, including I.R. and surfaces are significant to the emissions results, for various optical bands and intensitys. A reflective chrome coating can have a lot of effect, vs an anodized black coating. (I couldn't say which is best, but surfaces matter, for electromagnetic emissions.